Porphobilinogen, Quantitative, Random, Urine
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Urinary porphobilinogen (PBG) is elevated during the acute phase of the neurologic porphyrias: acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). Acute attacks may produce symptoms of cerebral dysfunction and damage (confusion, "psychiatric disease"), autonomic neuropathy, constipation, urinary retention, tachycardia, hypertension, and severe (sometimes chronic) abdominal pain. In the acute phase, these disorders can be life threatening. Between attacks patients have mild symptoms that may include psychoneuroses. Several studies indicate that approximately 1 in 300 psychiatric patients have AIP.
The common symptoms of AIP, HCP, and VP mimic many other diseases from acute appendicitis to acute schizophrenia. Acute episodes usually begin with or include abdominal discomfort ranging from mild cramping to severe pain that suggests a need for surgical intervention. These symptoms and outward signs are common to a variety of medical problems and diagnosis usually depends on timely, accurate laboratory testing. Frequently, surgical intervention can be avoided if the laboratory returns an elevated level for urinary PBG. For additional information on the recommended order of testing, see Porphyria (Acute) Testing Algorithm and Porphyria (Cutaneous) Testing Algorithm in Special Instructions. Refer to The Challenges of Testing For and Diagnosing Porphyrias, Mayo Medical Laboratories Communique 2002 Nov;27(11) for more information regarding diagnostic strategy.
First-line test for establishing a tentative diagnosis for acute neuropathic porphyria including acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria.
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 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
Ideally, specimen collection should occur during the acute phase. Porphobilinogen (PBG) may be normal when the patient is not exhibiting symptoms.
PBG is susceptible to degradation at high temperatures, at pH <5.0, and on prolonged exposure to light. Specimens should be frozen immediately following collection and protected from light.
Urine and fecal porphyrin analysis should be performed to confirm the diagnosis and to distinguish between acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). A biochemical diagnosis of AIP can be confirmed by measurement of PBG deaminase activity (PBGD_/88925 Porphobilinogen [PBG] Deaminase, Whole Blood). VP and HCP can be confirmed by measurement of fecal porphyrins (FQPPS/81652 Porphyrins, Feces).
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.
< or =1.3 mcmol/L
Clinical References 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 BookCompany, 2001, pp 2991-3062