Illustration of leukocyte development

Illustration of antibody structure
Illustration of antibody response

  • To convert cells/μl to cells/liter, multiply by 1000000. So 2500 cells/μl = 2.5 X 109 cells/L
  • Normal values may vary by lab
Neutrophil levels in adults
Range Absolute neutrophil count
High > 7500 May occur from an overall increase in neutrophils or a shift from bone marrow to the circulation
Normal 2500 - 6000 Neutrophils typically account for 40 - 60% of total WBCs
Mild neutropenia 1000 - 1500 Not associated with an increased risk of infection
Moderate neutropenia 500 - 999 Slight increased risk of infection in some patients
Severe neutropenia < 500 Increased risk of infection in most patients
Band neutrophils
Normal 0 - 500 Neutrophil bands typically account for 0 - 5% of total WBCs
Left shift > 500 Typically a sign of bacterial infection

  • Reference [8,9,10,11,12,13]
Causes of neutropenia
Congenital neutropenia
Benign ethnic neutropenia (BEN)
  • BEN is a condition seen in people of certain ethnic backgrounds, particularly Mediterranean, Middle Eastern, and African. ANC counts < 1500 occur in 4.5% of healthy blacks in the U.S. BEN is believed to be related to polymorphisms in the Duffy antigen receptor complex (DARC) gene that affect neutrophil release from the bone marrow. Therefore, the neutropenia in BEN is thought to be related to a decrease in circulating neutrophils as opposed to an overall deficit. ANCs in BEN are typically between 1000 and 1500, and affected individuals are not at increased risk of infection. Healthy individuals from susceptible populations with persistent ANCs (> 3 months) of 1000 - 1500 can be assumed to have BEN and do not require further workup. Patients with concerning symptoms (e.g. history of recurrent fever, frequent infections, severe oral ulcers, lymphadenopathy, splenomegaly) should undergo further evaluation. [8,9,10]
Benign familial neutropenia
  • Benign familial neutropenia is similar to benign ethnic neutropenia in that it presents as a chronic, mild neutropenia in otherwise healthy individuals, but unlike BEN, it is not associated with any particular ethnic group. [8]
Cyclic neutropenia
  • Cyclic neutropenia is a rare inherited disorder that is marked by episodes of severe neutropenia that recur every 2 - 5 weeks. The severity and length of neutropenia varies among individuals, but in most cases, it is mild. Patients with severe disease may experience infections and oral ulcers during episodes, and neutrophil counts can go to zero for 2 - 5 days. The genetic defects seen in cyclic neutropenia are related to the ones that are found in severe congenital neutropenia. Patients with severe disease may be treated with granulocyte-colony stimulating factor (G-CSF) and/or corticosteroids. [8,11]
Severe congenital neutropenia (SCN)
  • SCN is a group of rare inherited disorders that affect neutrophil development in the bone marrow. Affected individuals have severe neutropenia soon after birth, and they develop recurrent infections during the first year of life. SCN used to be uniformly fatal, but now patients can be treated with granulocyte-colony stimulating factor (G-CSF); bone marrow transplant is the only curative treatment. Patients with SCD have a 10 - 30% lifetime risk of acute myeloid leukemia. [8]
Acquired causes
  • Infections can cause neutropenia both during and after the infectious process. Post-infectious neutropenia is more common, and it typically occurs in children after viral infections. Any virus can cause post-infectious neutropenia, but the most common culprits are cytomegalovirus, Epstein-Barr virus, HIV, influenza, varicella, measles, rubella, and parvovirus B19. Bacterial-induced neutropenia is less common, but can occur with rickettsial diseases, mycobacterium, brucella, and typhoid. Neutropenia during sepsis is a dire sign. [8,9]
Drug-induced neutropenia
  • A number of medications have been associated with neutropenia. Some drugs are obvious and frequent causes, because their mechanisms directly affect hematopoiesis (e.g. chemotherapy, biologicals). Other drugs have been associated with neutropenia through case reports and postmarketing surveillance. Causality with these medications is not as clear, and the mechanism is not completely understood but may involve drug-induced autoimmune antibodies and/or direct inhibition of hematopoiesis. The table below lists drugs that have been associated with neutropenia and divides them by drug class and strength of association. [8,9,12]

Drugs that are known to cause neutropenia
  • Biologicals
    • Anakinra (Kineret®)
    • Brodalumab (Siliq®)
    • Ixekizumab (Taltz®)
    • Rituximab (Rituxan®)
    • Sarilumab (Kevzara®)
    • Tocilizumab (Actemra®)
  • Chemotherapeutic agents
    • Alkylating agents (e.g. cyclophosphamide, chlorambucil, busulfan, cisplatin, carboplatin)
    • Antimetabolites (e.g. fluorouracil, cytarabine, methotrexate, gemcitabine)
    • Anti-tumor antibiotics (e.g. doxorubicin, daunorubicin, mitomycin-C, bleomycin)
    • Topoisomerase inhibitors (e.g. topotecan, etoposide, mitoxantrone)
    • Mitotic inhibitors (e.g. docetaxel, paclitaxel, vincristine, vinblastine)
  • Immunosuppressants
    • Azathioprine (Imuran®)
    • Baricitinib (Olumiant®)
    • Mercaptopurine (Purixan®)
    • Methotrexate (Trexall®)
    • Mycophenolate (Cellcept®)
    • Sulfasalazine (Azulfidine®)
    • Tacrolimus (Prograf®)
    • Teriflunomide (Aubagio®)
    • Tofacitinib (Xeljanz®)
    • Upadacitinib (Rinvoq®)
  • Other
    • Clozapine (Clozaril®)
    • Deferiprone
    • Methimazole
    • Pegylated interferon (Pegintron®, Pegasys®)
    • Ticlopidine (Ticlid®)

