Plasma and Urine Aminolevulinic Acid and Porphobilinogen
Related Gene(s): CPOX, HMBS, PPOX
Urinary and plasma aminolevulinic acid (ALA) and porphobilinogen (PBG) measurements are used in the clinical diagnosis and monitoring of the acute hepatic porphyrias, a group of inborn errors of heme biosynthesis. These include autosomal dominant acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), variegate porphyria (VP), and autosomal recessive ALA-dehydratase deficient porphyria (ADP). Gene mutations alone are not sufficient to produce the symptoms of these disorders. Other activating factors, such as drugs, hormones, or dietary changes precipitate the life-threatening acute neurovisceral attacks.
Acute attacks are typically characterized by severe abdominal pain. However, sometimes the pain may begin in the chest, back, or thighs. Patients also experience nausea, vomiting, constipation, and increased heart rate and blood pressure. These symptoms and signs are all due to the effects of the disease on the nervous system. Confusion, convulsions, and muscular weakness, due to neurologic impairment, may lead to paralysis. An acute attack usually lasts for days or longer. Recovery from severe paralysis is generally slow.
The diagnostic hallmark of an acute attack is the marked increase of plasma and urinary concentrations of the porphyrin precursors, ALA and PBG, particularly urinary PBG. In the three autosomal dominant acute porphyrias, ALA and PBG levels are normal or slightly increased in asymptomatic patients, but may increase 40-fold over presymptomatic levels during an acute attack. In ADP, the ALA levels are consistently elevated, but increases occur during acute attacks. Testing is performed by liquid chromatography and tandem mass spectrometry.
- Plasma: 2-3 mL of blood in sodium heparin (green top). Minimum of 0.5 mL blood (0.2 mL plasma), Draw in amber tube or protect from light by wrapping in foil. Centrifuge immediately and freeze plasma
- Urine: 5 mL (random void) in a clean container without preservatives. Minimum of 2 mL. Protect from light by wrapping in foil and freeze
- Ship overnight frozen on dry ice
- Routine: 3-5 days
- Emergency: Same day results available on an emergency basis. Please call the laboratory prior to sending a sample for STAT analysis