Upper limit of normal ALT levels in health and metabolic diseases: Pooled analysis of 423,355 individuals with bootstrap modelling

Introduction: Given the global rise in obesity-related metabolic diseases, the upper limit of normal (ULN) alanine aminotransferase (ALT) in individuals with and without metabolic diseases may have changed. We performed a meta-analysis combined with bootstrap modelling to estimate the ALT ULN levels for individuals with and without metabolic diseases. Methods and Results: Two separate searches of the PubMed, Embase and Cochrane databases were performed, one to identify healthy individuals which yielded 12 articles (349,367 individuals); another to include those with potential metabolic diseases but without known liver disease which yielded 35 articles (232,388 individuals). We estimated the mean ALT using a random-effects mixed model and the ULN level (95th-percentile value) via a bootstrap model with 10,000 resamples. In individuals without metabolic diseases and known liver disease, the ALT ULN levels were 32 U/L overall; 36 U/L in males and 28 U/L in females. In analyses that included individuals with metabolic diseases, the ALT ULN levels were 40 U/L among the overweight/obese (29 U/L if normal weight) and 36 U/L among those with type 2 diabetes mellitus (T2DM) (33 U/L if no T2DM). On meta-regression of study-level factors, body mass index (coefficient 1.49, 95% CI 0.11-2.86, p = 0.03), high-density lipoprotein (coefficient -0.47, 95% CI -0.85-(-0.08), p = 0.02) and triglycerides (coefficient 0.19, 95% CI 0.12-0.25, p < 0.0001) correlated with ALT. Conclusion: We provide expected ranges of ALT ULN levels for individuals without known liver disease without metabolic diseases and those with or without T2DM and/or are normal weight or overweight/obese. These data may have implications for clinical care and screening.