Table 1.

Differential diagnosis of neurometabolic disorders presenting as acute encephalopathy

Biochemical investigation	Urea cycle disorders	Maple syrup urine disease	Organic acidurias	Fatty acid oxidation defects	Nonketotic hyperglycinemia
Metabolic acidosis	not present	variably present	present +++	variably present	not present
Plasma glucose	normal	normal or decreased ↓	decreased ↓↓	decreased ↓↓↓	normal
Urinary ketones	normal	elevated ↑↑	elevated ↑↑	absent	normal
Plasma ammonium	elevated ↑↑↑	normal	elevated ↑↑	elevated ↑	normal
Plasma lactate	normal	normal	elevated ↑	variable	normal
Liver function tests	normal	normal	normal	liver enzymes elevated	normal
Plasma amino acids	abnormal	↑ branched chain amino acids	↑ glycine	normal	↑ glycine
Urinary organic acids	normal	abnormal	abnormal	abnormal	normal
Plasma carnitine	normal	normal	abnormal	abnormal	normal