Influence of body mass index, sex and age on serum alanine aminotransferase (ALT) level in healthy blood donors

Background and aim: Serum alanine aminotransferase (ALT) level is the most common screening test as part of a routine evaluation of liver damage. In order to determine the factors influencing this liver function test in normal subjects, the relationship between ALT level and gender, age and body mass index (BMI) was studied in a large population of healthy blood donors. Methods: This population included 9,420 volunteer blood donors (4,488 men and 4,932 women aged from 18 to 70 years) selected on the basis of negative answers to a detailed medical questionnaire including past medical history, drug and alcohol consumption, on the absence of clinical signs of liver disease, on the negativity of serological testing for hepatitis B and C virus and HIV. Results: In the overall population, the mean serum ALT value was 21.8 I.U./L and the mean BMI was 24.4 kg/m2. There was a positive significant correlation between serum ALT level and BMI (Pearson r = 0.54 ; p < 0.001) and between ALT and age (Pearson r = 0.25 ; p < 0.001). A major sex-difference in ALT value was observed, the mean ALT value being higher in men than in women (26.8 ± 13.6 vs. 17.2 ± 8.1 I.U./L, p < 0.0001). In both sexes, ALT level was significantly correlated with BMI (Pearson r = 0.45 in men and r = 0.37 in women; p < 0.001). In women a consistent rise in BMI and ALT value with increasing age was observed whereas in men BMI and ALT level only increased with age up to the fifth decade. In conclusion, there was a significant positive correlation between ALT and BMI regardless the gender in a population of healthy volunteer blood donors. Moreover, at the same age and the same BNH, ALT was significantly lower in women than in men suggesting that the normal range for ALT value should be adjusted for gender. So gender and BNH have to be considered in the interpretation of ALT values.