Upper normal threshold of serum alanine aminotransferase in identifying individuals at risk for chronic liver disease.

Background/Aims Serum alanine aminotransferase (ALT) is an easily available, low-cost screening tool for detecting silent chronic liver disease. Recent studies have suggested that the currently accepted healthy ALT thresholds be lowered. Methods In this retrospective cross-sectional study, we determined upper thresholds for ALT values in a nationally representative healthy cohort (n=3337) from the Fourth Korea National Health and Nutrition Examination Survey (KNHANES IV). Sensitivity and specificity of the currently used ALT threshold (40 IU/L, regardless of gender) was compared against study-derived, gender-specific ALT thresholds for detecting individuals at risk for chronic liver disease in 27913 health check-up participants. Results The 95th percentile levels for ALT in healthy weight, metabolically normal, liver disease-free KNHANES participants were 34IU/L for men and 25IU/L for women. The prevalence of ALT elevation among health check-up participants was 11.0% in currently used thresholds, and increased to 22.6% with study-derived, gender-specific thresholds. Of the population who were additionally defined to have elevated ALT levels under new ALT threshold, 65.7% were at risk for chronic liver disease. Sensitivity for detecting individuals at risk for chronic liver disease improved from 18 to 33% with new thresholds whereas a trade-off in specificity (from 96 to 88%) was observed. Conclusions It is recommendable to lower the current ALT thresholds to better identify individuals at risk for chronic liver disease.