Plasma and urine measurements for monitoring of treatment in the primary hyperoxaluric patient

Reliable methods for the assaying of oxalate in biological fluids are now available. However, preanalytical sample collection and storage conditions are critical to produce meaningful results for the diagnosis and assessment of treatment modalities in primary hyperoxaluria. Spontaneous in vitro generation of oxalate from ascorbate is possible, especially in plasma measurements, where the ascorbate to oxalate ratio is considerably greater than that of urine. The pH of blood also favours the conversion of ascorbate to oxalate. Losses, as well as generation of oxalate can occur in urine when collection procedures are inadequate. Analysis of properly collected samples is of greater assistance in monitoring the efficacy of treatment modalities in oxaluric patients. Routine and reliable assays are still needed for other closely related organic acid anions such as glycolate and L-glycerate. Measurement of these anions can facilitate the diagnosis and assist in monitoring of treatment in the different forms of primary hyperoxaluria.