Liver enzymes are frequently tested for the assessment of patients with a range of diseases. They are traditionally, used to provide evidence on whether a patient’s primary disorder is hepatitic or cholestatic in origin. Nevertheless, information of enzyme ratios and pattern recognition offers much more information from the results of these simple tests.

Mounting evidences suggest that liver enzyme ratios can predict the severity of certain diseases. The chronic form of the rare genetic disorder Wilson’s disease with both hepatic and neurological presentation is typified by a mild liver enzyme alteration. All these tests, namely bilirubin, AST level and prothrombin time can classify patients on the basis of disease severity using the Nazer score, which can help clinicians in formulating the correct management approach.

On the other hand, these liver enzymes have limitation in diagnosis cirrhosis in patients with chronic viral hepatitis B or C, as majority cases of cirrhosis show normal alanine transaminase (ALT). The key role of ALT in viral hepatitis is the monitoring of anti-viral treatment. Researchers also demonstrated that aspartate transaminase (AST):ALT ratio >1 suggests cirrhosis, which is considered a poorly sensitive test, however specificity of this ratio in diagnosing cirrhosis reaches over 99% when used in combination with a platelet count of <150,000/mm³ and other variables, such as prothrombin time. Besides, the AST: platelet ratio index (APRI), another useful indicator of cirrhosis in hepatitis patients, is limited by its poor sensitivity.  An APRI >1.5 indicates moderate to severe fibrosis. 

The International Autoimmune Hepatitis (AIH) Group guidelines state that a predominant serum transaminase abnormality, in association with a GGT of >1.5 times normal, is suggestive of AIH when combined with autoantibody and histological data, and when all other causes have been excluded. Although liver enzymes are not a successful diagnostic tool for predicting the presence or absence of cirrhosis, a constant rise in transaminases >10 fold, or >5 fold in relation to a twofold rise in gamma-glutamyl transferase (GGT), is suggestive of a higher mortality which further requires aggressive treatment.

Thus, liver enzymes can assist in the initiation of treatment, monitoring of response, remission and relapse, and help making decisions to stop treatment when enzymes have normalised for a prolonged period. Moreover, continued higher levels of transaminases, even in the presence of therapy is indicative of a high risk of disease progression to cirrhosis and hepatocellular carcinoma, along with higher risk of recurrence of disease following liver transplantation.

Source: Hall P, Cash J. What is the real function of the liver function tests?. Ulster Med J. 2012;81(1):30-36.