Ascorbic acid interference in reagent-strip reactions for assay of urinary glucose and hemoglobin

Vitamin C (ascorbic acid), commonly taken as a dietary supplement and excreted in the urine, can interfere with peroxidase redox indicator systems such as those used in reagent-strip tests for urinary glucose and hemoglobin. We investigated whether the concentrations of ascorbic acid in urine after modest supplementary doses of vitamin C are high enough to interfere with such dipstick tests. After adding glucose or hemoglobin to urine collected from persons not taking vitamin C and from persons taking 350 to 1000 mg of vitamin C daily, we tested four reagent strips for interference and found that these commonly taken doses did frequently interfere with all test systems examined.