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Test ID: ALAD    
Aminolevulinic Acid Dehydratase (ALAD), Whole Blood

Useful For Suggests clinical disorders or settings where the test may be helpful

Confirmation of a diagnosis of aminolevulinic acid dehydratase deficiency porphyria

 

This test will not detect lead intoxication.

Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request

Aminolevulinic acid dehydratase (ALAD) activity can be inhibited in situations including hereditary tyrosinemia type 1, lead intoxication, and exposure to styrene, trichloroethylene, or bromobenzene. These causes should be ruled out when considering a diagnosis of ALAD deficiency porphyria.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Porphyrias are a group of inherited disorders resulting from enzyme defects in the heme biosynthetic pathway. Aminolevulinic acid (ALA) dehydratase (ALAD) deficiency porphyria (ADP) results from a deficiency of ALAD, which causes ALA accumulation with subsequent excretion in the urine. Urinary porphobilinogen (PBG) remains essentially normal, which rules out other forms of acute porphyria.

 

ADP is an autosomal recessive, acute hepatic porphyria that produces neurologic symptoms similar to those seen in acute intermittent porphyria. Symptoms include acute abdominal pain, peripheral neuropathy, nausea, vomiting, constipation, and diarrhea. Respiratory impairment, seizures, and psychosis are possible during an acute period. ADP is extremely rare with only 7 cases described in the literature since 1979.

 

The workup of patients with a suspected porphyria is most effective when following a stepwise approach.

 

See Porphyria (Acute) Testing Algorithm in Special Instructions or contact Mayo Medical Laboratories to discuss testing strategies.

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.

Reference ranges have not been established for patients who are <16 years of age.

 

> or =4.0 nmol/L/sec

3.5-3.9 nmol/L/sec (indeterminate)

<3.5 nmol/L/sec (diminished)

Interpretation Provides information to assist in interpretation of the test results

Abnormal results are reported with a detailed interpretation including an overview of the results and their significance, a correlation to available clinical information provided with the specimen, differential diagnosis, and recommendations for additional testing when indicated and available, and a phone number to reach a laboratory director in case the referring physician has additional questions.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This assay is not useful in assessment of lead intoxication as it reactivates aminolevulinic acid dehydratase (ALAD) that has been inhibited by lead. The preferred test for lead toxicity is PBBD / Lead with Demographics, Blood.

 

Abstinence from alcohol is essential for at least 24 hours prior to specimen collection as ethanol suppresses ALAD activity.

 

False-positive values may result from enzyme degradation due to improper specimen handling. It is essential to adhere to instructions outlined in the Specimen Required and the Specimen Stability Information fields.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Tortorelli S, Kloke K, Raymond K: Chapter 15: Disorders of porphyrin metabolism. In Biochemical and Molecular Basis of Pediatric Disease. Fourth edition. Edited by DJ Dietzen, MJ Bennett, ECC Wong. AACC Press 2010, pp 307-324

2. 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

3. Anderson KE, Sassa S, Bishop DF, Desnick RJ: Disorders of heme biosynthesis: X-linked sideroblastic anemia and the porphyrias. In The Metabolic Basis of Inherited Disease. Eighth edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company, 2001, pp 2991-3062

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test