A patient may present with clinical encephalopathy and an elevated plasma ammonia concentration. While often related to underlying liver disease, this pattern can be seen in a number of disorders. It may not be suspected and so go unrecognized unless a plasma ammonia is ordered for some other reason.


Clinical and laboratory features:

(1) reduced level of consciousness

(2) elevated plasma ammonia concentration


Liver disease:

(1) cirrhosis with portal hypertension

(2) other causes of portal hypertension

(3) Reye's syndrome


Inherited metabolic disorders (especially the urea cycle enzyme defects):

(1) argininosuccinic acid lyase deficiency (ASAL)

(2) lysinuric protein intolerance (LPI)

(3) hyperammonemia-hyperornithinemia-homocitrullinemia syndrome (HHH)

(4) citrullinemia (argininosuccinic acid synthetase or ASA deficiency)

(5) argininemia (arginase deficiency)

(6) carbamylphosphate synthetase I or N-acetylglutamate synthetase (CPS/NAGS)

(7) organic acidopathies


Oncologic conditions:

(1) multiple myeloma and other hematopoietic conditions

(2) cytoreductive chemotherapy

(3) bone marrow transplant



(1) valproic acid

(2) asparaginase (? effect on aspartate)


Infection related:

(1) urinary tract infection

(2) ureterosigmoidostomy-related rectocolitis



(1) transient hyperammonemia of the newborn (TNH, THAN)

(2) excessive intake of essential amino acids


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