Porphyrin tests are assays that are used to help diagnose and monitor a group of rare disorders called porphyrias. Most porphyrin tests detect and measure by-products of the haem synthesis pathway; haem forms part of haemoglobin (the protein inside red blood cells that allows transport of oxygen). The synthesis of haem is a step-by-step process that requires the sequential action of eight different enzymes. If there is a…Porphyrin tests are assays that are used to help diagnose and monitor a group of rare disorders called porphyrias. Most porphyrin tests detect and measure by-products of the haem synthesis pathway; haem forms part of haemoglobin (the protein inside red blood cells that allows transport of oxygen). The synthesis of haem is a step-by-step process that requires the sequential action of eight different enzymes. If there is a deficiency in one of these enzymes, a bottleneck forms and precursors build up in the body’s fluids and tissues. These precursors are removed from the body in urine and faeces. The precursors that build up are dependent on where the bottleneck is occurring in the pathway i.e. on which enzyme is deficient. There are eight porphyrias, and each one is associated with a different enzyme deficiency. Most porphyrias are inherited (autosomal dominant) and result from a faulty gene. This results in about a 50% reduction in the activity of the haem-related enzyme. Enough haem is synthesised to prevent the affected person from becoming anaemic, but a large excess of one or more precursors is produced. Porphyrias may be classified according to 1. The affected enzyme2. The part of the body where the excess porphyrins are produced:Hepatic – associated with the liver Erythropoietic – associated with red blood cell production 3. Signs and symptoms of the disease (either an acute porphyria (severe abdominal pain), cutaneous porphyria (skin sensitivity to sunlight) or some porphyrias have both symptoms and signs. The acute porphyrias cause acute attacks that are associated with severe abdominal pain, vomiting, nausea, constipation, depression, confusion, hallucinations, and fits. An acute attack usually lasts for no longer than one or two weeks. Attacks may be triggered by a variety of drugs (such as anticonvulsants, antibiotics, and hormones) and environmental factors (such as dietary changes, stress, and exposure to toxic substances). The cutaneous (skin) porphyrias give sensitivity to sunlight on exposed areas of the skin (photosensitivity). Sunlight exposure, even through a glass window, has a toxic effect on the patient’s skin. This may cause redness, swelling, and a burning sensation in some patients, while in others it leads to blistering, skin thickening, hyperpigmentation (darkening of the skin), and in some cases scarring. Acute porphyrias include:Acute intermittent porphyria (AIP), the most common of the acute porphyrias ALA-dehydratase deficiency porphyria (ADP – also called plumboporphyria), which is an extremely rare condition and in the few cases described is similar to AIP Acute porphyrias with skin symptoms include:Variegate porphyria (VP), which is quite rare in the UK, but is particularly common in South African individuals of Dutch descent Hereditary coproporphyria (HCP) Cutaneous (skin) porphyrias include: Porphyria cutanea tarda (PCT), the most common of the skin porphyrias; unlike the other porphyrias it may not be inherited and most cases are due to an acquired enzyme deficiency which is triggered by liver dysfunction Erythropoietic protoporphyria (EPP), which typically begins in childhood or adolescence; sun-exposed skin turns red accompanied by burning and itching, but scarring is uncommon. X-linked erythropoietic protoporphyria (XLEPP), is clinically similar to EPP Congenital erythropoietic porphyria (CEP), which is the rarest of the porphyrias (autosomal recessive disorder); over time, extreme photosensitivity leads to extensive and severe scarring of light-exposed areas Individual Tests Clinical laboratories measure porphyrins and their precursors in urine, blood, and faeces. These tests are listed below:Porphobilinogen (PBG) in urine and delta-aminolaevulinic acid (ALA) in urine Porphyrins and precursors in urine, faeces, or blood Specialised centres can offer genetic mutation analysis on patients with an unequivocal diagnosis of porphyria or patients who have a family member with a previous, confirmed diagnosis of porphyria. How is the sample collected for testing? The sample collected depends on the porphyrin tests being requested. It may be one or more of the following:A blood sample obtained by inserting a needle into a vein in the arm A random urine sample A fresh stool sample that is not contaminated with urine or water Samples must be protected from light after collection. See MoreSee Less
