GPT and viral hepatitis: However, data from a series of patients with acute liver injury as a result of viral hepatitis suggest that the most sensitive and specific aminotransferase threshold level to identify acute injury lies within the moderate range of increase (5 to 10 times the upper reference limit, at 200 U/L for AST [sensitivity 91%, specificity 95%] and 300 U/L for ALT [sensitivity 96%, specificity 94%]).8