Prevalence of neutropenia in the US population: Age, sex, smoking status, and ethnic differences

Background: Benign reductions in neutrophil counts may be more common at certain ages and in certain ethnic groups and may be affected by sex and smoking status. Objective: To determine differences in neutrophil counts in the U.S. population according to ethnicity, age, sex, and smoking status. Design: Population-based, cross-sectional study. Setting: Various locations in the United States. Participants: 25 222 participants in the 1999 to 2004 National Health and Nutrition Examination Survey who were 1 year of age or older. Measurements: Complete blood counts and comparison of means and the proportion of participants with neutropenia. Results: Relative to white participants, black participants had lower leukocyte counts (mean difference, 0.89 x 10(9) cells/L; P < 0.001), lower neutrophil counts (0.83 x 10(9) cells/L; P < 0.001), and similar lymphocyte counts (0.022 x 10(9) cells/L; P = 0.36), whereas Mexican-American participants had slightly higher mean leukocyte counts (0.16 x 10(9) cells/L; P = 0.014), higher neutrophil counts (0.11 x 10(9) cells/L; P = 0.026), and higher lymphocyte counts (0.095 x 10(9) cells/L; P < 0.001). The prevalence of neutropenia (neutrophil count < 1.5 x 10(9) cells/L) was 4.5% among black participants, 0.79% among white participants, and 0.38% among Mexican-American participants. The prevalence of neutropenia was higher among males and children younger than 5 years of age. Neutrophil counts less than 1.0 x 10(9) cells/L were observed in fewer than 1% of the overall sample (0.57% in black participants, 0.11% in white participants, and 0.08% in Mexican-American participants). Smoking was associated with higher leukocyte and neutrophil counts but had a smaller effect among black and Mexican-American participants than among white participants. Limitation: Because estimates are based on single measures, fluctuations over time could not be determined. Conclusions: In the United States, neutrophil counts are lower in black persons than in white persons and neutropenia is more prevalent in black persons. Neutrophil counts are slightly higher in Mexican -American persons than in white persons, and neutropenia is uncommon in both groups. The clinical implications of these findings are unclear, but they suggest that when determining the need for a diagnostic evaluation for neutropenia, clinicians should consider the patient's age, sex, ethnicity, and smoking status.