Testing porphyrins to diagnose porphyria
Porphyrins are natural chemicals that are found in your body. They are an important part of many of your body’s functions.
Usually, your body makes a small amount of porphyrins when it produces heme. Heme is an important component of hemoglobin, the protein in red blood cells that carries oxygen. Heme production involves a multistep process, and a different enzyme controls each step. If one of these enzymes is defective, this can cause porphyrins to build up in your body and potentially reach toxic levels. This causes the clinical disease porphyria.
Porphyria is rare. Most types of porphyria are passed to a person through their genes. If your doctor suspects that you have a type of porphyria, they will want to do some tests to establish the level of porphyrins in your body. One way to test this is through urine testing.
One type of porphyrin urine testing is with a random, single urine sample, or they may ask you to complete a urine test over a 24-hour period. The production and elimination of porphyrins may vary throughout the day and between attacks, so a random sample may miss elevated porphyrin levels. A 24-hour urine test is painless and just requires a simple urine collection done in three stages.
Types of porphyria diagnosed with a porphyrins urine test
Porphyrias can be grouped into two main types, neurologic porphyrias and cutaneous porphyrias.
Neurologic porphyrias affect your nervous system. They’re also known as acute porphyrias because they show up suddenly and cause severe symptoms for a short time.
Cutaneous porphyrias result in sensitivity to the sun, leading to skin problems like blisters or itching.
Doctors may use porphyrin urine testing as part of their diagnosis of the following types of neurologic porphyrias:
- acute intermittent porphyria
- variegate porphyria
- hereditary coproporphyria
- ALA dehydratase deficiency porphyria
They may also use it if they suspect that you have porphyria cutanea tarda, a type of cutaneous porphyria.
How to prepare for a porphyrins urine test
Parents of infants taking a urine test may wish to have extra collection bags available in case an active baby dislodges the bag.
If you’re an adult taking the test, your doctor may instruct you to stop taking drugs that could interfere with the accuracy of the porphyrins urine test. Be sure to follow your doctor’s guidance and instructions when stopping medications.
The following drugs may interfere with an accurate measurement of porphyrins in your urine:
- aminosalicylic acid, aspirin (Bayer Advanced Aspirin, Bufferin)
- birth control pills
- chloral hydrate
- griseofulvin (Gris-PEG)
- phenazopyridine (Pyridium, Uristat)
24-hour urine test procedure for adults
Here’s how the collection procedure for a 24-hour urine test works:
- On day one, you urinate into a toilet upon rising in the morning. Flush this first sample away.
- For the rest of the day, you collect all of your urine in a special container and store it in a cool place.
- On day two, you urinate into the special container upon rising in the morning.
- After that, you return the container to the lab as soon as possible.
24-hour urine test procedure for babies
If you’re the parent of a baby taking the urine test, you need to follow this procedure:
- On day one, wash the area around your baby’s urethra, then attach a collection bag to that area. For a boy, you place the bag over his penis. For a girl, place the bag over her labia. You can then put your baby’s diaper on over the bag.
- Over the rest of the 24-hour period, collect samples according to the same schedule as adults.
- Throughout the day, check the bag. Change the bag each time your baby urinates.
- Each time your baby urinates, pour the sample into the collection container. Keep this container in a cool place.
- On day two, collect the final sample when your baby first wakes up.
- Return the container to the lab as soon as possible.
What the results mean
The normal range for a 24-hour porphyrins urine test is about 50 to 300 milligrams, although results vary among different laboratories.
Abnormal test results can indicate liver cancer, hepatitis, lead poisoning, or one of the different forms of porphyria. Your doctor will be able to interpret the results for a diagnosis and recommend the best course of treatment.