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By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.
Synopsis: Higher incidence of benign leukopenia from lower neutrophil counts is found in black persons compared to white in the United States, and Mexican-Americans and smokers have slightly higher routine counts.
Source: Hsieh MM, et al. Ann Intern Med. 2007;146:486-492.
White blood cell counts were analyzed from 25,222 participants in the National Health and Nutritional Examination Survey (NHANES) conducted from 1999-2004 and were analyzed by age, sex, ethnicity and smoking status. The survey consists of an interview, examination and laboratory data. A complex sampling strategy, including oversampling of under-represented groups to ensure accuracy, makes this representative of 253.2 million non-institutionalized U.S. residents. The threshold for neutropenia was defined as 1.5 x 109 cells/L as established by the National Cancer Institute.
Black participants had lower mean leukocyte and netrophil counts, with similar lymphocyte counts, compared to whites. Mexican-Americans had slightly higher counts of all types. Normal values for persons older than 18 years follow a bell-shaped curve for all ethnic groups, but blacks had a downward shift of approximately 1.0 x 109 for both leukocyte and neutrophil counts. The overall prevalence of neutropenia in blacks was 4.5%, compared to 0.8% for whites and 0.4% for Mexican-Americans. For black males the percentage was higher at 6.65% compared to 3.57% for black females. For 89% of the neutropenia in blacks, values were between 1.0-1.5 x 109.
Smokers in all ethnic groups had a higher overall mean leukocyte and neutrophil count than non-smokers, with an increase of 1.38 and 0.87 x 109 respectively, but blacks showed less of an increase than whites, and Mexican-Americans demonstrated the least effect.
Elimination of racial and ethnic disparities in health is a major national goal, and we need more information about normal variations to help us understand those disparities. Multiple past reports have documented asymptomatic or benign reductions of neutrophil counts in several ethnic groups, eg, Bedouin Arabs, Ethiopian or Yemeni Jews, and persons of African descent. Hematologic analyses have shown normal bone marrow cellularity and normal subpopulations of other leukocyte types, without increased risk for infections.1
Early analysis of neutropenia in black children led to a belief that nutritional deficiency might be the cause, but multiple studies now over 3 decades and in several different locations lead more to a conclusion of "benign ethnic neutropenia." The extensive NHANES data in this study adds support for a genetic etiology since the finding is so widespread, and other variations were seen in the reverse direction in Mexican-Americans.
The effect of smoking on leukocyte and neutrophil counts is thought to be due to an inflammatory response, possibly contributing to increased atherosclerosis and bronchial disease. All of these significant differences in what we understand as "normal" should lead us to be much more aware of the individual when we interpret laboratory results.2
1. Shoenfeld Y, et al. Arch Intern Med. 1982;142:797-799.
2. van der Vaart H, et al. Thorax. 2004;59:713-721.