there is one concept of Window period that means if some infective micro organism enter into our body and you test on next day your report comes negative even even micro organism present  in your body. test will come positive after overturn number of day , weeks or months onky every disease and every test have different window period hiv 1 pro viral dna QUALITATIVE test has window period of 17 days that means you have to do this test only after 17 days to get accurate result HIV DUO has 3 month window period RAPID HIV ELISA AND OTHER CARD TEST HAS 6 month window period same way HBsAg, HCV and VDRL has window period of 3 month so you have to do it after 3 month of exposure.

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