Low Prevalence of Asymptomatic Neutropenia in Thailand.

The prevalence and etiology of asymptomatic neutropenia in Asians are still unknown. Therefore, we conducted the epidemiologic study to survey the frequency and related factors of neutropenia in general Thai population.

Blood samples from healthy Thai citizens resided in Bangkok and 4 provinces from different areas were collected from October 2008-May 2009. Absolute neutrophil count (ANC) < 1.50 ×10⁹/l was used as the cut-off point for neutropenia.^[1]

Six thousand nine hundred and seventy one samples were analyzed. There were 2,422 male and 4,549 female. The median age was 49 years (range 15-93 years). The subjects from Bangkok (n=4,297) are younger and are more commonly male compared to those from non-urban areas (n=2,674) (p<0.01). The overall mean white blood cell count (WBC) and ANC were 7.57±4.07 ×10⁹/l (mean ± 2SD) and 4.18 ±3.05 ×10⁹/l (mean ± 2SD), respectively. The prevalence of neutropenic cases were 0.43% (30 cases, 95%CI 0.41-0.44). The mean percentage of the circulating neutrophil count was 54.58±17.25% (mean ± 2SD). It was notable that 1.87% of the participants had the circulating WBC ≥ 12.6 ×10⁹/l. There was no influence of age, sex or survey sites on the prevalence of neutropenia. The neutropenia subjects defined as ANC lower than 2SD of the studied populations (1.13 ×10⁹/l) were only 8 cases (0.11%). The prevalence of cases, which ANC < 1.0 and 0.5 ×10⁹/l, were 0.03% and 0% respectively.

The frequency of asymptomatic neutropenia in Thai was 0.43% defined by ANC < 1.50 ×10⁹/l. Compared with the previous largest population report^[1], the prevalence were lower than that of American white (0.79%, 95%CI 0.57-1.01), African American (4.47%95%CI 3.92-5.02) and similar to Mexican American (0.38%, 95%CI 0.24-0.52). The underlying cause of these racial discrepancies remains to be explored.

[1] Hsieh MM, Everhart JE, Byrd-Holt DD, Tisdale JF, Rodgers GP. Prevalence of neutropenia in the U.S. population: age, sex, smoking status, and ethnic differences. Ann Intern Med. 2007 Apr 3;146(7):486-92.

No relevant conflicts of interest to declare.