AMINO ACIDS - urine

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Specimen: Random urine.

Method: Qualitative - chromatography or high voltage electrophoresis. Quantitative - HPLC.

Reference Interval: Varies with age and amino acid.

Application: Suspected metabolic genetic disease with psychomotor regression (eg phenylketonuria, homocystinuria), acute CNS or metabolic abnormality (eg non-ketotic hyperglycinaemia, maple syrup urine disease), bone disease (hypophosphatasia), renal calculi (cystinuria) or failure to thrive (Fanconi syndrome).

Interpretation: Many non-specific abnormalities occur with non-genetic metabolic diseases. These may mimic the abnormalities of genetic diseases eg elevated tyrosine is found in all patients with hepatic failure, and urine tyrosine cannot be used to diagnose type I tyrosinaemia. Amino acids are present in urine in excessive amounts:

(i)	if the plasma concentration is excessive (eg phenylketonuria)
(ii)	if renal tubular reabsorption is impaired (eg Fanconi syndrome).

Reference: Edwards MA et al. Ann Clin Biochem 1988; 25: 129-141.

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