Suggested guidelines for the diagnosis and management of urea cycle disorders

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

Parameter	Condition
	UCDs	Organic acidurias	β-Oxidation defects	Hyperinsulinism- hyperammonemia syndrome	Pyruvate carboxylase deficiency^g
Acidosis	+/–	+ ^e	+/–	–	+
Ketonuria ^a	–	+	–	–	++
Hypoglycemia ^b	–	+/–	+	+	+
↑ Lactic acid ^c	–	+	+/–	–	+
↑ AST & ALT	(+)^d	–	+	–	+/–
↑ CPK	–	–	+	–	–
↑ Uric acid	–	+	+	–	–
↓ WBC/RBC/Plt	–	+	–	–	–
Weight loss	–	+^f	–	–	+

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.
Grade of recommendation, D.
^a In neonates ketonuria (++ or +++) suggests organic aciduria.
^b Hypoglycemia and hyperammonemia (“pseudo-Reye”) can be predominant manifestations of the organic aciduria due to 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.
^c Blood lactate >6mmol/L, since lower high lactate levels (2-6mM) may be due to violent crying or to extensive muscle activity.
^d AST & ALT elevations can be found but are not constant in UCDs.
^e Can be absent in neonates.
^f Occurrence only in neonates.
^g Only type B is associated with hyperammonemia but not types A and C.

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