Drugs that have been associated with neutropenia
  • Antibiotics
    • Cephalosporins
    • Chloramphenicol
    • Chloroquine
    • Ciprofloxacin
    • Clindamycin
    • Dapsone
    • Linezolid (Zyvox®)
    • Macrolides
    • Metronidazole (Flagyl®)
    • Penicillins
    • Quinine
    • Sulfonamides
    • Vancomycin
  • Antiepileptics
    • Carbamazepine (Tegretol®)
    • Ethosuximide
    • Levetiracetam (Keppra®)
    • Phenytoin (Dilantin®)
    • Valproic acid (Depakote®)
  • Antifungals
    • Amphotericin
    • Flucytosine
  • Antimalarials
    • Chloroquine
    • Quinine
  • Anti-inflammatory
    • Ibuprofen
    • Diclofenac
    • Gold salts
    • Penicillamine
  • Cardiovascular drugs
    • ACE inhibitors
    • Digoxin
    • Flecainide
    • Procainamide
    • Propranolol
  • Diuretics
    • Acetazolamide
    • Furosemide
    • Spironolactone
    • Thiazides
    • Torsemide
  • Psychotropic agents
    • Clorpromazine (Clozaril®)
    • Olanzapine (Zyprexa®)
    • Quetiapine (Seroquel®)
    • Tricyclic antidepressants
    • Venlafaxine (Effexor®)
  • Other
    • Propylthiouracil
    • Valganciclovir
Autoimmune neutropenia
  • Autoimmune neutropenia occurs when auto-antibodies form against neutrophil antigens, typically cell membrane glycoproteins. These antibodies can cause neutrophil destruction that leads to neutropenia. Autoimmune neutropenia can occur in isolation or it can be a part of other autoimmune diseases (e.g. rheumatoid arthritis, lupus). Different types of autoimmune neutropenia are reviewed below.

  • Neonatal alloimmune neutropenia - neonatal alloimmune neutropenia occurs from anti-neutrophil IgG antibodies that are passed from mother to infant. Maternal anti-neutrophil antibodies develop from sensitization to paternal antigens, and they are seen in 1 - 3% of live births. Most newborns born with anti-neutrophil antibodies do not develop neutropenia, but in some cases, significant neutropenia that leads to fevers, urinary tract infections, cellulitis, pneumonia, and sepsis can occur. The disorder typically resolves around 7 weeks of age when maternal antibodies decay. Severe or prolonged cases may require G-CSF.

  • Primary autoimmune neutropenia - primary autoimmune neutropenia, also referred to as "chronic autoimmune neutropenia of infancy and early childhood," is a neutropenic syndrome that occurs in infants and children. Most affected individuals have auto-antibodies to neutrophil surface antigens, but they are not always present. The disease is typically mild and self-limited with a mean duration of 17 months. In severe cases, prophylactic antibiotics and G-CSF may be required.

  • Chronic idiopathic neutropenia - neutropenia that is acquired in adulthood and has no identifiable cause is referred to as "chronic idiopathic neutropenia." It is also sometimes called "autoimmune neutropenia," and the two terms are used interchangeably in the medical literature. Chronic idiopathic neutropenia is a diagnosis of exclusion and can only be made after other causes of neutropenia have been excluded. Women are affected more than men (5:1), and the neutropenia can range from mild to severe. Anti-neutrophil antibodies can be detected in some individuals, but not all. The clinical course is typically benign, even in patients with severe neutropenia. Severe cases may require G-CSF.

  • Secondary autoimmune neutropenia (SAN) - SAN occurs in patients who have other autoimmune disorders. Conditions in which SAN is known to develop include rheumatoid arthritis, systemic lupus erythematosus (up to 50% of patients), granulomatosis with polyangiitis, and chronic hepatitis. Most cases of SAN are mild and do not require any treatment. Patients with rheumatoid arthritis sometimes get a condition called Felty syndrome that is marked by neutropenia and splenomegaly. Felty syndrome is usually only seen in severe, deforming disease, and it has become much less common with the advent of effective disease-modifying therapies. [8,9,13]
Hematologic disorders
  • Any condition that affects hematopoiesis can cause neutropenia. These conditions usually fall under one of the following: (1) myelodysplastic syndromes, (2) hematologic malignancies (e.g. leukemia, lymphoma), (3) rare congenital disorders that directly or indirectly alter hematopoiesis. A bone marrow biopsy is usually required to diagnose these conditions. Most of the time, malignancies and myelodysplastic syndromes present with other hematologic abnormalities. One exception is large granular lymphocytic (LGL) leukemia which is a chronic leukemia that can present as isolated neutropenia. [8,9,13]
Nutritional disorders
  • Some nutritional disorders can cause neutropenia. Caloric malnutrition (e.g. anorexia) can cause neutropenia as can vitamin B12, folate, and copper deficiencies. These deficiencies almost always present with other hematologic abnormalities (e.g. megaloblastic anemia with vitamin B12 and folate deficiency) and are rarely a cause of isolated neutropenia. Copper deficiency is uncommon, but may be seen in patients who have undergone gastric bypass surgery. [8,9,13]

