Method for end pointing enzyme detection methods

The present invention involves a composition and method for the determination of enzymatic activity or enzyme substrate concentration in a fluid test sample in which the enzyme catalyzes a reaction in a reagent system to provide a detectable response indicative of the concentration of the enzyme or enzyme substrate in the test sample. A measured amount of a protease capable of eliminating the enzymatic activity is included in the reagent composition, so that when a measured amount of test sample is treated, the reaction producing the detectable response will have a definite end point. The invention is particularly useful in conjunction with the determination of leucocytes in urine wherein the leukocytes are lysed to release their human leucocyte elastase which hydrolyzes a chromogenic ester to provide a phenol which then reacts with a diazonium salt to form a colored azo dye.