Calcium oxalate is the predominant constituent of most
kidney stones. The rare
genetic disorder,
primary hyperoxaluria, is characterized by the continuous excessive synthesis and urinary excretion of
oxalic acid, leading to stone formation and
renal insufficiency. The earliest measurement of
oxalate in suspected cases of
primary hyperoxaluria is advantageous and would lend support for continued analysis and eventual confirmation of the disease. Therefore, we quantitated
oxalate levels in amniotic fluid (AF) using medium pressure ion-exchange chromatography. The mean concentration of
oxalate in amniotic fluid was 1.67 mg/l +/- 0.8 (SD); (range 0.64 to 5.11 mg/l). The mean
oxalate/
creatinine ratio (O/C) was 0.23 +/- 0.11 (SD); (range 0.07 to 0.53). This ratio is similar to that found in the urine of infants less than 1 year (0.19 +/- 0.10; n = 17). There was no significant difference between males and females in
oxalate concentration or O/C ratio. Regression analysis showed no significant correlation of fetal age with
oxalate, O/C or
creatinine. Studies in 13 sets of di-amnionic twins showed no statistical difference in
oxalate or O/C between twin A and B. This study demonstrates the ability to accurately quantitate
oxalate in amniotic fluid by ion-chromatography, and suggests that this may have a potential application in the initial screening process for the prenatal detection of
primary hyperoxaluria.