The AHD chromatographic diagnostic kit is based on the specific immuno-chemical reactions between antigen and antibody. It relies on the competition between AHD residues in the sample and the AHD immobilized on T line on the membrane for the AHD antibody-dye conjugate. Since the drug has been presenting in the sample, it will compete with the drug immobilized on T line, to the limited amount of dye-antibody. As a sufficient amount of drug in the sample is presenting, the drug will saturate the antibody. Consequently, it will show an extremely light or even invisible T line, indicating a positive result. On the other hand, if there is a negative sample (or the amount of the drug is lower than the minimum detectable concentration, 0.5 ppb), it will generate two obvious lines in both the T and C line section.

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