Approach to Nonmalignant Leukopenia and Leukocytosis
Hematology · Approach to Nonmalignant Leukopenia and Leukocytosis 🎯 Practice these cards
Because leukocyte reference ranges span the mean ± ____ SD, roughly ____% of healthy people fall outside the standard range by chance alone.
Leukocyte reference ranges span two standard deviations around the population mean, so normal biologic variation alone produces out-of-range results in a predictable minority — about 2.5% of healthy persons will have a count above or below the standard range. Most abnormal leukocyte counts are not malignant.
Neutropenia is defined as an ANC below ____/µL, and severe neutropenia is defined as an ANC below ____/µL.
Neutropenia is defined as an absolute neutrophil count (ANC) below 1500/µL, and severe neutropenia as an ANC below 500/µL. Clinical risk is determined not by the count alone but by the depth of neutropenia, bone marrow reserve, and comorbid conditions; complications become more common as the ANC falls.
Lymphopenia is defined as an ALC below ____/µL; a chronically low ALC with recurrent infections should prompt evaluation for ____ and measurement of immunoglobulin levels.
Lymphopenia (absolute lymphocyte count <1000/µL) can be a response to glucocorticoids and other medications or to a variety of bacterial and viral infections. A chronically low ALC accompanied by recurrent infections should prompt evaluation for immunodeficiency, including measurement of immunoglobulin levels. Lymphopenia without clinical consequences or an associated illness does not require treatment.
Nutritional causes of neutropenia include deficiencies of vitamin B12, folate, and ____; neutropenia can also result from cellular redistribution with sequestration in an enlarged spleen due to ____.
Neutropenia can result from impaired marrow production, immune-mediated destruction, or cellular redistribution — especially sequestration in an enlarged spleen from portal hypertension due to cirrhosis or portal vein thrombosis. Nutritional causes include vitamin B12, folate, and copper deficiencies (cobalamin and folate often with macrocytic anemia; copper deficiency is rare but responds to supplementation).
Classic drugs that cause neutropenia include the antibiotic ____, the antipsychotic ____, and the antithyroid agents methimazole and propylthiouracil.
Common medications causing neutropenia include antibiotics (trimethoprim-sulfamethoxazole, dapsone, vancomycin), psychiatric agents (clozapine, tricyclic antidepressants), immunomodulators (methotrexate, azathioprine, tacrolimus, mycophenolate), and thyroid drugs (methimazole, propylthiouracil). Mechanisms include impaired granulopoiesis and drug-dependent antibody-mediated destruction of neutrophils.
Drug-induced neutropenia typically appears within the first ____ months of drug initiation, occurs most often in patients older than ____ years, and symptoms usually improve within 1 to 3 weeks of stopping the offending agent.
Medication-induced neutropenia occurs most often in patients older than 50 years and typically appears within the first 3 months of drug initiation. It is often reversible: treatment centers on stopping the offending agent, and symptoms usually resolve within 1 to 3 weeks. G-CSF can shorten recovery time and may be used in patients with neutropenia and active infection.
Benign ethnic neutropenia is now termed Duffy-null–associated neutrophil count: it results from homozygosity for the ____ (DARC) rs2814778 variant producing the Fy(a−b−) phenotype, and ASH 2023 endorsed ____-based (race-neutral) ANC reference ranges.
The low ANC once attributed to race is largely genetic: homozygosity for the ACKR1 (DARC) rs2814778 variant produces the Duffy-null phenotype Fy(a−b−), carried by roughly two-thirds of many Black/African-ancestry populations. In 2023, the American Society of Hematology designated "Duffy-null–associated neutrophil count" as the preferred term over "benign ethnic neutropenia" and endorsed genotype-based (race-neutral) ANC reference ranges. The condition causes a chronically low ANC (typically 1000–1500/µL) but does not increase infection frequency or severity and requires no treatment.
Duffy-null healthy Black adults have a median ANC of about ____/µL versus 5000/µL in Duffy-positive individuals, and nearly one-quarter have an ANC below ____/µL that would be labeled neutropenia under standard ranges.
In one study of healthy Black adults, Duffy-null individuals had a median ANC of about 2800/µL versus 5000/µL in Duffy-positive individuals, and nearly one-quarter had an ANC <2000/µL — values that would be labeled "neutropenia" under standard ranges and could trigger unnecessary workups or chemotherapy dose delays. The Fy(a−b−) phenotype identifies these individuals far more accurately (~97% sensitive, ~96% specific) than self-identified race (~66%/49%).
Monoclonal B-cell lymphocytosis is a monoclonal B-cell population below ____/µL that does not meet criteria for ____; about 1–2% per year of patients with clone sizes above 2000/µL progress, and management is periodic monitoring without intervention.
Monoclonal B-cell lymphocytosis (MBL) refers to a monoclonal population of B lymphocytes (<5000/µL) that does not meet criteria for chronic lymphocytic leukemia (CLL) or another lymphoproliferative malignancy; it is usually detected incidentally in asymptomatic patients. Approximately 1% to 2% of patients with a clone size greater than 2000/µL evolve to meet CLL criteria each year; smaller clones carry a much lower risk and normal longevity. No intervention is required, but patients should be monitored periodically for signs of progression.
In a 2024 MBL study, the epigenetic and immunogenetic signature ____ identified a high-risk subgroup with a progression probability of about ____% at 5 years and 71% at 10 years, outperforming the CLL-IPI for time to first therapy.
Current practice for high-count MBL remains surveillance (periodic CBC and clinical follow-up, no treatment). A 2024 study of 219 individuals with MBL showed that a combined epigenetic and immunogenetic signature — ELCLV3-21, incorporating IGLV3-21 usage — identified a high-risk subgroup with a progression probability of about 40% at 5 years and 71% at 10 years, and predicted time to first therapy better than the CLL-IPI (c-statistic 0.77 vs 0.67).
Common causes of neutrophilia include bacterial infections, ____ use, and cigarette smoking; smoking-associated neutrophilia may persist for ____ after cessation.
Neutrophilia frequently accompanies bacterial infections and acute/chronic inflammatory states, and can be caused by medications including glucocorticoids, lithium, myeloid growth factors, and catecholamines. Other causes include asplenia, obesity (especially in women), physical/emotional stressors, and cigarette smoking — mechanism unknown — with the effect often persisting for years after smoking cessation.
In acute EBV infection, reactive/____ lymphocytes on the peripheral smear may be mistaken for circulating ____; the smear should be interpreted in clinical context before raising concern for acute leukemia.
Acute Epstein-Barr virus infection can present with lymphadenopathy, hepatosplenomegaly, and an elevated ALC; its reactive/atypical lymphocytes may be mistaken for blasts on the peripheral smear. Interpret the smear in clinical context before raising concern for acute leukemia. Lymphocytosis accompanies many viral processes (EBV, CMV, HIV, influenza) and some bacterial infections (pertussis, cat scratch disease, C. difficile).
Monocytosis accompanies infections such as ____; monocytosis persisting more than ____ months without an obvious infectious explanation, particularly with cytopenias, should prompt referral to evaluate for a possible hematopoietic stem cell disorder.
Monocytosis is often reactive and accompanies some infections such as tuberculosis. Persistent monocytosis lasting more than 6 months without an obvious infectious explanation — particularly when associated with cytopenias such as anemia or thrombocytopenia — should be referred for evaluation of possible hematopoietic stem cell disorders.
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