Amino acids - urine

Last updated: Wednesday, 07, April, 2004

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Item Process
Specimen

Random urine.

Advise the laboratory about current drug therapy.

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

Clinical details are critical for relevant 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 Bioche. 1988; 25: 129-141.

Shih VE. In: Blau N et al. Physician's guide to the laboratory diagnosis of metabolic diseases. Chapman and Hall Medical 1996.