Abstract: A disposable indicator is disclosed which is useful for the measurement of substances, e.g., glucose, in biological fluids. The instrument registers the concentration of substance in a given biological fluid with indicia which are directly readable in a convenient notation system (e.g., digital or other symbolic notation). The indicator comprises an improvement over prior art disposable devices which require a comparison of the viewable indication with a color intensity scale to translate the indicia registered to meaningful numerical values or other symbolic notations. The indicator permits the use of chemical reagent concentrations which are at least an order of magnitude greater than those used in prior art, thereby improving stability and drastically lowering the magnitude of interferences. As an example, the use of the indicator of the invention in conjunction with novel reagent compositions in the determination of urinary glucose concentrations is disclosed.