DIAGNOSING PORPHYRIA: PATIENTS WITH SUGGESTIVE SYMPTOMS

NB The diagnostic algorithms recommended in the pages are designed for patients in the South African context. Approaches will differ for patients in other settings.

Rather than relying on a single standard set of diagnostic tests for porphyria, clinicians should tailor the tests they request to the clinical problem for which an answer is required. The following guidelines are based on the typical clinical problems with which the doctor and dealing with porphyria (or possible porphyria) is faced. These guidelines are designed for the diagnosis of South African patients, who have a high incidence of one type of porphyria (variegate porphyria), resulting from a single founder mutation. Our diagnostic algorithms are based on the high probability of this type of porphyria in this population, and also on the diagnostic techniques employed in our laboratory. A modified approach will be necessary for patients in other settings.

THE PATIENT SUSPECTED OF HAVING AN ACUTE ATTACK

In South Africa, the most frequent causes of the acute attack of both variegate porphyria (VP) and acute intermittent porphyria (AIP). It is important to test for both. It is essential to submit both urine and blood and not blood alone, since it is only by testing urine for the presence of ALA and PBG that one can confirm the presence of an acute attack, or even make a diagnosis of AIP.

Step 1: Confirm the presence of an acute attack

A urine sample should be screened for the presence of PBG. Urine must therefore be sent to laboratory with an assist expertise as soon as possible. a screening test for PBG is a simple test which can easily be performed as a side-ward investigation if one has access to the reagent (Ehrlich's aldehyde). The technique is set out in the following page: Simple Screening Test for the Acute Attack.

Step 2: Define the type of porphyria and measure its severity

ALA, PBG and porphyrin concentrations should be measured in urine by chromatographic analysis. If you do not know which type of porphyria the patient has, submit a blood sample (EDTA blood, two mauve-topped haematology tubes) for plasma scanning.

PATIENTS WITH SKIN DISEASE

Submit blood and urine to a laboratory with expertise in the diagnosis of porphyria. Request a plasma porphyrin scan and urine porphyrin quantitation. A plasma fluorescence peak 625 nm is highly suggestive of variegate porphyria; a plasma fluorescence peak at 619 nm with characteristic accumulation of early water-soluble porphyrins in the urine is suggestive of porphyria cutanea tarda.

PATIENTS WITH A HISTORY OF UNEXPLAINED ABDOMINAL PAIN

Submit blood and urine to a laboratory with expertise in the diagnosis of porphyria. A plasma fluorescence peak at 625 nm is highly suggestive of variegate porphyria, but the urine porphyrins(and preferably the ALA and PBG) must be shown to be elevated if abdominal symptoms are to be ascribed to the porphyria. In the case of AIP, urine ALA and PBG are elevated and are accompanied by increased concentrations of porphyrins in the urine and possibly a plasma fluorescence peak at 619 nm.

ASSESSING DISEASE ACTIVITY IN PATIENTS ALREADY PROVEN TO HAVE PORPHYRIA

Acute symptoms (typically abdominal pain) must NOT be ascribed to porphyria unless:

• An acute porphyria (VP, AIP or hereditary coproporphyria) has been unequivocally diagnosed in the patient (N.B. for practical purposes, one cannot be a "latent" case and be symptomatic at the same time!)
  
  
• The porphyria has been shown to be active by demonstrating significantly elevated urine porphyrin concentrations and, at the time of abdominal pain, elevated ALA and PBG concentrations.

CONGENITAL ERYTHROPOIETIC PORPHYRIA AND ERYTHROPOIETIC PROTOPORPHYRIA

Submit a blood sample (EDTA) and urine sample to the laboratory for erythrocyte porphyrin screening and chromatographic quantitation. In patients with an active erythropoietic porphyria, the erythrocytes will show fluorescence on simple screening tests under ultraviolet light and the type of porphyria is easy be diagnosed by erythrocyte, plasma and urine porphyrin analysis. In addition, plasma scanning shows a typical fluorescence peak at 630 nm in EPP.