Porphobilinogen levels in the urine should be measured during acute attacks of abdominal pain, extremity pain or paresthesias, tachycardia, nausea and vomiting, neurologic abnormalities, and to investigate dark urine. It is an initial test for acute intermittent porphyria, which is characterized by urinary excretion of porphobilinogen and δ-aminolevulinic acid during acute attacks. Increased urinary excretion of porphobilinogen may be caused also by acute attacks of variegate porphyria or of hereditary coproporphyria, and also in lead poisoning (rarely). In lead poisoning, urinary δ-aminolevulinic acid measurement is more useful.
Instruct the patient to collect a 24 hr urine specimen. Specimen must be kept refrigerated during collection. Measure and record on the test request form the 24-hour total volume. Mix well. Transfer the urine aliquot into a LabCorp amber plastic frozen transport tube with amber cap . Label the container with the patient's name, date, and time collection started and finished. The specimen should be frozen immediately and maintained frozen until tested. (If amber tube and cap are not available, cover a clear plastic transport tube completely from top to bottom with aluminum foil. Identify the specimen with the patient's name directly on the transport tube and the outside of the aluminum foil. Secure with tape.)