What does a mildly low white blood cell count indicate in this Black male patient with an absolute neutrophil count of 2.10 ×10⁹/L and a normal differential?

Benign Ethnic Neutropenia

In this Black male patient with an ANC of 2.10 × 10⁹/L and a normal differential, the mildly low WBC most likely represents benign ethnic neutropenia (BEN), a normal physiological variant that requires no intervention and does not increase infection risk.

Understanding the Context

This patient's ANC of 2.10 × 10⁹/L falls well within the established reference ranges for individuals of African descent. The most recent and specific evidence demonstrates that Duffy-null individuals (predominantly those of African ancestry) have a lower reference interval for ANC with a lower bound of 1.01 × 10³/µL 1. Your patient's value of 2.10 is comfortably above this threshold.

The Genetic Basis

Approximately 25-50% of persons of African descent carry the Duffy-null polymorphism (rs2814778), which causes constitutively lower neutrophil counts 2, 3. This is not a pathological condition but rather a normal variant that:

• Does not increase susceptibility to infection
• Requires no treatment or monitoring
• Reflects adequate bone marrow reserve that responds appropriately when needed 2

Race-Specific Reference Ranges

The traditional neutropenia threshold of 1.5 × 10⁹/L is inappropriate for Black patients. Population-based data shows:

• Adult Black males have a 2.5th percentile ANC of 1.3 × 10⁹/L 4
• The prevalence of ANC <1.5 × 10⁹/L is 4.5% in Black individuals versus 0.79% in White individuals 5
• Nearly all Black patients (93%) who test positive for Duffy-null phenotype have lower baseline counts 6

Clinical Implications

No workup is indicated for this patient given:

1. ANC is 2.10 × 10⁹/L (well above the race-specific lower limit)
2. Normal differential (no left shift, no immature forms)
3. Asymptomatic presentation
4. Black ethnicity

The evidence clearly shows that hematologic disorders are rare in patients with mild neutropenia, particularly among Black patients 6. In one study, only 23% of referred patients had clinically relevant outcomes, and these occurred at a mean ANC of 0.59 × 10⁹/L—far below your patient's value 6.

Common Pitfall to Avoid

The major pitfall is unnecessary hematology referral and bone marrow evaluation based on race-inappropriate reference ranges. This leads to:

• Disproportionate referral of Black patients for benign findings 6
• Patient anxiety and healthcare costs
• Potential exclusion from clinical trials or treatment protocols that use outdated neutropenia thresholds

When to Investigate Further

Consider actual pathological neutropenia only if:

• ANC drops below 1.0 × 10⁹/L 2, 1
• Patient develops recurrent infections
• Abnormal differential appears (left shift, dysplasia, blasts)
• Progressive decline in serial counts
• Associated cytopenias in other cell lines

For this specific patient: document as benign ethnic neutropenia, reassure the patient, and avoid unnecessary follow-up or referral.