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Table 2 Bedside differential diagnosis of inborn errors of metabolism presenting with hyperammonemia

From: Suggested guidelines for the diagnosis and management of urea cycle disorders

Parameter Condition
  UCDs Organic acidurias β-Oxidation defects Hyperinsulinism- hyperammonemia syndrome Pyruvate carboxylase deficiencyg
Acidosis +/– + e +/– +
Ketonuria a + ++
Hypoglycemia b +/– + + +
↑ Lactic acid c + +/– +
↑ AST & ALT (+)d + +/–
↑ CPK +
↑ Uric acid + +
↓ WBC/RBC/Plt +
Weight loss +f +
  1. In addition to the conditions indicated in the table, mitochondrial oxidative phosphorylation defects, citrin deficiency, lysinuric protein intolerance or ornithine aminotransferase deficiency can also cause hyperammonemia.
  2. Grade of recommendation, D.
  3. a In neonates ketonuria (++ or +++) suggests organic aciduria.
  4. b Hypoglycemia and hyperammonemia (“pseudo-Reye”) can be predominant manifestations of the organic aciduria due to 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.
  5. c Blood lactate >6mmol/L, since lower high lactate levels (2-6mM) may be due to violent crying or to extensive muscle activity.
  6. d AST & ALT elevations can be found but are not constant in UCDs.
  7. e Can be absent in neonates.
  8. f Occurrence only in neonates.
  9. g Only type B is associated with hyperammonemia but not types A and C.