Porphyrins - urine
This is a test that measures the level of porphyrins 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.
Thoroughly wash the area around the urethra. Open a Urine collection bag (a plastic bag with adhesive 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
The health care provider may advise you to discontinue drugs that can affect the test. (See “Special considerations.”)
If the collection is being taken from an infant, a couple of extra collection bags may be necessary.
How the test will feel
The test will feel the same as normal urination.
Why the test is performed
This test is most often performed when porphyria or other disorders that can cause abnormal urine porphyrins is suspected.
The most important function of porphyrins is as components of heme. Heme is made from iron + protoporphyrin. Hemoglobin is made up of four heme molecules + four globin proteins. Oxygen binds to the iron in the heme molecules.
Various kinds of porphyrins exist with the same basic structure, but with slightly different chemical appearance.
Heme production involves biochemical conversion of porphyrins into delta-ALA, then to PBG, then uroporphyrin, then coproporphyrin, then protoporphyrin, and finally into the end product - heme.
Each of these steps requires the presence of a specific enzyme. If any of the enzymes are deficient (because of a genetic disease or interference by a toxic substance), the intermediate substances build up, and a type of porphyria results.
- Random urine: negative test
- 24-hour urine: 50 - 300 mg (milligrams) per 24 hours
What abnormal results mean
Increased levels of urinary PBG may indicate:
- Liver cancer
- Lead poisoning
- Porphyria (several types)
In specific types of porphyria, levels of ALA, uroporphyrin, and coproporphyrin may also be higher than normal.
What the risks are
There are no risks.
Drugs that can affect test measurements include aminosalicylic acid, birth control pills, barbiturates, chloral hydrate, chlorpropamide, ethyl alcohol, griseofulvin, morphine, phenazopyridine, procaine, and sulfonamides.
by David A. Scott, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.