  • Reference [8,9]
Steps to evaluating neutropenia
Step 1 - Assess the degree of neutropenia
  • ANC < 500 cells/μl - patients with an ANC < 500 are at increased risk of infection. Febrile patients (temp > 100.4°) should be admitted to the hospital immediately and started on IV antibiotics that cover Pseudomonas aeruginosa and other gram-negative bacteria. Afebrile patients who are otherwise healthy may need to be admitted depending on the situation.
  • ANC 500 - 1500 cells/μl - patients with new-onset neutropenia or neutropenia of unknown duration who have signs of an acute infection (e.g. fever) should be admitted to the hospital. Otherwise healthy patients with neutropenia discovered on routine lab work can be evaluated as outpatients.
Step 2 - Order labs and determine if the neutropenia is chronic or new onset
  • Order the following labs
    • Serial CBCs - if old CBCs are not available or neutropenia is a new finding, repeat CBCs over the course of days to weeks can establish a trend in the ANC. If cyclic neutropenia is suspected (e.g. recurrent fevers/infections/mouth ulcers, family history, history of variable neutrophil counts) twice weekly CBCs for 4 - 6 weeks can establish a pattern.
    • Peripheral smear or pathologist's review
    • HIV test
    • CMP
  • Chronic stable neutropenia (> 3 months)
    • Patients with chronic stable neutropenia who are healthy and have no concerning symptoms (e.g. history of recurrent fever, frequent infections, severe oral ulcers, lymphadenopathy, splenomegaly) likely have some form of benign neutropenia (e.g. benign ethnic neutropenia, benign familial neutropenia) and no further workup is necessary
    • Recurrent infections seen in chronic neutropenia include pneumonia, sinusitis, dental caries, and skin/soft tissue infections; these infections are uncommon unless the ANC is < 500 cell/μl
  • New-onset neutropenia
    • Review medications for drugs associated with neutropenia (see drug-induced neutropenia)
    • Ask patient about recent infections
Step 3 - Based on findings, consider the following
  • Possible drug-related neutropenia
    • If patient is healthy, stop the offending drug if possible. Monitor ANC and see if it returns to normal.
  • Possible infection-related neutropenia
    • If patient is healthy, monitor ANC and see if returns to normal after infection resolves
  • Patient has findings consistent with vitamin B12/folate deficiency
    • Findings consistent with vitamin B12/folate deficiency include macrocytosis, hypersegmented neutrophils, and pancytopenia
    • Check vitamin B12 and folic acid levels. If levels are normal, proceed to bone marrow biopsy.
  • Patient has no other hematologic abnormalities
    • Proceed to bone marrow biopsy
  • Other labs to consider depending on the situation
    • Copper level - if patients has history of gastric bypass
    • ANA, rheumatoid factor, ESR, C-reactive protein - to screen for secondary autoimmune neutropenia
    • Serum immunoglobulin levels - to screen for immunodeficiencies
    • Antineutrophil antibodies - antineutrophil antibody tests are available at some labs. In adults, the test is not very useful since a significant portion of the normal population has these antibodies, and there is no evidence that antineutrophil antibody-positive patients respond to immunosuppressive therapy. Antineutrophil antibody assays also have a high false-positive rate for the presence of antibodies due to certain characteristics of neutrophils.

  • Reference [14,15,16,17]
Causes of neutrophilia
  • Infections are the most common causes of neutrophilia. During an infection, total body neutrophils may increase up to 6-fold. In the very early stages of an infection, circulating neutrophil counts may decrease briefly as neutrophils shift into tissues. This is quickly offset by increased marrow production and migration of neutrophils from the marrow into the circulation. High marrow output will also cause a "left shift" in circulating neutrophils which means more immature neutrophils (e.g. bands) can be seen in the blood. Many types of infections can cause neutrophilia, but bacterial infections are the most common cause.
    • Organisms that can cause neutrophilia include the following:
      • Bacteria (most common)
      • Fungal infections (e.g. Coccidioides immitis, Candida albicans)
      • Spirochetes
      • Viruses (e.g. rabies, poliomyelitis, herpes zoster, smallpox, varicella)
      • Rickettsia
      • Parasites
High cortisol/epinephrine states
  • Conditions that increase the release of cortisol can lead to neutrophilia. Cortisol increases circulating neutrophils through the following mechanisms: (1) stimulation of neutrophil maturation in the bone marrow, (2) promotion of neutrophil release into the circulation, (3) inhibition of neutrophil migration into inflamed tissues, (4) prevention of neutrophil apoptosis. Epinephrine causes a transient shift of neutrophils from tissues into the circulation.
    • High cortisol/epinephrine states associated with neutrophilia include the following:
    • Asthma exacerbation
    • Bowel obstruction
    • Burns
    • Cardiopulmonary bypass surgery
    • Corticosteroid therapy
    • Cushing's disease
    • Epinephrine injections
    • Gout flare
    • Hypersensitivity reactions
    • Pain
    • Postoperative state (12 - 36 hours)
    • Pregnancy labor
    • Myocardial infarction
    • Seizures
    • Strenuous exercise
    • Stress
Chronic inflammatory states
  • Chronic hepatitis
  • Familial Mediterranean fever (FMF) - FMF, also called recurrent polyserositis, is a hereditary disorder that causes recurrent episodes of peritonitis, pleuritis, and arthritis that are usually accompanied with fever and neutrophilia. Episodes last 12 - 72 hours, and they typically begin in childhood. The length of time between episodes can vary from days to years. The condition mostly affects people of Mediterranean descent including Arabs, Armenians, Turks, Greeks, Italians, Persians, North African Jews, and Ashkenazi Jews. FMF is caused by mutations in the MEFV gene that codes for a protein in neutrophils called pyrin. The exact function of pyrin is unknown, but it is believed to play a role in regulating inflammation. The most concerning sequelae of FMF is the development of amyloidosis which can lead to renal failure; serum amyloid increases during inflammatory attacks, and over time, can build up and cause organ damage. FMF is a clinical diagnosis, and it can be confirmed with genetic testing. The main treatment is colchicine which is highly effective at preventing both attacks and amyloidosis.
  • Granulomatous diseases (e.g. sarcoidosis)
  • Inflammatory bowel disease
  • Rheumatic fever
  • Rheumatoid arthritis
  • Vasculitis
Hematologic disorders
  • Chronic idiopathic neutropenia
  • Chronic myelocytic leukemia (CML)
  • Chronic neutrophilic leukemia (CNL)
  • Hemolytic anemia
  • Immune thrombocytopenia
  • Leukocyte adhesion deficiency
  • Megaloblastic anemia
  • Myelofibrosis
  • Polycythemia vera
  • Beta agonists (e.g. albuterol, theophylline)
  • Colony-stimulating factors (e.g. filgrastim)
  • Corticosteroids
  • Epinephrine
  • Lithium
  • Tetracycline
Other causes
  • Diabetic ketoacidosis
  • Down syndrome
  • Malignancies (e.g. lung, stomach, breast, kidney)
  • Poisoning (e.g. lead, mercury, etc.)
  • Preeclampsia
  • Pregnancy
  • Smoking - can cause a mild chronic neutrophilia
  • Splenectomy
  • Uremia

