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Organic Acids, Qualitative, Urine

Organic Acids, Qualitative, Urine

Test Summary

Organic Acids, Qualitative, Urine

  

Clinical Use

  • Screen for organic acidurias

Clinical Background

Organic acidurias are inherited disorders resulting from a deficient enzyme or transport protein. Although most are autosomal recessive disorders, several are X-linked. The more than 60 described organic acidurias affect many metabolic pathways including amino acid metabolism, lipid metabolism, purine and pyrimidine metabolism, the urea cycle, the Krebs cycle, and fatty acid oxidation. These disorders are characterized by a wide variety of symptoms such as lethargy, coma, hypotonia, seizures, ataxia, vomiting, failure to thrive, developmental delay, liver disease, neutropenia, thrombocytopenia, osteomalacia, and osteoporosis. Severity of presentation is highly variable as is age of onset, and patients may not present with the most characteristic features. Laboratory results commonly indicate metabolic acidosis, increased anion gap, hyperammonemia, hypoglycemia, lactic acidemia, ketosis, or abnormal lipid patterns. Treatment may be based on dietary restrictions and/or supplementation with cofactors (eg, riboflavin or cobalamin) or conjugating agents (eg, carnitine or sodium benzoate); however, there is no effective therapy for some of the disorders.

Individuals Suitable for Testing

  • Infants

  • Children

  • Adults

Method

  • Gas chromatography/mass spectrometry

  • Qualitatively assesses 63 organic acids

  • Reported results: normal or increased and a patient-specific interpretation

  • Turn-around-time: 4-6 days

Interpretive Information

This test screens for organic acids that are at least moderately increased. Positive results should be confirmed using the quantitative urinary organic acid test (test code 38067). This screen may miss disorders characterized by minimal or intermittent metabolite excretion, especially if the patient is asymptomatic at the time of sample collection. Additionally, the following metabolites are poorly extracted from urine and may result in a missed diagnosis: 2-methylacetoacetic acid, 3-hydroxyisovaleric acid, 4-hydroxybutyric acid, glutaconic acid, glyoxylic acid, mevalonic acid, pyruvic acid, and suberylglycine.

Elevations of single or multiple organic acids are associated with specific organic acidurias (Table).

Table. Selected Organic Acidurias and Associated Organic Acid Elevations

Organic Aciduria

Elevated Organic Acid
Methylmalonic acidemia

Methylmalonic acid, methylcitric acid,
3-hydroxypropionic acid, propionylglycine,
3-hydroxyvaleric acid

Fatty oxidation defects (medium chain
acyl-CoA dehydrogenase deficiency [MCAD])

Adipic acid, suberic acid, sebacic acid, suberylglycine, hexanoylglycine, phenylpropionylglycine

Propionic acidemia

Propionylglycine, methylcitric acid,
3-hydroxypropionic acid, 3-hydroxyvaleric acid

Glutaric aciduria, type 1

Glutaric acid, glutaconic acid, 3-hydroxyglutaric
acid

Multiple acyl-CoA dehydrogenase deficiency
(glutaric aciduria, type II)

Glutaric acid, adipic acid, suberic acid,
2-hydroxyglutaric acid, ethylmalonic acid, isovalerylglycine

Isovaleric acidemia

Isovalerylglycine, 3-hydroxyisovaleric acid

Multiple carboxylase deficiency

3-Methylcrotonylglycine, methylcitric acid, lactic acid, 3-hydroxyisovaleric acid, tiglylglycine,
3-hydroxypropionic acid

Urea cycle defects

Orotic acid

Maple syrup urine disease (MSUD)

2-Oxoisocaproic acid, 2-hydroxyisocaproic acid,
2-hydroxyisovaleric acid, 2-oxoisovaleric acid,
2-hydroxy-3-methylvaleric acid, 2-oxo-3-methylvaleric acid

Lactic acidosis

Lactic acid, pyruvic acid, 2-hydroxybutyric acid,
4-hydroxyphenyllactic acid

Tyrosinemia

4-Hydroxyphenyllactic acid, 4-hydroxyphenylacetic acid, 4-hydroxyphenylpyruvic acid, N-acetyltyrosine, succinylacetone (type I only)

Canavan disease

N-acetylaspartic acid

Ketosis

Acetoacetic acid, 3-hydroxybutyric acid, adipic acid, suberic acid, 3-hydroxyisobutyric acid,
3-hydroxyisovaleric acid, 3-hydroxy-2-methylbutyric acid

Phenylketonuria (PKU)

Phenyllactic acid, phenylpyruvic acid,
2-hydroxyphenylacetic acid

3-Hydroxy-3-methylglutaric aciduria

3-Hydroxy-3-methylglutaric acid,
3-hydroxyisovaleric acid, 3-methylcrotonylglycine, 3-methylglutaconic acid, 3-methylglutaric acid

3-Methylcrotonyl-CoA carboxylase deficiency

3-Hydroxyisovaleric acid, 3-methylcrotonylglycine

3-Methylglutaconic aciduria

3-Methylglutaconic acid, 3-hydroxyisovaleric acid,
3-methylglutaric acid

3-Oxothiolase deficiency

3-Hydroxy-2-methylbutyric acid, tiglylglycine (±), acetoacetic acid, 3-hydroxybutyric acid

Alkaptonuria

Homogentisic acid

5-Oxoprolinuria

5-Oxoproline

Dihydrolipoyl dehydrogenase deficiency
(lipoamide dehydrogenase, E3)

Lactic acid, 2-hydroxyisocaproic acid,
2-hydroxyisovaleric acid, 2-hydroxy-3-methylvaleric acid, 2-oxoglutaric acid, 2-oxoisocaproic acid,
2-oxoisovaleric acid, 2-oxo-3-methylvaleric acid

References

  1. Part 9, Organic Acids. In Scriver CR, Beaudet AL, Sly WS, et al, eds. The Metabolic and Molecular Basis of Inherited Disease. 8th ed. New York, NY: McGraw-Hill, Inc; 2001:2109-2260.

  2. Kushnir MM, Komaromy-Hiller G. Rapid screening for urine organic acids by GC-MS. Clin Chem. 1999;45:A2.
     

Content reviewed 12/2011
 
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