Is benign constitutional neutropenia a stable low neutrophil count without added infection risk?

Benign constitutional neutropenia (BCN) is a well-characterized hematologic condition where individuals maintain an absolute neutrophil count (ANC) lower than standard laboratory reference ranges without associated health risks. It is frequently observed in individuals of African, Middle Eastern, and West Indian ancestry, often linked to the Duffy-null phenotype (ACKR1 genetic variant).

Clinical and diagnostic evidence

Clinical evidence confirms that BCN typically presents as a mild-to-moderate neutropenia—usually with ANC levels between 0.5 and 1.5 × 10⁹/L—that is discovered incidentally during routine blood work.

• Persistent stability: Unlike acquired forms of neutropenia, BCN is characterized by its long-term stability. Guidelines from the European Hematology Association (EHA) indicate that monitoring CBC trends over a period of 3 to 6 months is standard to confirm the absence of a progressive decline or the emergence of other cytopenias (such as anemia or thrombocytopenia).
• Infection risk: Despite lower circulating neutrophil counts, individuals with BCN do not exhibit an increased frequency or severity of infections. Clinical data from various cohorts show that these individuals respond normally to inflammatory challenges, and the neutropenia does not lead to the clinical complications typically associated with bone marrow failure or autoimmune disorders.
• Diagnostic approach: Confirmation relies heavily on the clinical context, including the patient’s ethnic background and the lack of physical findings like splenomegaly or lymphadenopathy. If the ANC remains stable and the patient is asymptomatic, invasive procedures such as bone marrow biopsies are generally unnecessary.

Mechanistic explanations

The benign nature of this condition is explained by the redistribution of neutrophils rather than a production defect in the bone marrow.

• Neutrophil partitioning: In individuals with the Duffy-null phenotype, the lack of the Duffy antigen (ACKR1) on red blood cells affects how neutrophils circulate. Mechanistic studies suggest that these neutrophils may not marginate (stick to vessel walls) in the same way as in Duffy-positive individuals.
• Tissue availability: Instead of circulating in the blood, a larger proportion of the total body neutrophil pool resides in the tissues and the spleen. Because the marrow production remains intact and the functional pool is available, the body can rapidly mobilize these cells into the bloodstream during an acute infection or stress, maintaining full immunocompetence.

Bottom line

Benign constitutional neutropenia is a stable, non-pathological condition that does not cause recurrent infections. Diagnosis is confirmed by observing stable CBC trends over several months and assessing the patient's clinical and ethnic context to avoid unnecessary and invasive medical investigations.