  • To convert cells/μl to cells/liter, multiply by 1000000. So 2500 cells/μl = 2.5 X 109 cells/L
  • Normal values may vary by lab
  • References [16,17,24]
Lymphocyte levels in adults
Range Absolute lymphocyte count
Lymphocytosis > 4000
Normal 1000 - 4000
(20 - 40% of WBCs)
Mild to moderate lymphopenia 500 - 1000
Severe lymphopenia < 500
  • Under normal conditions, circulating lymphocytes include the following:
    • T lymphocytes: 60 - 80%
    • B lymphocytes: 5 - 20%
    • Natural killer lymphocytes: 5 - 20%
  • Lymphocyte type can be determined with flow cytometry but not on a CBC or peripheral smear

  • References [22,23,24]
Causes of lymphopenia
Advanced age
  • As people age, their lymphocytes counts tend to decrease. Healthy elderly patients without any concerning findings that have an absolute lymphocyte count > 500 cells/μl and a normal peripheral smear do not require any further workup.
Primary immune disorders
  • Primary immune disorders are genetic disorders that affect the immune system. Lymphopenia is often a feature of these rare disorders that are marked by recurrent, severe childhood infections with uncommon pathogens. Examples of primary immune disorders include the following:
  • Severe combined immunodeficiency (SCID) - SCID is a group of inherited disorders that affect T and B cell function and/or development. Affected individuals have recurrent, severe infections during the first year of life. Most cases of SCID are X-linked inherited disorders of the IL2RG gene which codes for a protein that is part of interleukin receptors. WIthout working receptors, interleukin signalling is lost and lymphocytes do not develop correctly. Another form of SCID is caused by defects in the gene that codes for adenosine deaminase (ADA), an enzyme necessary for lymphocyte development. SCID can be treated with stem cell transplant, and in the case of ADA deficiency, ADA replacement therapy. A study published in 2021 found that autologous stem cell gene therapy with a virus carrying the ADA gene was curative in most patients with ADA-deficiency SCID. [PMID 33974366]
  • Common variable immunodeficiency (CVID) - CVID is a poorly understood condition that causes a lack of plasma cells that can produce antibodies, low levels of immunoglobulins, and frequent bacterial infections. CVID may become evident at any time from birth through the fourth decade of life. The main treatment of CVID is immunoglobulin replacement with IVIG therapy.
  • Wiskott-Aldrich syndrome - Wiskott-Aldrich syndrome is an X-linked recessive disorder that affects B and T cell signaling. The syndrome is marked by the triad of microthrombocytopenia, eczema, and recurrent infections. Treatment includes IVIG and antibiotics. Stem cell transplantation can be curative.
  • Infections are a common cause of lymphopenia. Bacterial infections typically cause a neutrophilia that coincides with lymphopenia. Fungal infections can also cause a similar WBC shift. While viral infections are a common cause of lymphocytosis, they can also present with lymphopenia. Viruses that are known to cause lymphopenia include influenza, hepatitis, and HIV. Mycobacterium and parasites have also been associated with lymphopenia.
  • A number of medications can cause lymphopenia. Some drugs suppress lymphocytes through their primary mechanism (e.g. immunosuppressants, chemotherapy) while other drugs affect lymphocytes indirectly through unknown mechanisms. Examples of drugs that may cause lymphopenia are listed below.
  • Biologics
    • Belimumab (Benlysta®)
    • Rituximab (Rituxan®)
    • Ofatumumab (Kesimpta®)
  • Chemotherapeutic agents
    • Alkylating agents (e.g. cyclophosphamide, chlorambucil, busulfan, cisplatin, carboplatin)
    • Antimetabolites (e.g. fluorouracil, cytarabine, methotrexate, gemcitabine)
    • Anti-tumor antibiotics (e.g. doxorubicin, daunorubicin, mitomycin-C, bleomycin)
    • Topoisomerase inhibitors (e.g. topotecan, etoposide, mitoxantrone)
    • Mitotic inhibitors (e.g. docetaxel, paclitaxel, vincristine, vinblastine)
  • Immunosuppressants
    • Azathioprine
    • Baricitinib (Olumiant®)
    • Cladribine (Mavenclad®)
    • Corticosteroids
    • Dimethyl fumarate (Tecfidera®, Vumerity®)
    • Fingolimod (Gilenya®)
    • Mercaptopurine (6-MP)
    • Methotrexate
    • Mycophenolate (Cellcept®)
    • Tacrolimus (Prograf®)
    • Tofacitinib (Xeljanz®)
    • Upadacitinib (Rinvoq®)
Autoimmune diseases
  • A number of autoimmune disorders have been associated with lymphopenia. In many of these conditions, treatment often involves medications that suppress lymphocytes, so the cause of lymphopenia may be a combination of the disease process and medication effects.
  • Autoimmune conditions associated with lymphopenia include:
    • Crohn's disease
    • Myasthenia gravis
    • Rheumatoid arthritis
    • Sjogren's syndrome - severe lymphopenia is seen in up to 5% of patients
    • Systemic lupus erythematosus - lymphopenia < 1500 cells/μl is part of the lupus classification criteria
    • Type 1 diabetes
    • Vasculitis
  • Alcohol abuse
  • Heart failure
  • Malignancies - hematologic (e.g. lymphomas) and solid tumor
  • Malnutrition (particularly protein deficiency)
  • Radiotherapy
  • Renal failure
  • Silicosis
  • Surgery

  • References [24,25]
Steps in evaluating lymphopenia
Step 1 - order HIV, peripheral smear, and assess the following:
  • Infections (viral, bacterial, other) within last 6 months
  • Medications associated with lymphopenia
  • History of infections that suggest underlying immunodeficiency (e.g. PCP pneumonia, severe warts, recurrent infections)
  • Symptoms or findings consistent with a systemic disease (e.g. autoimmune disorders, renal failure, heart failure, malignancy)
  • Lymphoma symptoms (weight loss, fever, night sweats)
  • Alcohol abuse
  • Abnormal physical exam findings including lymphadenopathy, splenomegaly, and rashes

  • Absolute lymphocyte count > 500 cells/μl, no concerning findings, and elderly (> 65 years)
    • No further workup recommended

  • Absolute lymphocyte count < 1000 cells/μl and < 65 years or < 500 cells/μl and > 65 years
    • Proceed to Step 2
Step 2 - further testing
  • Patients with concerning history or findings
    • Refer to hematology for evaluation

  • Patients with no concerning history or findings
    • Check CMP to assess kidney and liver function
    • Repeat CBC and peripheral smear in 6 weeks. If there is no change, repeat in 6 months. If lymphopenia is stable over 6 months and there are no other findings or symptoms, a serious condition is unlikely.

