There is no such thing as a weak positive HIV test strip result, and false positives may occur when the test strips are oxidized. HIV test strip results can be categorized as negative, positive and invalid. If the HIV test strips are left in the test for too long, beyond the time the test strips are meant to be used, the test strips may oxidize and give a false positive with 2 bars. False positives may also occur if the test strip exceeds its expiration date or is improperly stored and contaminated. The valid determination time of HIV test strips is usually 15-20 minutes after the blood is dropped into the test strip. If there is only a red line in the control area within this time period, it is usually negative. For definitive results, it is recommended that you visit the CDC for a definitive diagnosis after screening with the test strips.