Diurnal variation in serum alanine aminotransferase activity in the US population

Serum alanine aminotransferase (ALT) activity has been reported to be greater in the afternoon than the early morning, but data are scarce. We examined diurnal variation of ALT in a national population-based sample.

Participants in the 1999 to 2008 US National Health and Nutrition Examination Survey were randomly assigned to morning (AM; n = 4474 adolescents, 11,235 adults) or afternoon/evening (PM; n = 4887 adolescents, 11,735 adults) examinations. We examined ALT distributions graphically and compared both geometric mean ALT and the prevalence of elevated ALT, defined as >31 IU/L for adolescent boys, >24 IU/L for adolescent girls, >43 IU/L for adult men, and >30 IU/L for adult women, between AM and PM examination groups.

The examination groups were similar with the exception in the AM group of a longer fasting time and slightly higher prevalence of diabetes among adolescents and viral hepatitis B among adult women. ALT distributions were similar between examination sessions among the 4 groups. Among adolescents and men, neither mean ALT nor prevalence of abnormal ALT differed by examination group. Among women, mean ALT was statistically significant, but minimally higher in the PM group (19.6 IU/L) than the AM group (19.1 IU/L; P = 0.009). Among 1 subgroup, women with chronic viral hepatitis, there was a higher prevalence of abnormal ALT in the PM group (P = 0.018 in unadjusted analysis). Adjusting for liver injury risk factors had little effect on the difference in mean ALT.

In general, clinically significant diurnal variation in ALT activity was not found in the US population.