Porphobilinogen (PBG) is one of several types of porphyrins found in your body. Normally, your body breaks down porphyrins into heme, an important part of hemoglobin. Porphyrins usually leave your body through urine or stools. If this process is interrupted, porphyrins such as PBG can build up in your body.
This article describes the test to measure the amount of PBG in a urine sample.
How the test is performed
A 24-hour urine sample is needed. The health care provider will instruct you, if necessary, to stop taking drugs that may interfere with the test.
On day 1, urinate into the toilet when you get up in the morning.
Afterwards, collect all urine in a special container for the next 24 hours.
On day 2, urinate into the container when you get up in the morning.
Cap the container. Keep it in the refrigerator or a cool place during the collection period.
Label the container with your name, the date, the time of completion, and return it as instructed.
For an infant, thoroughly wash the area around the urethra. Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on the infant. For males, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia. Diaper as usual over the secured bag.
This procedure may take a couple of attempts -- lively infants can displace the bag, causing the specimen to be absorbed by the diaper. The infant should be checked frequently and the bag changed after the infant has urinated into the bag. The urine is drained into the container for transport to the laboratory.
Deliver it to the laboratory or your health care provider as soon as possible upon completion.
How to prepare for the test
Your doctor may tell you to stop taking certain drugs that may interfere with test results.
Drugs that can affect test results include:
Birth control pills
Never stop taking any medicine without first talking to your doctor.
How the test will feel
This test involves only normal urination, and there is no discomfort.
Why the test is performed
This test may be performed when porphyria or another disorder associated with an abnormal porphobilinogen (PBG) level is suspected.
For a random urine sample, a negative test result is considered normal.
If the test is done on a 24-hour urine sample, the normal value is less than 4 milligrams per 24 hours.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What abnormal results mean
Increased levels of PBG in the urine may be due to:
Anderson KE. The porphyrias. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 229.
Wiley JS, Moore MR. Heme biosynthesis and its disorders: porphyrias and sideroblastic anemias. In: Hoffman R, Benz EJ Jr., Shattil SJ, et al, eds. Hoffman Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingstone Elsevier; 2008:chap 38.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.