  • Other tests to consider
    • ANA and rheumatoid factor is there are signs of autoimmune disease
    • Serum immunoglobulins if there is concern for immunodeficiency

  • Reference [21,
Causes of lymphocytosis
Viral Infections
  • Viral infections are the most common cause of lymphocytosis. Bacterial infections typically cause neutrophilia, and with a few exceptions, are an uncommon cause of lymphocytosis.
  • Epstein-Barr virus (EBV) - Epstein-Barr virus infection is a common cause of lymphocytosis. The peak incidence of infection occurs between 15 - 24 years of age, and up to 95% of adults are seropositive for EBV antibodies. EBV is spread by salivary and sexual contact, and it has an incubation period of 30 - 50 days. Symptoms of EBV infection typically persist for 1 - 4 weeks and include fever, lymphadenopathy, pharyngitis, splenomegaly, and lymphocytosis. This constellation of symptoms is referred to as mononucleosis, and while EBV is the most common cause, other infections including cytomegalovirus, HIV, adenovirus, and Toxoplasma gondii can have a similar presentation. Several blood tests are available to detect EBV infection (see EBV testing below).
  • Cytomegalovirus - cytomegalovirus can cause a mononucleosis syndrome similar to EBV
  • HIV - acute HIV infection can cause a mononucleosis-like syndrome. Chronic HIV causes lymphopenia.
  • Other viruses that can cause lymphocytosis
    • Acute infectious lymphocytosis
    • Adenovirus
    • Hepatitis
    • Herpes simplex
    • Herpes zoster
    • Human T Lymphocytic virus type 1 (HTLV-1)
    • Influenza
    • Mumps
    • Respiratory syncytial virus
    • Roseola
    • Rubeola
    • Rubella
    • Varicella
Bacterial infections
  • Outside of a few exceptions, bacterial infections are an uncommon cause of lymphocytosis
  • Bartonella henselae - bartonella henselae is the bacteria that causes cat scratch disease. An atypical lymphocytosis may be seen.
  • Bordetella pertussis - pertussis causes a significant lymphocytosis, particularly in children
  • Brucella organisms (brucellosis) - brucella organisms are passed to humans from animals (e.g. sheep, pigs, cattle, dogs). Brucellosis may cause lymphocytosis, and it is also known to cause neutropenia.
  • Syphilis
Protozoan infections
  • Babesia (babesiosis) - babesiosis is a tick-borne illness that like malaria, infects red blood cells. It is endemic to the northeastern U.S.
  • Plasmodium falciparum (malaria) - malaria is a protozoan transmitted by mosquitoes that infects red blood cells
  • Toxoplasma gondii (toxoplasmosis) - Toxoplasma gondii is an obligate intracellular protozoan that is present in cat feces. It can cause a mononucleosis-like syndrome.
Mycobacterium infections
  • Tuberculosis
Hematologic disorders
  • Leukemia and lymphoma - many leukemias and lymphomas cause lymphocytosis. Lymphocytes that are seen in malignancies tend to have similar sizes and shapes as opposed to other types of lymphocytosis that are often pleomorphic.
  • Monoclonal B lymphocytosis (MBL) - MBL is a precursor to chronic lymphocytic leukemia. It is defined as the presence of monoclonal B cells at levels < 5000 cells/μl without splenomegaly or other cytopenias. The prevalence of MLB increases with age, and it has been observed in up to 7% of patients > 60 years old with normal CBCs.
  • Congenital B cell lymphocytosis - congenital B cell lymphocytosis is a genetic disorder that affects CARD11, a scaffolding protein required for nuclear factor kappa B (NF-KB) in both B and T lymphocytes. Affected patients typically develop chronic lymphocytic leukemia by the fourth decade of life.
  • Persistent B-cell polyclonal B-lymphocytosis - persistent B-cell polyclonal B-lymphocytosis is a rare and poorly-understood condition predominantly seen in middle-aged female smokers. It is marked by polyclonal B cell expansion, the presence of circulating binucleated lymphocytes, and increased IgM serum levels.
  • Drug reactions with eosinophilia and systemic symptoms (DRESS) - DRESS is a syndrome caused by certain medications that can present with fever, rash, lymphadenopathy, facial swelling, organ system inflammation (e.g. hepatitis, nephritis, myocarditis), hematologic abnormalities (e.g. eosinophilia, lymphocytosis), and myositis. Atypical lymphocytes are also frequently present.
    • Drugs that have been associated with DRESS include the following:
      • Allopurinol (Zyloprim®)
      • Carbamazepine (Tegretol®)
      • Cenobamate (Xcopri™)
      • Clozapine (Clozaril®)
      • Eslicarbazepine (Aptiom®)
      • Lamotrigine (Lamictal®)
      • Febuxostat (Uloric®)
      • Leflunomide (Arava®)
      • Levetiracetam (Keppra®)
      • Olanzapine (Zyprexa®)
      • Oxcarbazepine (Trileptal®)
      • Phenobarbital
      • Phenytoin (Dilantin®)
      • Quetiapine (Seroquel®)
      • Sulfasalazine
      • Sulfonamides
      • Teriflunomide (Aubagio®)
      • Valproic acid (Depakote®)
      • Vancomycin
      • Zonisamide (Zonegran®)
      • Ziprasidone (Geodon®)
  • Epinephrine - epinephrine injections may cause a transient lymphocytosis that is followed by a neutrophilia
  • Post-transplant lymphoproliferative disorder (PTLD) - post-transplant lymphoproliferative disorder (PTLD) is a rare immune syndrome seen in organ transplant recipients that can range in severity from benign lymphocytosis to lymphoma. The majority of PTLD events appear related to Epstein-Barr Virus (EBV) infection, and patients who are seronegative for EBV are at greatest risk
  • Stress and trauma - physiologic stress from different medical events (e.g. myocardial infarction, seizures) can cause a transient lymphocytosis that is often followed by neutrophilia
  • Splenectomy - circulating lymphocytes may increase after splenectomy

