DIAGNOSING PORPHYRIA
All porphyria diagnoses are confirmed by biochemical testing (using urine, blood and/or stool samples). “Clinical diagnoses” without positive biochemical results are not considered diagnostic of porphyria.
First Line Testing
Biochemical testing, or blood and urine tests, are the first ones that should be done when a type of porphyria is suspected. The specific biochemical tests depend on the symptoms. For all the first line tests the results will be very high if someone has porphyria. Small increases in these tests are generally not diagnostic.
Acute attack symptoms (i.e. abdominal pain, nausea, vomiting, other pain, etc.) suggestive of an acute porphyria: a urine porphobilinogen (PBG) test, this is different than a test looking for urine total porphyrins.
Blistering skin symptoms suggestive of PCT, CEP, HEP, VP, or HCP: a blood test called plasma total porphyrins, and a urine total porphyrins test.
Non-blistering skin symptoms suggestive of EPP or XLP: the blood tests plasma total porphyrins and erythrocyte protoporphyrins.
Making Sure Tests are Done Properly
Most of these tests can be done properly at any laboratory. Only erythrocyte protoporphyrin testing should be done at specific labs.
These biochemical tests are sensitive to being in sunlight for extended periods of time, special brown containers are generally used when collecting the samples.
Detailed testing and diagnosis information for your healthcare provider is available here.
Genetic Testing
Each type of porphyria (with exception of Sporadic PCT) is caused by a mutation, or change, in the genetic material that codes for a specific enzyme in the heme pathway. This testing is done on a blood, saliva, or mouth swab sample, generally after the biochemical testing has been done in someone who was recently diagnosed, or in family members of someone with a porphyria.
The different genes that cause the porphyrias are:
ALA-Dehydratase Porphyria (ADP): ALAD
Acute Intermittent Porphyria (AIP): HMBS
Congenital Erythropoietic Porphyria (CEP):UROS
Porphyria Cutanea Tarda (PCT), familial form: UROD
Hepatoerythropoietic Porphyria (HEP): UROD
Hereditary Coproporphyria (HCP): CPOX
Variegate Porphyria (VP): PPOX
A very small number of people who have a biochemical diagnosis of porphyria may not have a gene change found.
Testing Family Members
Recommendations for testing family members depends on how the different porphyrias are inherited.
Autosomal dominant disorders (AIP, VP, HCP & PCT)—testing of first-degree relatives (parents, siblings and children) is recommended once a diagnosis has been confirmed in someone with symptoms to provide appropriate counseling to family members who may also be at risk of developing symptoms.
Recessive disorders (ADP, CEP, EPP, HEP)—testing of relatives can be done for family planning information. Carriers of recessive conditions do not generally have symptoms of the disorder.
X-linked disorders (XLP)—testing of family members depends on the sex of the affected person and their relatives. A female with an X-linked disorder has a 50% chance of passing the disorder to any of her children with each pregnancy. However, a male with an X-linked condition will pass it on to all of his daughters but none of his sons.
For more information on who should be tested in your family talk to a porphyria specialist or genetic counselor.
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