Porphyrins

This is a test to help diagnose and sometimes to monitor porphyrias (a group of inherited disorders involving disturbance in the metabolism of heme, a component of hemoglobin). Hemoglobin is the red part of your blood that carries oxygen. This test is sometimes done when there are symptoms that suggest an acute neurologic/psychiatric porphyria (such as abdominal pain, tingling in hands or feet, and/or confusion or hallucinations) or a cutaneous porphyria (such as reddening, blistering, or scarring on sun-exposed skin).

Porphyrin tests are assays that are used to help diagnose, and monitor a group of disorders called porphyrias. Most porphyrin tests detect and measure the by-products of heme synthesis. Heme is a part of hemoglobin (the protein inside red blood cells that allows them to transport oxygen) and a number of other proteins.

Porphyrias may be classified according to (1) the affected enzyme, (2) the part of the body where the excess porphyrins are produced (hepatic - associated with the liver or erythropoietic - associated with red blood cell production), or (3) the signs and symptoms of the disease (neurological/psychiatric, cutaneous, or both). Those porphyrias that cause neurological/psychiatric symptoms present with acute attacks that may last for days or weeks. They are associated with abdominal pain, nausea, constipation, depression, confusion, hallucinations, and seizures. Attacks may be triggered by a variety of drugs (such as anticonvulsants, antibiotics, and hormones) and environmental factors (such as dietary changes, stress, and exposure to toxic substances). The cutaneous porphyrias are associated with photosensitivity. Sunlight exposure, even through a glass window, has a toxic effect on the patient's skin. This may cause redness, swelling, and a burning sensation in some patients, while in others it leads to blistering, skin thickening, hyperpigmentation, and in some cases scarring.

ACUTE ATTACK PORPHYRIAS (NEUROLOGICAL/PSYCHIATRIC) INCLUDE:

  • Acute intermittent porphyria (AIP), the most common of the neurological porphyrias.

  • Variegate porphyria (VP), which includes both neurological symptoms and photosensitivity.

  • Hereditary coproporphyria (HCP), which may present with neurological symptoms, photosensitivity, or both.

CUTANEOUS PORPHYRIAS INCLUDE:

  • Porphyria cutanea tarda (PCT), the most common porphyria; unlike the other porphyrias, most cases are due to an acquired enzyme deficiency which is triggered by liver dysfunction.

  • Protoporphyria (also called erythropoietic protoporphyria), which typically begins in childhood or adolescence; sun-exposed skin turns red accompanied by burning and itching, but scarring is uncommon.

  • Congenital erythropoietic porphyria (CEP), a very rare autosomal recessive disorder; over time, extreme photosensitivity leads to extensive and severe scarring of light-exposed areas.

  • In rare cases, a patient may have two different porphyrias, or a homozygous deficiency of one enzyme that produces a more severe form of porphyria.

LABORATORIES MEASURE PORPHYRINS AND THEIR PRECURSORS IN URINE, BLOOD, AND FECES. THESE TESTS ARE LISTED BELOW:

  • Delta-aminolevulinic acid (ALA) in urine.

  • Porphobilinogen (PBG) in urine.

  • Porphyrins in urine, feces, or blood.

  • Zinc protoporphyrin (or free erythrocyte protoporphyrin) in red blood cells.

  • Specialized laboratories may offer testing for one or more of the affected enzymes. The most commonly measured enzyme is porphobilinogen deaminase (PBG-D) in red blood cells, which tests for patients with acute intermittent porphyria. A few research laboratories offer genetic testing for specific gene mutations that cause one of the porphyrias, but this remains primarily a research tool.

SAMPLE COLLECTION

  • The sample collected depends on the porphyrin tests being ordered. It may be one or more of the following:

  • A blood sample obtained by inserting a needle into a vein in the arm

  • A random or 24-hour urine collection (urine must be protected from light during collection).

  • A fresh stool sample that is not contaminated with urine or water.

NORMAL FINDINGS

Total porphyrins (mcg/24 hr):

  • Male: 8-149

  • Female: 3-78

Uroporphyrin (mcg/24 hr):

  • Male: 4-46

  • Female: 3-22

Coproporphyrin (mcg/24 hr):

  • Male: Less than 96

  • Female: Less than 60

Porphobilinogens: 0-2 mg/24 hr or 0-8.8 micromole/day (SI units)

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.