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Porphyrins

Formal name: [Primary tests]; Delta-aminolaevulinic acid (ALA); porphobilinogen (PBG); porphyrins

The Test

How is it used?

Porphyrin testing is used to help diagnose and sometimes to monitor porphyrias. Since the symptoms associated with these disorders may also be seen in a variety of other conditions, testing is also used to help rule out the presence of a porphyria in someone who presents with neurologic/psychiatric or skin symptoms.  

For acute attacks, porphobilinogen (PBG) and, rarely, delta-aminolaevulinic acid (ALA), may be requested on a random urine sample. The urine should be collected whilst symptoms are occurring as levels may only be abnormal at this time and should be protected from light. Where positive, faecal porphyrins may be requested to help distinguish between VP and HCP. 

For cutaneous (skin) porphyrias, whole blood, plasma and urine porphyrins are the most frequently requested tests. They are used to help diagnose a porphyria, and may be used to monitor treatment.

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When is it requested?

PBG may be requested on a random urine specimen when a patient has symptoms that suggest an acute porphyria, such as abdominal pain, sickness, constipation, peripheral neuropathy (tingling, numbness, or pain in the hands and feet), muscle weakness, urinary retention (not passing urine normally), confusion, and hallucinations. Where positive, faecal porphyrin testing may be requested to help distinguish between porphyrias.

Depending upon the patient’s age and symptoms, a test for urine and blood porphyrins should be requested when a patient presents with blisters, scarring, redness, or other skin lesions in sun-exposed areas.

Enzyme testing may be requested to confirm the diagnosis of porphyria and to identify family members of a known patient who may have inherited the disease but have not yet developed signs or symptoms.

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What does the test result mean?

Looking for reference ranges?

Care must be taken when interpreting porphyrin test results. Some porphyrins or their precursors may be mildly to moderately elevated in patients with other diseases or conditions. In addition, levels of ALA, PBG and porphyrins may fall to near normal levels between acute attacks of a neurologic porphyria. While negative test results mean that it is unlikely that a patient’s symptoms are caused by a porphyria, positive initial tests should be confirmed with follow-up testing.  

PBG is significantly increased in most patients with an acute porphyria. ALA is less specific than PBG, as it may be elevated in other conditions as well. Specific porphyrins are elevated in each of the porphyrias, and the pattern of elevation (which porphyrin is elevated in which sample) determines the diagnosis. Urine, blood, and stool porphyrins may be increased up to several-fold in a variety of other conditions. Interpretation of the patterns can be difficult, and this should be done by a physician or laboratory scientist with expertise in the area.

An abnormal enzyme test or the detection of a gene mutation indicates that a family member has inherited a porphyria. However, enzyme and gene tests cannot determine whether that individual will develop signs and symptoms of porphyria or, if they do, how severe it is likely to be. Fortunately, the majority of gene carriers never have an attack.

Results seen with specific porphyrias include:

Type of Porphyria
 Urine ALA and PBG* Urine porphyrins Fecal porphyrins Red Blood Cell Porphyrins
Acute intermittent porphyria
Increased Increased URO* Normal Normal
Variegate porphyria Increased Increased COPRO Increased PROTO, COPRO Normal
Hereditary coproporphyria
 Increased Increased COPRO Increased COPRO Normal
Porphyria curtanea tarda Normal Increased URO, 7-carboxyl Increased Isocoproporphyrin Normal
Protoporphyria
 Normal Normal Increased PROTO Increased PROTO (zinc protoporhyrin)
Congenital erythropoietic porphyria Normal
 Increased URO, COPRO Increased COPRO Increased COPRO
URO = Uroporphyrins; COPRO = Coproporphyrins; PROTO = Protoporphyrins
* May be increased only during acute attack

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Is there anything else I should know?

A variety of drugs, alcohol, and other environmental factors such as diets, stress, and illness, can trigger acute attacks of a neurologic porphyria in those with latent or inactive disease. Click here for a safe list of drugs for those with Acute Porphyria.  

Women are more susceptible due to a triggering effect of female hormones, particularly progesterone and attacks may be linked to the menstrual cycle. Oral contraceptive and HRT preparations containing progesterone or related compounds (progestogens) should be avoided, if at all possible, by women with an acute porphyria. 

By the same token, sun exposure will induce skin lesions in patients with a skin porphyria. Lifestyle modification to avoid aggravating factors is the most effective way to minimise the impact of a porphyria.

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