What is the role of urine and stool studies in the workup of porphyria?

Updated: Aug 31, 2020
  • Author: Brenda Chiang, DO; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

Answer

Urine and stool studies in various types of porphyria are summarized in the image below.

Porphyrins in stool and urine in different porphyrias.

Urine

Urine porphyrin studies are the mainstay in the diagnosis of acute porphyria attacks. Establish the diagnosis promptly by testing for increased porphobilinogen (PBG) in a single-void urine collected during an attack. An expert guidelines panel recommended the Trace PBG Kit [Thermo Trace/DMA, Arlington, Tex]. [33]  

Urine samples for PBG testing should be protected from light (eg, by wrapping the specimen container in aluminum foil or placing it in a brown paper bag). However, brief exposure to light will not compromise the test results. Urine study results are unreliable if the urine creatinine level is below 2 mmol/L. [52]

 Patients with acute exacerbations of porphyria have logarithmic increases (5-100 times) in metabolic precursors (eg, aminolevulinic acid [ALA], PBG). Minor elevations of these precursors are nondiagnostic and nonspecific. [53]

Significantly increased ALA and PBG in urine have 100% specificity (ie, rules in) for acute intermittent (hepatic) porphyria, variegate porphyria, and coproporphyria. A normal urine PBG result has a sensitivity of almost 100% (ie, rules out) in the diagnosis of porphyria in acutely symptomatic patients. [54]


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