Porphobilinogen (PBG), Quantitative, 24-Hour Urine
•PBG, Quantitative, 24-Hour Urine
•Quantitative Porphobilinogen, 24-Hour Urine
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.
Acute attacks of acute intermittent porphyria are precipitated by drugs, including barbiturates, hydantoins, hormones, infection, and diet. The most common symptom of acute intermittent porphyria is abdominal pain. The most common sign is tachycardia.1 Subjects with the porphyrias may pass urine the color of port wine. The term porphyria derives from the Greek “porphyria,” an expression for the color purple.1 Quantitative porphobilinogen will pick up many but not all patients with acute intermittent porphyria in the latent period.
Urine (24-hour), frozen and protected from light
3 mL aliquot
1 mL aliquot
Plastic 24-hour urine container with 30 mL of 30% glacial acetic acid and amber plastic frozen transport tube and cap.
Instruct the patient to void at 8 AM (or 8 PM) and discard the specimen. Then collect all the urine, including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM [or 8 PM] the following day), in the 24-hour collection container. 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 into an 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.) To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Freeze immediately and protect from light. Urine is stable when preserved with 30% glacial acetic acid and frozen for one month or refrigerated for 24 hours.
Specimen not refrigerated during collection; specimen not protected from light; specimen not a 24-hour collection; specimen not frozen.