Table 1

Explanation of metabolic tests done in figure 1

TestCondition it looks for
Urine metabolic screen
 Urine organic acidsOrganic acidaemias and maple syrup urine disease
Abnormal profiles may be present all the time or only during metabolic decompensation. Many substances may create artifactual changes including concomitant valproate administration
 Urine amino acidsDisorders of amino acid metabolism (eg, tyrosinaemia)
 Urine oligosaccharidesLooking for oligosaccharidoses (eg, mannosidosis and fucidosis)
 Urine mucopolysaccharidesLooking for elevated levels of glycosaminoglycans in mucopolysaccharidoses
LactateGluconeogenesis, pyruvate metabolism and respiratory chain mitochondrial disorders
May be raised artificially if child is struggling, or if the sample is haemolysed, CSF lactate is more specific
UrateLow: disorder of purine metabolism and molybdenum cofactor deficiency
High: several inborn error of metabolisms (eg, Lesch–Nyhan syndrome and glycogen storage disorders)
VLCFA+phytanic acidPeroxisomal disorders (eg, Zellweger syndrome)
CarnitineAn acylcarnitine profile is combined with measurement of free carnitine and picks up most fat oxidation disorders and some organic acidaemias
DisialotransferrinUsually performed as transferrin isoelectric focusing to look for CDGs, also more often known as congenital disorders of glycosylation
BiotinidaseBiotinidase deficiency, easily treated with biotin
LeadConsider if child lives in an old house or may be ingesting lead-containing paint
White cell enzymesLysosomal storage disorders