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Ency. home > Test > P > PBG

PBG   

Overview | Risks | Results

Alternative names:

PHB; Porphobilinogen

Definition:

A test that measures the amount of PBG in urine.

How the Test is Performed

A 24 hour urine sample is needed.
The health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.

  • On day 1, urinate into the toilet upon arising in the morning.
  • Collect all subsequent urine (in a special container) for the next 24 hours.
  • On day 2, urinate into the container in the morning upon arising.
  • 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.
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 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. 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, causing an inability to obtain the specimen. 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

No 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 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.

PBG is a substance (enzyme) used by the body to make important substances such as the molecule call heme. Heme is a complex molecule that incorporates iron. The heme molecule is the oxygen carrying part of Hemoglobin found in red blood cells.

Various kinds of porphyrins exist with the same basic structure, but with slightly different chemical appearance. The major biochemical pathway includes several enzymatic conversions from the starting porphyrin molecule through several intermediates (delta-ALA, PBG, uroporphyrin, coproporphyrin, and protoporphyrin) to finally yield the end product, heme.

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), a type of porphyria results.

Ency. home > Test > P > PBG

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