Examination of urine for excess porphobilinogen (measurement of 5-aminolaevulinic acid is not essential to establish the diagnosis). Elevated porphobilinogen levels in urine (or plasma) are specific for acute porphyria. The test can be performed in a random sample with the result normalized per gram of urine creatinine; a 24-hour collection is not required.
Urinary porphobilinogen and 5-aminolaevulinic acid are increased in all three acute hepatic porphyrias (acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria) although the concentrations are higher and longer lasting in acute intermittent porphyria than in the other two types (hereditary coporphyria and variegate porphyria).
With a recorded porphobilinogen over excretion (>10 times the upper limit), treatment can be started immediately, with further laboratory investigations used to define the porphyria type in the proband.
For diagnosis of the type of acute porphyria in the proband, plasma fluorescence emission spectroscopy is a fi rst-line test because a peak at 624–628 nm establishes the diagnosis of variegate porphyria.
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