Abstract: A solution-based assay for determining the presence of peroxidatively-active substance in a bodily fluid is described. The solution-based assay contains a spectrophotometric substrate, a hydroperoxide, a pH 6.0-7.0 buffer, a surfactant, and a solvent such as DMSO, THF, DMF, or mixtures thereof, with the balance of the solution being water. The solution-bascd assay is particularly useful in qualitative and quantitative assays for urinary hemoglobin. Solution-based assay kits and assay methods are also described.