ANNALS EXPRESS: Best practice guidelines on first line laboratory testing for porphyria.

The porphyrias are disorders of haem biosynthesis which present with acute neurovisceral attacks or disorders of sun-exposed skin. Acute attacks occur mainly in adults and comprise severe abdominal pain, nausea, vomiting, autonomic disturbance, central nervous system involvement and peripheral motor neuropathy. Cutaneous porphyrias can be acute or chronic presenting at various ages. Timely diagnosis depends on clinical suspicion leading to referral of appropriate samples for screening by reliable biochemical methods. All samples should be protected from light. Investigation for an acute attack: center dot Porphobilinogen (PBG) quantitation in a random urine sample collected during symptoms. Urine concentration must be assessed by measuring creatinine, and a repeat requested if urine creatinine <2 mmol/L. center dot Urgent porphobilinogen testing should be available within 24h of sample receipt at the local laboratory. Urine porphyrin excretion (TUP) should subsequently be measured on this urine. center dot Urine porphobilinogen should be measured using a validated quantitative ion-exchange resin-based method or LC-MS. center dot Increased urine porphobilinogen excretion requires confirmatory testing and clinical advice from the National Acute Porphyria Service. center dot Identification of individual acute porphyrias requires analysis of urine, plasma and faecal porphyrins. Investigation for cutaneous porphyria: center dot An EDTA blood sample for plasma porphyrin fluorescence emission spectroscopy and random urine sample for TUP. center dot Whole blood for porphyrin analysis is essential to identify protoporphyria. center dot Faeces need only be collected, if first-line tests are positive or if clinical symptoms persist. Investigation for latent porphyria or family history: center dot Contact a specialist porphyria laboratory for advice. Clinical, family details are usually required.