Determination of reference intervals for serum complement C3 and C4 levels in Chinese Han ethnic males.

Background: Clinical laboratory reference intervals (RIs) for serum complement C3 and C4 levels have been established in many countries but there is a lack of published data regarding normal ills in Chinese population. We attempted to establish ills for serum complement C3 and C4 levels in Chinese Han ethnic males. Methods: A total of 1,234 healthy male subjects, aged 20 - 69 years, were collected from the Fangchenggang Area Male Health and Examination Survey (FAMHES). Serum complement C3 and C4 levels were measured by immunoturbidimetry. The two-sided 95-percentile RIs were calculated using parametric statistical methods. Results: Serum C3 values showed normal distribution and C4 were log-normal distributed. The two-sided 95% ills (mean +/- 2 SD) for serum C3 and C4 were 0.656 - 1.52 g/L and 0.181 - 0.561 g/L, respectively. Body Mass Index (BMI) had a significant positive association with C3 (r = 0.342) and C4 (r = 0.258), and age had a significant positive association with C4 (r = 0.117). No significant difference was found either between smoking groups or drinking groups. A significant increase with BMI was found both for C3 (p <0.001) and C4 (p < 0.001). BMI-specific ills were also calculated. Conclusions: The RIs for serum C3 and C4 show a slight deviation compared to previously reported reference levels. BMI-specific reference values should be implemented in clinical laboratories.