Urine Oxalate and Citrate

Purpose:
The amounts of oxalate and citrate excreted in urine and their urinary concentrations are important risk factors for the development of kidney stones. Citrate in the urine has long been recognized as an inhibitor of calcium salt crystallization and patients having low citrate levels (hypocitraturia) are at increased risk of kidney stone formation. There are several metabolic disorders associated with low urinary citrate concentrations, any condition which lowers renal tubular pH or intracellular pH, may decrease citrate, e.g. metabolic acidosis, increased acid ingestion, hypokalaemia or hypomagnesaemia.

Oxalate is measured as part of the investigation of the underlying cause of renal stone disease, either primary (endogenous oxalate overproduction due to an inherited enzyme deficiency), or secondary (e.g. due to excessive intake of oxalate or its precursors, or due to gastrointestinal disease associated with fat malabsorption. The long-term health of your kidneys depends on early diagnosis and prompt treatment of hyperoxaluria.

Scope:
This programme is designed to span both the analytical and clinically relevant range for the diagnosis and management of hyperoxaluria and hypocitraturia. The samples consist of challenging samples at low concentration for citrate as well as a panel of 6 linearly related pools produced from urine donations spiked with oxalate and citrate to span the analytical range. Each sample is distributed on 6 occasions with a minimum of 36 samples distributed over the year. The programme assesses both laboratory and method performance, including linearity, bias, within and between batch imprecision.