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Urinalysis
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Currently under review
Pending specialist review and validation.
This test measures the amount of porphobilinogen (PBG) your body releases into urine over a full 24-hour period. PBG is a natural intermediate in the pathway that makes heme, the oxygen-carrying component of hemoglobin and many enzymes. When certain enzymes in this pathway are not working properly, PBG can build up and spill into the urine.
A timed 24-hour collection helps capture day-to-day variation and peaks that may occur during symptoms. The laboratory may ask you to keep the container cool or use a preservative so the sample stays stable from the first to the last collection.
Doctors order this test when symptoms suggest an acute hepatic porphyria, such as severe abdominal pain, nausea, constipation, dark urine, muscle weakness, tingling, or changes in mood or thinking. PBG often rises quickly during an attack, so measuring it in a 24-hour urine sample can help confirm the diagnosis and guide urgent treatment.
Results can also help monitor response to therapies and inform longer term care, including avoidance of known triggers and consideration of genetic testing. Related tests, such as urinary delta-aminolevulinic acid (ALA), urine porphyrins, and plasma studies, are often used together to give a complete picture.
Your clinician will interpret this result alongside your symptoms and other tests. A higher than expected PBG in urine supports a diagnosis of an acute hepatic porphyria in the right clinical context. If your result is within the expected range during symptoms, an acute attack becomes less likely, although timing matters and repeat testing during or soon after symptoms may be recommended.
If results are borderline or unclear, the laboratory may repeat testing or use a more specific method. Your care team may also review medications and other triggers, order companion tests such as ALA and urine porphyrins, and discuss genetic evaluation. Seek urgent care if you develop severe or worsening symptoms, regardless of pending test results.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Missing any urine during the 24-hour window, recording the wrong start or stop time, or spilling the sample can lead to inaccurate results. Follow the instructions, discard the first void at start time, collect all urine thereafter, and include the final void at the 24-hour mark.
PBG tends to be highest during an acute attack and may fall between episodes. Collecting as early as possible during or right after symptoms increases the chance of detecting an abnormal rise.
Improper storage can degrade analytes. Use any provided preservative, keep the container capped, and refrigerate the collection if instructed. Avoid heat and prolonged light exposure to maintain sample stability.
Certain drugs and exposures can precipitate attacks or alter PBG, including some barbiturates, anti-seizure medicines, rifampin, sulfonamides, alcohol, and fasting. Treatments like hemin and givosiran can lower PBG. Share your medication list with your clinician.
Reduced kidney function and extreme dehydration can change how substances are cleared into urine, which may affect measured excretion over 24 hours. Your clinician will consider renal status and clinical context when interpreting results.
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