Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (688 page)

   
Normal range:
<50 μmol/L.

   Use

   In the diagnosis of hepatic encephalopathy and hepatic coma in the terminal stages of liver cirrhosis, hepatic failure, acute and subacute necrosis, and Reye syndrome. Hyperammonemia in infants may be an indicator of inherited deficiencies of the urea cycle metabolic pathway.

   Should be measured in cases of unexplained lethargy and vomiting, encephalopathy, or any neonate with unexplained neurologic deterioration.

   Not useful to assess the degree of dysfunction (e.g., in Reye syndrome, hepatic function improves and the ammonia level falls, even in patients who finally die of these disorders).

   Interpretation

Increased In

   Certain inborn errors of metabolism (e.g., defects in urea cycle, organic acid defects).

   Transient hyperammonemia in newborn; unknown etiology; may be life threatening in the first 48 hours.

   May occur in any patient with severe liver disease (e.g., acute hepatic necrosis, terminal cirrhosis, and after portacaval anastomosis). Increased in most cases of hepatic coma but correlates poorly with degree of encephalopathy. Not useful in known liver disease but may be useful in encephalopathy of unknown cause.

   Moribund children: Moderate increases (≤300 μmol/L) without being diagnostic of a specific disease.

   GU tract infection with distention and stasis.

   Ureterosigmoidostomy.

   Some hematologic disorders, including acute leukemia and after bone marrow transplantation.