Answer is A (Prothrombin time (PT)): An increased prothrombin time is the most frequently observed first laboratory test suggesting the possibility of hepatocellular failure. Early liver failure may be suspected based on isolated prolongation of the Prothrombin Time (PT). Patients with early hepatocellular failure may present with isolated prolongation of PT Prolonged PT is an early sensitive indicator of hepatic synthetic dysfunction due to the sho half life offactor VII (2-6 hours) vvhich the failing liver cannot maintain. APTT is prolonged after PT in Liver Disease. Albumin has a long half life of about 20 days and hence reduced albumin will manifest only after 20 days of onset of Reduced synthetic function of Liver. Increased aerial ammonia is also a sign of acute liver failure, however increased aerial ammonia is primarily vieved as an impoant factor in the development of hepatic encephalopathy. 'Patient with liver disease may have only a prolonged PT (normal APTT and thrombin time) reflecting a decrease in factor VII which is the. first to be reduced in liver disorders because of its sho half life of 2-6 hours' 'Factor Vila is an essential enzyme in the extrinsic pathway of coagulation. The pathway is evaluated by PT. Because factor VII has the shoest half life of the procoagulant proteins, patient with early liver disease may present with an isolated prolonged PT' - Hematology / Oncology Secrets / 82 `Increased Prothrombin Time has a high prognostic value, paicularly for patients with acute hepatocellular failure. An abnormal prothrombin lime with confirmed prolongation of more than 5-6 seconds above control is the single laboratory test that draws attention to the possibility of the development offlummant hepatic necrosis (acute hepato cellular failure) in the course of acute viral hepatitis. Such a prolonged prothrombin time often precedes by days the manifestations of liver failure' - Schiff's Disease of the Liver 1011/52 'Most coagulation factors are produced in the liver (except VWF) and development of liver disease may result in prolongation of both PT and APTT. However because factor VII (Extrinsic pathway; measured by PT) has the shoest half life amongst all vitamin K dependent factor. PT will be the first to be prolonged. Development of Liver disease will lead to deficiency offactor VII first and initial prolongation of only the Prothrombin Time. With fuher deterioration of liver function both the PT and APTT will be prolonged' - 'Clinical Anesthesia' by stoelting (Lippincott Williams) 2009/396