1. Urinary porphobilinogen (PBG) is increased in patients in acute attacks of hepatic porphyrias (AIP, HC, and VP) but not lead poisoning, PCT, CEP or EPP.
2. Assessment of treatment of patients with acute porphyria
1. A normal PBG excretion in a patient with acute symptoms excludes acute porphyria as a cause of the symptoms.
2. Acute porphyria is extremely rare before puberty.
A fresh random urine specimen (preferably in a universal container) without preservative is required. Early morning specimens are preferred although a random specimen is acceptable if the creatinine is greater than 2mmol/L. 24hr collections are not recommended. Urine PBG levels decrease rapidly on exposure to light (the half life is 24hrs). There is no advantage in 24hr collections and some disadvantage including exposure to light, incomplete collections and bacterial growth.
The minimum volume required for assay is 1.5ml – allowing PBG quantitation and creatinine measurement. Paediatric investigations should be discussed with the laboratory.
Dispatch samples by first class post in a container that conforms to Post Office regulations, protected from light, to arrive in the laboratory with 24-48 hours of sampling. When a delay in dispatch is anticipated, due to weekend or bank holiday, samples should be stored frozen and protected from light.
Routine requests are assayed within 5 working days after receipt of sample. Urgent requests should be discussed with the laboratory and dispatched via a courier service. Results can be telephoned or faxed as soon as they become available.
Urine porphobilinogen: creatinine ratio = <1.5 umol/mmol creatinine
< 9.0 umol/24hrs (King’s)
Frontline tests for the investigation of suspected porphyria. A. C. Deacon & G. H. Elder. J. Clin. Pathol. 2001; 54:500-507