Need for validation of clinical decision aids: use of the AST/ALT ratio in predicting cirrhosis in chronic hepatitis C.

OBJECTIVE: A value of > or = 1 for the ratio of aspartate amino-transferase to alanine aminotransferase (the AST/ALT ratio or AAR) has been shown to have a positive predictive value of 100% for the diagnosis of cirrhosis in patients with chronic hepatitis C. If validated on separate cohorts, an AAR > or = 1 might obviate the need for liver biopsy in some patients with hepatitis C.
METHODS: We attempted to validate the AAR by abstracting demographic and clinical data from a database of consecutive patients with hepatitis C who had a liver biopsy between 1993 and 1998. We used definitions, methods of data collection, and analyses comparable to those of the published study. A hepatopathologist blindly reviewed 49 liver biopsies for histological grade and stage.
RESULTS: The current cohort of 177 patients and the previous cohort of 139 patients were comparable in mean age (42.3 vs 43.8 yr), percentage of men (63 vs 67), percentage with an AAR > or =1 (20 vs 17), and Child-Pugh distribution, but differed in substantial use of ethanol (11% vs 3.6%; p = 0.01) and in the prevalence of cirrhosis (23% vs 34%, p = 0.06). Respective sensitivities of the AAR were 56% and 53%. An AAR > or =1 had a positive predictive value of 64% (95% confidence interval 48-78%) for the current cohort. Thirteen of 36 patients (36%) with an AAR > or =1 were incorrectly identified as having cirrhosis. Of these 13 patients, 6 had a normal AST and ALT, 5 had a minimally elevated AST or ALT, and 1 had advanced fibrosis without cirrhosis.
CONCLUSIONS: These results suggest that an AAR > or =1 may not be as useful for predicting cirrhosis in chronic hepatitis C as previously thought, and emphasizes the need for validation of clinical decision aids on independent patient cohorts.