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Alternative namesPHB; Porphobilinogen
DefinitionThis is a test that measures the amount of PBG in urine.
How the test is performedA 24-hour urine sample is needed. The health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.
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 your infant. For boys, the entire penis can be placed in the bag and the adhesive attached to the skin. For girls, the bag is placed over the labia. Place a diaper over the infant (bag and all).
The infant should be checked frequently and the bag changed after the infant has urinated into the bag. For active infants, this procedure may take a couple of attempts -- lively infants can displace the bag, making it difficult to obtain the specimen. The urine is drained into the container for transport to the laboratory.
How to prepare for the testNo special preparation is necessary for this test, but if the collection is being taken from an infant, a couple of extra collection bags may be necessary.
How the test will feelThis 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.
Each step requires the presence of an enzyme. If any of the enzymes are deficient (because of a genetic disease or inhibition by a toxic substance), porphyria results.
Normal values are as follows:
What abnormal results meanIncreased levels of urinary PBG may indicate:
What the risks areThere are no risks.
Special considerationsDrugs that can affect test measurements include: aminosalicylic acid, barbiturates, chloral hydrate, chlorpropamide, ethyl alcohol, griseofulvin, morphine, oral contraceptives, phenazopyridine, procaine, and sulfonamides.
Update Date: 2/9/2004Frank A. Greco, M.D., Ph.D., Director, Biophysical Laboratory, The Lahey Clinic, Burlington, MA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT