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Test Catalog

Test ID: PBALP    
Porphobilinogen and Aminolevulinic Acid, Plasma

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

An equivalent option to urine for first-line test for evaluation of a suspected acute porphyria

 

Monitoring patients undergoing treatment for an acute intermittent porphyria or other acute porphyria

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

This test is used as part of the diagnostic assessment and monitoring of patients with acute intermittent porphyria (AIP) and other acute porphyrias.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

The following algorithms are available in Special Instructions:

-Porphyria (Acute) Testing Algorithm

-Porphyria (Cutaneous) Testing Algorithm

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

The porphyrias are a group of inherited disorders resulting from enzyme defects in the heme biosynthetic pathway. Depending on the specific enzyme involved, various porphyrins and their precursors accumulate in different specimen types. The patterns of porphyrin accumulation in erythrocytes and plasma, and the excretion of the heme precursors in urine and feces allow for the detection and differentiation of the porphyrias.

 

The porphyrias are typically classified as erythropoietic or hepatic based upon the primary site of the enzyme defect. In addition, of the 5 hepatic porphyrias, 4 typically present with acute neurological manifestations and are designated the acute porphyrias. Clinically, however, these attacks can be prolonged and chronic.

 

Three primary acute hepatic porphyrias: acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP), are associated with neurovisceral symptoms which typically onset during puberty or later. Common symptoms include severe abdominal pain, peripheral neuropathy, and psychiatric symptoms. A broad range of medications (including barbiturates and sulfa drugs), alcohol, infection, starvation, heavy metals, and hormonal changes may precipitate crises. Photosensitivity is not associated with AIP, but may be present in HCP and VP.

 

Plasma porphobilinogen (PBG) and aminolevulinic acid (ALA) are elevated during the acute phase of these neurologic porphyrias. Urine and fecal porphyrin analysis should be performed to confirm the diagnosis and to distinguish among AIP, HCP, and VP. A biochemical diagnosis of AIP can be confirmed by measurement of PBG deaminase activity (PBGD_ / Porphobilinogen Deaminase, Whole Blood). VP and HCP can be confirmed by measurement of fecal porphyrins (FQPPS / Porphyrins, Feces). Once the biochemical diagnosis of an acute porphyria is established, molecular genetic testing is available for AIP (HMBSZ / HMBS Gene, Full Gene Analysis), HCP (CPOXZ / CPOX Gene, Full Gene Analysis), or VP (PPOXZ / PPOX Gene, Full Gene Analysis) which allows for diagnosis of at-risk family members.

 

The very rare (<10 cases described) autosomal recessive aminolevulinic acid dehydratase deficiency porphyria (ADP) is also a primary acute porphyria causing neurovisceral symptoms. It presents in childhood and biochemically, it is characterized by an isolated significant elevation of aminolevulinic acid (ALA). More commonly, however, isolated elevations of ALA are due to secondary inhibition of ALA dehydratase. Among the secondary causes, acute lead intoxication results in the highest degree of aminolevulinic aciduria. Less significant elevations are seen in chronic lead intoxication and tyrosinemia type I.

 

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

 

The following algorithms are available in Special Instructions or call 800-533-1710 to discuss testing strategies:

-Porphyria (Acute) Testing Algorithm

-Porphyria (Cutaneous) Testing Algorithm

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.

Porphobilinogen: < or =0.5 nmol/mL

Aminolevulinic Acid: < or =0.5 nmol/mL

Interpretation Provides information to assist in interpretation of the test results

Abnormal results are reported with a detailed interpretation that may include an overview of the results and their significance, a correlation to available clinical information provided with the specimen, differential diagnosis, recommendations for additional testing when indicated and available, and a phone number to reach one of the laboratory directors 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

Additional testing must be performed to distinguish among the acute porphyrias.

 

The specimen should be collected prior to treatment as therapy may decrease the amount of PBG and ALA excreted.

 

Specimens should be frozen immediately following collection and protected from light. PBG is susceptible to degradation at high temperatures, at a pH of less than 5.0, and on prolonged exposure to light.

Clinical Reference Recommendations for 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. Sardh E, Harper P, Andersson D, Floderus: Plasma porphobilinogen as a sensitive biomarker to monitor the clinical and therapeutic course of acute intermittent porphyria attacks. Eur J Intern Med 2009 Mar;20(2):201-207

3. Floderus Y, Sardh E, Moller C, et al: Variations in porphobilinogen and 5-aminolevulinic acid concentrations in plasma and urine from asymptomatic carriers of acute intermittent porphyria gene with increased porphyrin precursor excretion. Clin Chem 2006 Apr;52(4):701-707

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, PA, WB Saunders Company, 2001, pp 584-607

5. Anderson KE, Sassa S, Bishop DF, Desnick RJ: Disorders of Heme Biosynthesis: X-Linked Sideroblastic Anemia and the Porphyrias. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al: New York, NY, McGraw-Hill, 2014. Accessed July 13, 2015. Available at ommbid.mhmedical.com/content.aspx?bookid=971&Sectionid=62638866

Special Instructions Library of PDFs including pertinent information and forms related to the test