At a glance
Also known as
Uroporphyrin, Coproporphyrin, Protoporphyrin, Delta-aminolevulinic Acid, ALA, Porphobilinogen, PBG, Free Erthrocyte Protoporphyrin, FEP
Why get tested?
To help diagnose and sometimes to monitor porphyrias (a group of inherited disorders involving disturbance in the metabolism of haem, a part of haemoglobin)
When to get tested?
If a patient has 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 of sun-exposed skin)
A blood sample drawn from a vein in your arm, a urine sample, preferably collected whilst symptoms are occurring, and a small stool sample
Test preparation needed?
What is being tested?
Porphyrins are a group of compounds defined by their chemical structure. These compounds are by-products of haem synthesis and are normally present at low concentrations in blood and other body fluids. Porphyrin tests measure porphyrins and their precursors in urine, blood, and/or stool.
Haem is an iron-containing pigment that is a part of haemoglobin and a number of their proteins. It consists of an organic portion (protoporphyrin) bound to an iron atom. The synthesis of haem is a step-by-step process that requires the action of eight different enzymes. If there is a deficiency in one of these enzymes, the process is disrupted and intermediate porphyrins such as uroporphyrin, coproporphyrin, and protoporphyrin build up in the body's fluid and tissues. The precursors that accumulate depend on which enzyme is deficient, and they can exert toxic effects on the body.
Porphyrin tests are assays that are used to help diagnose, and sometimes monitor a group of disorders called porphyrias.
There are seven major porphyrias, and each one is associated with a different enzyme deficiency. Most porphyrias are inherited, resulting from a gene mutation usually in an autosomal fashion, with one normal and one affected gene. This results in about a 50% reduction in the activity of the haem-related enzyme. Enough haem is synthesised to prevent the affected person from becoming anaemic, but a large excess of one or more precursors is produced.
Porphyrias may be classified according to the:
- affected enzyme
- part of the body where the excess porphyrins are produced (hepatic - associated with the liver or erythropoietic - associated with red blood cell production), or
- and 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
- Delta-aminolevulinic Acid (ALA) dehydratase porphyria (ADP), which is very rare (less than 10 cases worldwide to date)
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 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.
Clinical laboratories measure porphyrins and their precursors in urine, blood, and faeces. These tests are listed below:
- Delta-aminolaevulinic acid (ALA) in urine
- Porphobilinogen (PBG) in urine
- Porphyrins in urine, faeces or blood
Specialised 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. Genetic testing for specific gene that cause porphyrias, is becoming more common and replacing measurement of the affected enzymes in many cases.
How is the sample collected for testing?
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 (urine must be protected from light during collection)
- A fresh stool sample that is not contaminated with urine or water
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.