Ammonia Tolerance in Assessing the Patency of Portacaval Anastomoses

Five hundred four serial ammonia tolerance tests (ATTs) were performed before and after portacaval anastomoses (PCA) in 71 cirrhotic patients with and without PCA. These patients had similar in the type, duration, severity, and signs of cirrhosis. Baseline ATT results were similar in both groups. Subsequent ATT values in the control group remained unchanged; in the shunt group, ATT values became more abnormal. In 41 patients the shunts were proved to be patent and in 8 to be occluded. Increments in ammonia intolerance more than 20% above preshunt levels were found in 75% of patients with patent PCA and in 33% of those with occluded shunts. The ATT is a useful screening test but is not sufficiently precise for accurate diagnosis.