  • Reference [16,17]
Diagnostic testing in lymphocytosis
  • Peripheral blood smear / Pathologist's review - the peripheral blood smear can help to identify a number of abnormalities. Atypical lymphocytes are seen in EBV infection, CMV infections, early HIV infection, Bartonella henselae infection, and DRESS syndrome. The presence of immature lymphocytes (e.g. blast cells) is concerning for malignancy. Certain conditions have characteristic findings (e.g. hairy cell leukemia).

  • Epstein-Barr testing
    • Heterophile antibody test (Monospot test) - the heterophile antibody test, also called monospot test, is an assay that detects heterophile antibodies in a sample of blood. Heterophile antibodies are antibodies produced in response to an EBV infection that crossreact with antigens on the erythrocytes of animals (e.g. sheep, horse) and cause agglutination. Monospot tests may be performed on blood from a venous sample or a fingerstick, in which case, rapid tests can give results in minutes. Monospot tests are highly specific but only have a sensitivity of 70 - 90%; in children under 4 years of age, the sensitivity falls to as low as 27%. Heterophile antibodies peak between 2 - 6 weeks after infection, so testing too early may lead to false-negative results. [18,19]
    • Epstein-Barr antibody tests - Epstein-Barr antibody tests are assays that detect antibodies that are specific to the EBV. This is in contrast to the monospot test which detects nonspecific heterophile antibodies. EBV antibody assays include the following: (1) Viral capsid antigen (IgM and IgG), (2) Early antigen (IgG), (3) EBV nuclear antigen. See EBV laboratory testing (CDC website) for more information on these tests.
    • Atypical lymphocytes - atypical lymphocytes, also called Downey cells, are one of the first signs of mononucleosis. Atypical lymphocytes are activated cytotoxic T cells that are enlarged and have irregular nuclei. These cells resemble monocytes on a peripheral smear and are the reason that the term "mononucleosis" was coined. Atypical lymphocytosis of at least 20% or atypical lymphocytosis of at least 10% and lymphocytosis of at least 50% are sometimes used as diagnostic criteria for mononucleosis. [20]

  • Flow cytometry - flow cytometry is a process where cells are passed individually in front of a laser. Light scattered from the laser is measured and used to tell different characteristics about the cell. Fluorescent reagents (e.g. conjugated antibodies, DNA binding dyes) that target specific cell components can also be added to the cells and measured during flow cytometry. In evaluating lymphocytosis, flow cytometry can be used to recognize cell surface markers (e.g. CD proteins) that identify what type of lymphocytes are present (B cell vs T cell) along with their maturity.

  • Fluorescence in situ hybridization (FISH) - FISH is a technique where fluorescent probes that attach to specific DNA sequences are used to detect certain genes in a sample of cells. FISH can be used to tell if lymphocytosis is monoclonal or polyclonal, and it can identify the presence of genes that are associated with lymphoproliferative disorders.

  • To convert cells/μl to cells/liter, multiply by 1000000. So 2500 cells/μl = 2.5 X 109 cells/L
  • Normal values may vary by lab
  • References [26,27,28]
Eosinophil levels in adults
Range Absolute eosinophil count
Severe eosinophilia > 5000
Moderate eosinophilia 1500 - 5000
Mild eosinophilia 500 - 1500
Normal 50 - 500
(1 - 3% of WBCs)
Eosinopenia < 50

  • Reference [27,28,29,30]
Causes of eosinophilia
Primary eosinophilia
  • Hematologic malignancies - eosinophilia that occurs in hematologic malignancies may be primary or secondary. If eosinophils are part of the neoplastic clone (e.g. chronic eosinophilic leukemia), the eosinophilia is considered primary or "clonal." If the eosinophils are not part of the neoplastic clone, and are instead a reaction to the neoplasm, they are considered secondary. Secondary eosinophilia is common with certain lymphomas (e.g. Hodgkin and non-Hodgkin lymphoma) and leukemias.

