Serum transaminase levels (GGT, aspartate aminotransferase [AST], and alanine aminotransferase [ALT]) should be checked because elevations are suggestive of hepatitis. Values in the hundreds of units per liter are consistent with viral inflammation, but elevations into the thousands suggest hepatocellular necrosis, extensive liver injury, and more fulminant disease. In acute and chronic viral hepatitis, the ratio of AST to ALT is usually less than 1, whereas a ratio greater than 2 is more suggestive of alcoholic hepatitis. Serum alkaline phosphatase level also should be determined; if elevated more than 3-fold above normal, cholestasis should be suspected (a concurrently elevated GGT supports this suspicion). Total serum bilirubin level and its direct fraction also may be useful because a conjugated (direct) fraction of 30% or higher is consistent with viral hepatitis. The magnitude of transaminase elevation is not a reliable marker of disease severity, but a persistent total bilirubin level above 20 milligrams/dL or a PT prolonged by more than a few seconds or elevated INR indicates significant liver dysfunction and a poor prognosis. Serum electrolytes, BUN, and creatinine levels should be checked if there is clinical suspicion of volume depletion or electrolyte abnormalities. Abnormal mental status should prompt an immediate determination of serum glucose level, which may be low due to poor oral intake or hepatic failure. Other causes of abnormal mental status such as hypoxia, sepsis, intoxication, structural intracranial process, or encephalopathy must be considered. A CBC may be useful because an early transient neutropenia followed by a relative lymphocytosis with atypical forms is often seen with viral hepatitis. Anemia, if present, may be more suggestive of alcoholic hepatitis, decompensated cirrhosis, GI bleeding, or a hemolytic process. Serologic studies to determine the specific viral agent responsible may be ordered in the emergency department to facilitate the final diagnosis, but these results are rarely immediately available. Acetaminophen levels should be checked if concern of toxic ingestion exists. The differential diagnosis includes viral hepatitis, alcohol- or toxin-induced hepatitis, medication effects, infectious mononucleosis, cholecystitis, ascending cholangitis, sarcoidosis, lymphoma, liver metastases, and pancreatic or biliary tumors.