Porphobilinogen (PBG) is one of several types of porphyrins found in your body. Porphyrins help form many important substances in the body. One of these is hemoglobin, the protein in red blood cells that carries oxygen in the blood. Porphyrins usually leave your body through urine or stools. If this process does not occur, 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
After you provide a urine sample, it is tested in the lab. This is called a random urine sample.
If needed, your health care provider may ask you to collect your urine at home over 24 hours. This is called a 24-hour urine sample. Your provider will tell you how to do this. Follow instructions exactly so that the results are accurate.
How to Prepare for the Test
Your provider may tell you to temporarily stop taking medicines that may affect the test results. Be sure to tell your provider about all the medicines you take. These include:
Antibiotics and anti-fungal drugs
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 done if your provider suspects porphyria or another disorder associated with an abnormal PBG level.
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.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
An increased level of PBG in the urine may be due to:
Fuller SJ, Wiley JS. Heme biosynthesis and its disorders. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, Anastasi J, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 36.
McPherson RA, Ben-Ezra J. Basic examination of urine. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 28.
Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.