Testing for Porphyria
Official guidelines for the Porphyria Association Inc. by Professor Edward Janus and Virginia Cronin
Last update: February 2022
There are two ways to test for acute and cutaneous porphyria: biochemical testing and genetic testing.
When to Test
Test as soon as possible; test at first suspicion and then test again when the symptoms or an attack are at their worst. Testing between attacks can be useful to help understand an individual's biochemical profile and to help screen family members. It is better to test as soon as possible rather than to delay testing, waiting for worsening symptoms or an acute attack. Testing can then be repeated at another time.
False negative results are possible and often happen when samples are not handled correctly.
Once there is a clear diagnosis, further testing is not usually required but may be helpful during acute attacks, periods of worsening symptoms or if new treatments are being tried.
Bio-chemical Testing (Urine, Faeces and Blood samples)
Any doctor can request “porphyrin studies” or a “porphyrin screen"
It is best to write "porphyrin screen" under the request for faeces, urine and blood samples on the request section of a pathology form
In the clinical information section, write “? porphyria attack” or “? latent familial porphyria” or “symptoms: skin rash/skin lesions/abdominal pain” or a short case history
Also note on the form "please send samples to porphyrin reference lab with light protection"
Urine: 200ml aliquot from 24hr urine collection OR spot sample of at least 100ml (preferably first morning, midstream), WRAP IN FOIL
Faeces: apricot size sample in sealed container, WRAP IN FOIL
Blood: 10ml whole blood in lithium heparin container (green topped tube), WRAP IN FOIL
For most patients, the main abnormalities are found in the faeces and urine so always send these specimens
Blood samples can identify some unusual or rare forms of porphyria so can be useful to send but might be less critical
Porphyrins are destroyed by light so all samples need to be protected from the light by wrapping them in aluminium foil
IMPORTANT LIGHT WILL BREAK DOWN PORPHYRINS AND MAY GIVE AN INVALID TEST RESULT
Light protect all samples; wrap them carefully in aluminium foil or a black garbage bag
Label the sample with your name, date and time of collection on the outside of the aluminium foil or garbage bag
Keep the samples cool
Send samples to your nearest Porphyrin Laboratory (listed below), quicker is better (preferably within a day)
These tests are performed in Melbourne by the Royal Melbourne Hospital and in Sydney by the Royal Prince Alfred Hospital. Other laboratories will forward the samples to these reference centres.
Genetic testing can be done once there is a clear biochemical diagnosis from the above tests.
Important information for Australians:
The following is a statement from the Royal Prince Alfred Hospital (RPA), Sydney genetics team: "a "known diagnosis” in usual practice would mean someone in the family with a biochemically confirmed test result for any inherited porphyria, another point is that identifying the mutation in the first family member can take months."
Genetic testing is available for individuals with a known diagnosis of an inherited porphyria and their blood relatives. Genetic testing is performed in a stepwise process; firstly on an affected individual and then if a gene mutation is identified (97% of the time) genetic testing can be offered to relatives who may be at risk of having the mutation. Extended blood relatives may be able to find out whether they have inherited porphyria and take appropriate preventative measures. Although only about one third of people with porphyria will develop symptoms of the condition, they could still pass it on to their children who may or may not suffer from symptoms. There is a clear clinical benefit in knowing whether you have inherited porphyria or not as practices to avoid triggers can be used.
Genetic testing can be done through genetic clinics, which operate in most states of Australia and internationally. A list of Australian Genetic Clinics is available here.
To see a geneticist you will require a referral letter from your General Practitioner or Porphyria Specialist.
To see an in-depth discussion on testing see the video below:
NOTE : If you or your patient receives a positive test please see a list of referral centres within Australia / New Zealand