Glycolic acid in urine. A colorimetric method with values in normal adult controls and in patients with primary hyperoxaluria.

An improved Chromotropic acid-sulfuric acid assay for urinary glycolic acid is described. The sample (0.5 ml or less) is precleaned by filtering through strongly acidic and strongly basic ion-exchangers and compared with a standard made up in normal urine. From the many compounds tested, only glyceric acid in pathologically high concentrations interfers partially; this interference can be recognized at 776 nm and eliminated by a second determination. Per man-day, 8--12 samples can be analyzed. Recovery of 0.8 mmol/l glycolic acid added to the urines of 12 persons was 100.6 +/- 4.7% (1 S.D., n=12) without, and 101.9 +/- 5.3% (1 S.D., n=12) with correction for isotope dilution of [1-14C]glycolic acid, respectively, using 0.5-ml sample volumes. The variation coefficients of a single determination were 1.5 and 2.1% without and with correction for isotope dilution, respectively (n=7). The method was checked by mass fragmentography. The following normal values were found in adults (n=15; x +/- 1 S.D. (range)): 47.3 +/- 10.1 (24.4--63.7) mmol/mol creatinine and 0.60 +/- 0.15 (0.29--0.91) mmol/day or 45.8 +/- 11.3 (22.2--69.0) mg/day. Two patients (F.G. and A.S.) with primary hyperoxaluria type I excreted glycolic acid between 112 and 379 mmol/mol creatinine and 1.21--5.64 mmol/day or 92--429 mg/day. Under vitamin B-6 treatment, urinary excretion decreased in one patient (F.G.) to 71--131 mmol/mol creatinine and 0.92--2.0 mmol/day or 70--152 mg/day.