Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (687 page)

   Less than 100 U/L in alcoholic cirrhosis; ALT is normal in 50%, and AST is normal in 25% of these cases.

   Less than 150 U/L in alcoholic hepatitis (may be higher if the patient has delirium tremens).

   Less than 200 U/L in approximately 50% of patients with cirrhosis, metastatic liver disease, lymphoma, and leukemia.

   Normal values may not rule out liver disease: ALT is normal in 50%, and AST is normal in 25% of cases of alcoholic cirrhosis.

   Degree of increase has a poor prognostic value.

   Serial determinations reflect clinical activity of liver disease. Persistent increase may indicate chronic hepatitis.

   Mild increase of AST and ALT (usually <500 U/L) with ALP increased greater than three times normal indicates cholestatic jaundice, but more marked increase of AST and ALT (especially >1,000 U/L) with ALP increased less than three times normal indicates hepatocellular jaundice.

   Rapid decline in AST and ALT is a sign of recovery from disease but in acute fulminant hepatitis may represent loss of hepatocytes and poor prognosis.

   Poor correlation of increased concentration with extent of liver cell necrosis and has a little prognostic value.

   Although AST, ALT, and bilirubin are most characteristic of acute hepatitis, they are unreliable markers of severity of injury.

   ALT has 45% variation during the day; highest in afternoon and lowest at night. Both AST and ALT exhibit 10–30% variation from 1 day to next. AST levels are 15% higher in African American men.

AMMONIA (BLOOD NH
₃
, NH
₃
, NH
₄
)

   Definition

   Ammonia is derived mostly from protein degradation. Most of the ammonia in the blood comes from the intestine, where colonic bacteria use ureases to breakdown urea to ammonia and CO
₂
. Eight-five percent of blood from the intestine is carried directly to the liver via the portal vein and 85% of ammonia is converted back to urea and excreted by the kidneys and colon.
Helicobacter pylori
in the stomach appears to be an important source of ammonia in patients with cirrhosis.