The One-Step Tetrahdrocannabinol Test is a one-step immunoassay in which a chemically labeled drug (drug-protein conjugate) competes with the drug which may be present in urine for limited antibody binding sites. The test device contains a membrane strip which is precoated with drug-protein conjugate on the test band. The colored anti-Tetrahdrocannabinol antibody-colloidal gold conjugate pad is placed at the end of the membrane. In the absence of drug in the urine, the solution of colored antibody-colloidal gold conjugate and urine moves upward chromatographically by capillary action across the membrane. This solution then migrates to the immobilized drug-protein conjugate zone to form a visible line as the antibody complexes with the drug-protein conjugate. Therefore , the formation of a visible precipitant in the test band region occurs when the test urine is negative for the drug.
When the drug is present in the urine, the drug/metabolite antigen competes with the drug-protein conjugate on the test band region (T) for the limited antibody sites on the anti-Tetrahdrocannabinol antibody-colloidal gold
conjugate. When a sufficient concentration of drug is present , it will fill the limited antibody binding sites. This will prevent attachment of the colored antibody-colloidal gold conjugate to the drug-protein conjugate zone on the test band region.Therefore, absence of the color band on the test region indicates a positive result. teaction is also to added to the test is performed properly. This control line should always appear regardless of the presence of drug or metabolite. This means that negative urine will produce two colored band, and positive urine will produce only one band. The presence of this colored band in the control region also serves as verification that ① sufficient specimen has been added, and ② that proper flow was obtained.