  • Systemic mastocytosis - mastocytosis is a condition where mast cells abnormally accumulate and proliferate inside of tissues. Cutaneous mastocytosis is the most common type of mastocytosis, and it is characterized by itchy skin rashes and plaques. Systemic mastocytosis is another form of the disease, and it is marked by mast cell accumulation in the skin, bone marrow, gastrointestinal tract, liver, and spleen. Eosinophilia that may be both clonal and reactive is often seen in systemic mastocytosis. The treatment of systemic mastocytosis is aimed at inhibiting the inflammatory mediators that mast cells release (e.g. histamine, bradykinin, etc.). Epinephrine, antihistamines, and corticosteroids are used to treat acute symptoms, and various immunosuppressive therapies have been used to treat aggressive disease. Stem cell transplantation may be curative in some patients.
Idiopathic eosinophilia
  • Idiopathic hypereosinophilic syndrome (HES) - idiopathic hypereosinophilic syndrome is a diagnosis of exclusion defined as eosinophilia (> 1500 cells/μl) for ≥ 6 months with evidence of end organ damage and no identifiable etiology of eosinophilia on workup. Organ damage in HES occurs from the release of eosinophilic granules that damage surrounding tissues. Involved organs include the heart, lungs, skin, peripheral and central nervous systems, and gastrointestinal tract. Affected patients also have a high risk of thromboembolism. The primary treatment of HES is corticosteroids. Refractory cases may be treated with imatinib, cyclosporine, interferon-alpha, and other immunosuppressants. HES is a rare syndrome, and in many cases, an alternative etiology (e.g. chronic eosinophilic leukemia) manifests itself during follow-up.
Secondary eosinophilia
Allergic conditions
  • Asthma
  • Atopic dermatitis/eczema
  • Seasonal allergic rhinitis
Autoimmune diseases
  • Eosinophilic fasciitis (Shulman disease)
  • Rheumatoid arthritis
  • Sarcoidosis
  • Systemic lupus erythematosus
Fungal infections
  • Aspergillosis - may be seen in patients with asthma, cystic fibrosis, and/or immunodeficiencies
  • Coccidioidomycosis - endemic to southwestern US and northern Mexico
  • Fascioliasis - comes from ingestion of water lettuce, mint, khat, and watercress grown in sheep-raising areas
Gastrointestinal disorders
  • Eosinophilic esophagitis
  • Chronic pancreatitis
  • Inflammatory bowel disease
  • Celiac disease
  • Anakinra (Kineret®)
  • Dupilumab (Dupixent®)
  • Inhaled corticosteroids - in rare cases, inhaled corticosteroid use has been associated with eosinophilia and Churg-Strauss Syndrome
  • Natalizumab (Tysabri®)
  • Drug reactions with eosinophilia and systemic symptoms (DRESS) - DRESS is a syndrome caused by certain medications that can present with fever, rash, lymphadenopathy, facial swelling, organ system inflammation (e.g. hepatitis, nephritis, myocarditis), hematologic abnormalities (e.g. eosinophilia, lymphocytosis), and myositis. Atypical lymphocytes are also frequently present.
    • Drugs that have been associated with DRESS include the following:
      • Allopurinol (Zyloprim®)
      • Carbamazepine (Tegretol®)
      • Cenobamate (Xcopri™)
      • Clozapine (Clozaril®)
      • Eslicarbazepine (Aptiom®)
      • Lamotrigine (Lamictal®)
      • Febuxostat (Uloric®)
      • Leflunomide (Arava®)
      • Levetiracetam (Keppra®)
      • Olanzapine (Zyprexa®)
      • Oxcarbazepine (Trileptal®)
      • Phenobarbital
      • Phenytoin (Dilantin®)
      • Quetiapine (Seroquel®)
      • Sulfasalazine
      • Sulfonamides
      • Teriflunomide (Aubagio®)
      • Valproic acid (Depakote®)
      • Vancomycin
      • Zonisamide (Zonegran®)
      • Ziprasidone (Geodon®)
  • Some malignancies may cause a reactive eosinophilia as opposed to a clonal or primary eosinophilia
  • Examples of these malignancies include the following:
    • Solid tumors (e.g. gastric and lung carcinomas cause a paraneoplastic eosinophilia)
    • Lymphomas (e.g. Hodgkin lymphoma, non-Hodgkin lymphoma)
    • Acute lymphoblastic leukemia
    • Adult T-cell leukemia
    • Human T-cell lymphotropic virus I (HTLV-I) infection
    • Systemic mastocytosis - can cause a reactive and clonal eosinophilia. See systemic mastocytosis above.
Parasitic infections
  • Helminth (worm) infections often cause eosinophilia. Eosinophils secrete factors that punch holes in parasites and cause them to die.
  • Parasitic infections associated with eosinophilia include the following:
    • Ancylostoma (Hookworm)
    • Ascariasis
    • Fascioliasis
    • Filariasis
    • Gnathostomiasis
    • Paragonimiasis
    • Schistosomiasis
    • Strongyloidiasis
    • Toxocariasis
    • Trichinosis
    • Visceral larva migrans
  • Polyarteritis nodosa - polyarteritis nodosa is a systemic vasculitis that affects medium and small arteries of the skin, joints, peripheral nerves, intestines, and kidneys.
  • Eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome) - Churg-Strauss syndrome is a systemic vasculitis that affects medium and small arteries of the lungs, heart, skin, kidneys, and peripheral nerves. Patients present with asthma, recurrent sinusitis, neuropathy, and eosinophilia. Forty percent of patients are positive for antineutrophil cytoplasmic antibodies (ANCA).
  • Atherosclerosis - some studies have found a direct correlation between eosinophil count and atherosclerosis
  • Gleich syndrome - Gleich syndrome is a rare disorder marked by recurrent episodes of urticaria, fever, angioedema, weight gain, and eosinophilia that occur 3 - 4 weeks apart
  • Graft-versus-host disease
  • Loffler syndrome - Loffler syndrome is a transient eosinophilia that occurs in response to helminth larvae when they pass through the lungs
  • Scabies
  • Wells syndrome - Wells syndrome is a rare dermatologic condition marked by recurrent granulomatous dermatitis with eosinophilia

  • References [27]
Steps in evaluating eosinophilia
Step 1 - check the following labs in all patients
  • CBC and peripheral smear
  • CMP - to assess for liver, kidney, and bone damage
  • Phosphate - to assess bone changes
  • LDH - to look for end-organ damage
  • C-reactive protein and ESR
  • Vitamin B12 level - elevated B12 levels can be a sign of myeloid disorders

  • Patients with eosinophilia of 500 - 1500 cells/μl and no concerning findings
    • Further testing may not be indicated

  • Patients with eosinophilia > 1500 cells/μl and/or concerning findings
    • Proceed to Step 2
Step 2 - consider the following based on patient history
  • Allergies
    • Serum total immunoglobulin E (IgE)
    • Allergen-specific IgE tests
    • Skin-prick testing for specific allergies
  • Dermatologic findings (e.g.mastocytosis)
    • Skin biopsy
  • Infections
    • Helminths - stool for ova and parasites, ELISA serology testing
    • Fungal infections - lung imaging, cultures, serology
    • HIV and HTLV-1 testing
  • Gastrointestinal causes
  • Autoimmune disorders
  • Vasculitis
    • Antineutrophil cytoplasmic antibodies (ANCA)
    • Hepatitis B, Hepatitis C, HIV, cytomegalovirus (CMV) and parvovirus B19 testing
  • Malignancy
    • Bone marrow biopsy
    • Imaging and tissue biopsy
  • Other
    • Atherosclerosis - imaging or cardiac testing
    • Gleich syndrome - Immunoglobulins and C1 esterase levels
Step 3 - if testing and/or history is not revealing, refer to heme/onc for hematologic malignancy and HES testing

  • Reference [31,32]
Causes of basophilia
Spurious basophilia
  • Hematology analyzers used to perform CBCs often do not give accurate basophil counts. Basophilia should be confirmed with a peripheral smear, and if necessary, flow cytometry which is the most precise method.

