A reagent strip for measuring glucose concentration in a biological fluid containing red blood cells has reduced interference of hematocrit with the glucose measurement. When a biological fluid contacts the strip, it causes, in a reagent impregnated in the strip, a color change which is a measure of the glucose concentration in the fluid. However, the color change is also affected by the red blood cell concentration (hematocrit), thereby reducing the accuracy of the glucose measurement. The hematocrit effect is reduced by adding to the reagent a component, such as imidazole or imidazole and N-acetylglucosamine, for minimizing side reactions of the glucose, or its reaction products, with the fluid.