A diagnostic test kit for detecting the presence or quantity of an enzyme or enzyme inhibitor is provided. The diagnostic kit utilizes reactive complexes to facilitate the detection of the enzyme or enzyme inhibitor. The reactive complexes include a substrate joined (e.g., covalently bonded, physically adsorbed, etc.) to a reporter and magnetic substance. In one embodiment, for example, a peptide, protein, or glycoprotein substrate is joined to a reporter (e.g., dyed latex particle) and magnetic particle. In this embodiment, the substrate provides a cleavage target for a proteolytic enzyme. Specifically, upon contacting the reactive complexes, the proteolytic enzyme cleaves the substrate and releases the reporter and/or magnetic particle. The signal exhibited by the released reporters may then be used to indicate the presence or quantity of an enzyme or enzyme inhibitor within the test sample.