Effect of large-dose ascorbic acid on the two-drop clinitest determination.

A study was conducted to determine if high doses of ascorbic acid would affect the two-drop Clinitest determination for glucosuria in normal individuals. Numerous secondary literature sources indicate that large doses of ascorbic acid may cause a false positive Clinitest result. Three-gram and nine-gram doses of ascorbic acid following two dosing schedules (once daily and three times daily) were taken by nine normal individuals to determine if the renal excretion of large enough quantities of ascorbic acid or its metabolites would produce false positive results with the two-drop Clinitest procedure. Each dose was given for seven days in each schedule. There were only two (0.27%) trace positive Clinitest determinations reported out of 748 Clinitest determinations. High doses of ascorbic acid in normal individuals do not appear to affect the two-drop Clinitest determination for urinary glucose. The study indicates a need to be cautious about secondary literature references on drug-laboratory test interferences.