Porphobilinogen (PBG) in Urine: Acute Porphyria

Clinical Chemistry

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Description

The porphyrias are a group of disorders of haem biosynthesis in each of which there is an inborn defect affecting a specific enzyme. As a result of this haem precursors accumulate and may result in clinical manifestations. The majority of porphyrias are autosomal dominant with low penetrance. Abnormal porphyrin metabolism may also be secondary to other disease. PBG excretion is increased in acute porphyrias. Slight increase in PBG excretion may be seen in liver disease and occasionally with hepatocellular carcinoma. PBG excretion decreases as the attack resolves. In AIP, excretion usually remains increased for many weeks but in VP and HCP may return to normal or near normal within a week or so after the onset of symptoms. If a urine PBG test is positive, detailed investigation would be required on blood, urine and stool specimens forwarded to Cardiff.

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Indications

Acute porphyria: Porphobilinogen ( PBG ) is used to exclude acute porphyria as a cause of acute neuro-visceral symptoms such as abdominal pain, peripheral neuropathy, muscle weakness, confusion and hallucinations. In suspected acute porphyria it is important to collect urine during an acute attack since the biochemistry may be normal between attacks. Also used in monitoring acute porphyria patients when indicated.

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Sample Type

PROTECT SAMPLES FROM LIGHT. Urine, plain bottle, random but early morning preferred 20mL

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Reference Range

Reference ranges are provided on the report. Alternatively, please contact the laboratory for current ranges.

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Turnaround Time

Within 1 week

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Testing Frequency

Weekly ( Fridays, except Bank Holiday Fridays )

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External Notes

A fresh urine specimen obtained when symptomatic may be all that is required to exclude acute porphyria. Concentration of urine has a major effect on results - hence the need to calculate ratio of porphyrin precursors to creatinine.

Send within 24hr or store in the fridge for up to 3 days protected from light. Avoid freezing if possible, especially repeated freeze-thaw cycles, as this can lead to a marked decrease in PBG.  

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Patient Preparation

Early morning samples are preferred to avoid dilute urine

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.