Aminolevulinic acid (ALA), a urine pigment, is the precursor to porphobilinogen (PBG) in the formation of heme of hemoglobin. Subsequent steps include: PBG leading to formation of uroporphyrinogen III/uroporphyrin III, followed by formation of coproporphyrinogen III/coproporphyrin III, then protoporphyrinogen/ protoporphyrin. This process then leads to heme formation. If a problem occurs during heme formation, the ALA accumulates and is excreted in the urine. ALA is normally absent from urine.
The presence of ALA in the urine usually indicates lead poisoning. The test can be used as a screening device for detection of excessive absorption of lead before the appearance of symptoms.
Concentrations of ALA are greatly increased in many patients with acute neurological forms of porphyrias. ALA testing may be ordered in patients with symptoms suggestive of acute porphyria, such as abdominal pain, nausea, constipation, peripheral neuropathy, muscle weakness, urinary retention, confusion, and hallucinations.
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