The porphyrias are inherited or acquired disorders of certain enzymes in the haem biosynthetic pathway that is responsible for the synthesis of haemoglobin, myoglobin and cytochrome. They are broadly classified as hepatic porphyrias or erythropoietic porphyrias, based on the site of their overproduction and subsequent accumulation (or their chemical precursors).
An acute attack of porphyria almost invariably starts with continuous, severe abdominal pain, with autonomic neuropathy developing in two thirds of patients. Acute attacks of porphyria are usually associated with raised urinary excretion of PBG (and δ-aminolaevulinic acid). Consequently, a raised level is seen in acute intermittent porphyria, hereditary coproporphyria and variegate porphyria. A random urine specimen associated with a symptomatic episode is required because between attacks, concentrations of PBG are often normal.
Random urine protected from light
The in-house method is adequate only for the investigation of symptomatic patients but is unsuitable for family studies, measurements during remission or for making retrospective diagnosis.