- Portosystemic shunting (PSS).
- Inborn error of metabolism (IEM).
- Secondary hyperammonemia is caused by inborn errors of intermediary metabolism characterised by reduced activity in enzymes that are not part of the urea cycle (e.g. .Propionic acidemia, Methylmalonic acidemia) or dysfunction of cells that make major contributions to metabolism (e.g. hepatic failure).
- Idiopathic hyperammonemia (IHA) is a medical condition in which increased levels of ammonia are disproportional to liver dysfunction without the presence of an inherited metabolic disorder. Other conditions that may elevate ammonia production involve herpes infection, multiple myeloma, urinary diversion or infection with organisms that split urease enzyme. A person is unlikely to suffer from this condition unless there is some type of defect in the metabolic conversion system. In newborns, the defect often results from genetic defects. In older adults, however, the defect mostly occurs due to a diseased liver. However, onset of genetic disorders of the urea cycle in a growing number of adults is also being seen as a reason.
- Certain physiologic stressors cause stress and arouse hyperammonemia in sufferers of metabolic disorders. These agents include dietary changes, fever, Pneumonia, Pregnancy, infection with urease-splitting organisms, GI bleeding and upper respiratory tract illnesses.
- Urinary orotic acid tests: The level is increased markedly in OTC deficiency and mildly in other enzyme deficiencies except for CPS/NAGS deficiency, in which it is decreased mildly.
- Urinary ketone tests: Presence of ketosis indicates an organic acidemia.
- Plasma and urinary organic acid tests: These levels screen for the presence of an organic acidemia that may be causing the hyperammonemia.
- Enzyme assays: Assays performed on tissue specimens obtained by percutaneous liver biopsy can determine diagnosis in cases of CPS, NAGS, and OTC deficiency. Enzyme assays are also performed on red blood cells (for arginase deficiency), fibroblast from skin biopsy (argininosuccinate synthetase (ASS), Argininosuccinate lyase (ASL), and hyperornithinemia, hyperammonemia, and homocitrillinemia (HHH)), and intestinal mucosa (CPS, OTC). Enzyme analysis has largely been replaced by genetic analysis. It is still indicated in selected cases with negative genetic testing or if genetic testing is not available.
- Glutamine and alanine levels are increased in all urea cycle defects except for arginase deficiency.
- Citrulline level is decreased mildly in CPS/NAGS and OTC deficiencies but increased markedly in AS deficiency and moderately in AL deficiency.
- Arginine level is increased markedly in arginase deficiency but decreased mildly in all the other enzyme deficiencies of the urea cycle.
- Argininosuccinic acid level is increased markedly in AL deficiency.
- Allopurinol loading test: This test establishes the carrier status of women at risk for OTC deficiency. After a loading dose of allopurinol, urinary orotidine excretion is measured; it is increased greatly in carriers.
- DNA analysis: Several techniques are available to determine the presence of a mutation at the OTC locus.
- MR spectroscopy: This shows an elevated glutamine/glutamate peak coupled with decreased myoinositol and choline signals.[18, 19]
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