Synonyms: Oxalic acid
Clinical significance
Oxalic acid is an end product of the metabolism of ascorbic acid and glyoxylic acid. Most oxalic acid (80-90%) is produced by the body, but some comes from the diet (spinach, cocoa, tea, beetroot, rhubarb, tomatoes). Some workers are exposed to substances that contain it (detergents, bleaches), and it can be found as a metabolite after exposure to ethylene glycol. Oxalic acid is eliminated by the kidneys and readily precipitates; in excess it forms calcium oxalate deposits, causing tubulointerstitial nephropathy, nephrocalcinosis and kidney stones.
Clinical indications
Primary hyperoxaluria (inherited enzyme deficiencies); secondary hyperoxaluria due to increased absorption from the gut (Crohn’s disease, coeliac disease, ileal resection, pancreatic insufficiency); vitamin B6 deficiency; occupational exposure to oxalic acid and ethylene glycol.
Sample type
A 24-hour urine collection is required.
Preparation
The collection is made in a container containing hydrochloric acid, to be collected from the laboratory and used as supplied without rinsing.
Notes
Methoxyflurane, some foods and ascorbic acid can raise its concentration.