Porphyrins

Porphyrias are a group of rare conditions, which either affect the skin or nerves, or both. Porphyrin tests are used to diagnose and monitor porphyrias. Most of the porphyrin tests are used to detect and measure products which are produced during the synthesis of haem, which is a component part of haemoglobin. The production of haem involves eight major enzymes; if the patient has a deficiency of one of these enzymes, there will be a back-up and precursors will collect in the fluid and tissues in the body.

There are six main porphyrias, which are caused by a deficiency of a particular enzyme. Porphyrias are categorised according to the enzyme deficiency, the location of the back-up and subsequent pre-cursor collection and the signs and symptoms produced by the disease.

When is the test used?

The test is used as a diagnostic tool when a doctor suspects that a patient may have porphyrias; the symptoms are often similar to those associated with many other health conditions so the test can be used to reach a diagnosis.

The test is also helpful for people who have already been diagnosed with porphyrias, as it allows doctors to monitor their condition.

A urine test will usually be ordered when a patient has symptoms of acute porphyria, including vomiting, abdominal pain, constipation, tingling in the hands and feet and muscle weakness.

A blood test may be ordered when a patient has symptoms including blisters, skin lesions, redness and scarring.

How is the test done?

The test is done by taking a sample of blood from the patient’s arm (usually from a vein on the inside of the elbow); a needle is inserted into the vein and the blood is drawn out using a syringe. The blood collects in the syringe and is transferred to a sample bottle; once the doctor or nurse has a sufficient sample, the bottles will be labelled and sent away to the laboratory for analysis.

Sometimes a urine sample or a stool sample may be collected.

What do the test results show?

The results of the porphyrin test may be affected by many other health conditions, so it is important that they are interpreted in the context of the individual patient.

Different porphyria are categorised by different test results, as follows:

  • Acute porphyria: increased ALA (delta-aminolaevulinic acid) and PBG (porphobilinogen), increased URO (uroporphyrins), normal faecal porphyrins, normal red blood cell porphyrins.
  • Variegate porphyria: increased ALA and PBG, increased COPRO (coproporphyrins), increased PROTO (protoporphyrins), normal red blood cell porphyrins.
  • Hereditary coproporphyria: increased ALA and PBG, increased COPRO, increased COPRO, normal red blood porphyrins.
  • Porphyria curtanea tarda: normal ALA and PBG, increased URO and 7-carboxyl, increased isocoproporphyrin, normal red blood cell porphyrins.
  • Protoporphyria: normal ALA and PBG, normal urine porphyrins, increased PROTO and increased PROTO in the red blood cells (zinc protoporhyin)
  • Congenital erythopoietic porphyria: normal ALA and PBG, increased URO and COPRO, increased COPRO (in the faeces), increased COPRO (in the red blood cells).

Specific Blood Tests

Blood Test Guide

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