During a test labeled antibody-dye conjugate mixes with urine specimen and binds to the free drug if it is presented in the sample, to form an antibody-antigen complex. This complex prevents the formation of pink color bands in the test zone of the dip-stick if drug to be detected in specimen is above the detection levels (300 ng/ml for Morphine). In case of absent of drug and its metabolites, unbound dye conjugate will bind to the antigens immobilized in the test zone to form a pink reaction line. To serve as a quality control for the assay, another pink line will always appears in the test zone regardless positive or negative result.