Reactive basophilia
  • Known causes
    • Allergic conditions (atopy) - basophilia from allergic conditions often occurs with eosinophilia, and the basophil count typically does not exceed 1000 cells/μl
    • Iron deficiency - iron deficiency has been associated with basophilia
    • Diabetes - diabetics have been shown to have a higher number of circulating basophils, and diabetic ketoacidosis may cause an acute increase
  • Possible causes
    • Autoimmune disorders
    • Chicken pox
    • Cirrhosis
    • Drug reactions
    • Influenza
    • Inflammatory bowel disease
    • Tuberculosis

Hematologic disorders
  • Chronic myeloid leukemia (CML) - persistent basophilia, especially > 1000 cells/μl, is the most common CBC abnormality seen in CML
  • Primary myelofibrosis and myelodysplasia
  • Acute myeloid leukemia
  • Chronic and acute basophilic leukemias
  • Polycythemia vera
  • Essential thrombocythemia
  • Chronic myelomonocytic leukemia
  • Lymphoma

  • References [16,17,33]
Causes of monocytosis
Reactive monocytosis
  • Autoimmune diseases
    • Inflammatory bowel disease
    • Rheumatoid arthritis
    • Sarcoidosis
    • Systemic lupus erythematosus
  • Hematologic disorders
    • Neutropenia (from any cause) - monocytosis may be a compensatory reaction to neutropenia
    • Sickle cell disease
    • Hemolytic anemia
    • Immune thrombocytopenia
  • Infections
    • Bacterial endocarditis
    • Brucellosis
    • Epstein-Barr virus
    • Fungal infections (e.g. Aspergillosis)
    • Malaria
    • Protozoan infections (e.g. Giardia, Cyclospora)
    • Rickettsial infections (e.g. Rocky Mountain spotted fever)
    • Syphilis
    • Tuberculosis
  • Medications / Therapy
    • Corticosteroids
    • Radiation therapy
    • Ziprasidone (Geodon®)
  • Other
    • Chronic stress
    • Myocardial infarction
    • Postsplenectomy
    • Solid tumors (e.g. ovarian, gastric, lung)
Primary monocytosis
  • Chronic myelomonocytic leukemia (CMML) - CMML is the most likely neoplasm to present with an absolute monocytosis of > 1000 cells/μl
  • Juvenile myelomonocytic leukemia
  • Acute myeloid leukemia with monocytic differentiation
  • Chronic myeloid leukemia
  • Myelodysplastic syndromes

  • HL - hodgkin lympnoma
  • Reference [35,36]
Hodgkin Lymphoma Stages
Stage Finding
I One of the following:
  • HL cell found in a single lymph node region (this can include one node or a group of adjacent nodes)
  • HL cells found in one lymphoid organ (e.g. thymus)
  • HL cells found in 1 part of 1 organ outside the lymph system
II One of the following:
  • HL cells found in two or more lymph node regions on the same side of the diaphragm
  • HL cells found in a lymph node area and a nearby organ outside the lymphatic system (on the same side of the diaphragm)
III One of the following:
  • HL cells found in lymph node regions on both sides of the diaphragm
  • HL is in lymph nodes above the diaphragm and in the spleen
  • HL cells have spread widely into one or more organs outside the lymphatic system such as the liver, bone marrow, or lungs
Other findings that may be used to further stage Hodgkin lymphoma include:
  • A vs B - the stage may be either A or B. A means "B symptoms" are not present, and B means they are present. See symptoms above.
  • Bulky disease - bulky disease means tumors in the chest that are at least 1/3 as wide as the chest, or tumors in other areas that are at least 10 centimeters (about 4 inches) across. It's usually labeled by adding the letter X to the stage. It's especially important for stage II lymphomas, because bulky disease may require more intensive treatment.

  • Reference [35,36]
Non-Hodgkin Lymphoma Stages
Stage Finding
I One of the following:
  • The lymphoma is in only 1 lymph node area or lymphoid organ such as the tonsils (I)
  • The cancer is found only in 1 area of a single organ outside of the lymph system (IE)
II One of the following:
  • The lymphoma is in 2 or more groups of lymph nodes on the same side of (above or below) the diaphragm
  • The lymphoma is in a group of lymph node(s) and in one area of a nearby organ (IIE)
III One of the following:
  • The lymphoma is in lymph node areas on both sides of the diaphragm
  • The lymphoma is in lymph nodes above the diaphragm, as well as in the spleen
  • The lymphoma has spread widely into at least one organ outside the lymph system, such as the bone marrow, liver, or lung
Stage categories:
  • E - stands for "extranodal." It means the lymphoma extends to an area or organ beyond the lymphatic system.
  • S - stands for spleen and it means the lymphoma is found in this organ
  • X - indicates “bulky disease.” This is a nodal mass whose greatest size is usually more than 10 cm or more than one third of the chest diameter by x-ray.

  • Reference [35,36]
Revised International Staging System (RISS) Stages
Stage Finding
I All of the following:
  • Serum beta-2 microglobulin < 3.5 mg/L
  • Albumin level ≥ 3.5 g/dL
  • No high-risk cytogenetic features
  • LDH level is normal
  • Not stage I or III
III Serum beta-2 microglobulin > 5.5 mg/L and one of the following:
  • High-risk cytogenetics
  • Elevated LDH