Aminolevulinic Acid (ALA), Urine
Assistance in the differential diagnosis of the various porphyrias
An indicator of lead intoxication in children
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Aminolevulinic acid (ALA) is formed by the reaction of succinyl-coenzyme A with glycine, which is catalyzed by ALA synthase. This reaction is the first step in the biosynthesis of heme, and is followed by the conversion of ALA to porphobilinogen by ALA dehydratase. End products of heme synthesis are hemoglobin, myoglobin, and the cytochromes, which consist of 4 pyrrole rings connected by methylene bridges and complexed with iron.
The excretion of ALA can be increased either due to inherited deficiencies of enzymes involved in the heme biosynthetic pathway (ALA dehydratase deficiency porphyria, acute intermittent porphyria, hereditary coproporphyria, variegate porphyria) or due to secondary inhibition of ALA dehydratase. Among the secondary causes, acute lead intoxication causes the highest degree of aminolevulinic aciduria. Less significant elevations include chronic lead intoxication, tyrosinemia type I, alcoholism, and pregnancy. For additional information on the recommended order of testing, see Porphyria (Acute) Testing Algorithm and Porphyria (Cutaneous) Testing Algorithm in Special Instructions.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
<1 year: < or =10 nmol/mL
1-17 years: < or =20 nmol/mL
> or =18 years: < or =15 nmol/mL
Elevated values are found in several inherited and acquired conditions that are characterized by various degrees of aminolevulinic aciduria:
-Aminolevulinic acid dehydratase deficiency porphyria
-Acute intermittent porphyria
-Intoxication with lead and other heavy metals
-Tyrosinemia type I
-Alcoholism and alcohol induced hepatitis
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
The differential diagnosis of aminolevulinic aciduria must be considered on the basis of the patient's clinical presentation.
The preferred test for lead toxicity in children is blood lead (see PBBD/15070 Lead with Demographics, Blood).
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Meyer UA, Schuurmans MM, Lindberg RL: Acute porphyrias: pathogenesis of neurological manifestations. Semin Liver Dis 1998;18:43-52
2. Warren MJ, Cooper JB, Wood SP, Shoolingin-Jordan PM: Lead poisoning, haem synthesis and 5-aminolaevulinic acid dehydratase. Trends Biochem Sci 1998;23:217-221
3. Anderson KE, Sassa S, Bishop DF, et al: Disorders of heme biosynthesis: X-linked sideroblastic anemia and the porphyrias. In The Metabolic Basis of Inherited Disease. 8th edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Medical Publishing Division, 2001, pp 2991-3062
4. Nuttall KL, Klee GG: Analytes of Hemoglobin Metabolism-Porphyrins, Iron, and Bilirubin. In Tietz Textbook of Clinical Chemistry. Fifth edition. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 2001, pp 584-607