The basic principle behind an HIV rapid immuno-chromatographic test is that HIV-antigens placed on the test-strip will react with Anti-HIV antibodies (if there are any) from the blood. That reaction becomes visible as a colored line next to the control line. The reaction between antigens and antibodies (if there are any) requires 5-15 minutes to become visible depending upon the concentration of the antibodies in the blood (if present). However, if the test does not show a control line, the result is not valid.

The producers of the IV rapid immuno-chromatographic test say that the resulting interpretation after 20 minutes is also not valid unless the room temperature is under 15oC. In your case the test result after 20 min. was negative but became “positive” after 7 hours. That “positive” result is not valid. Your test result was NEGATIVE.

I assume that the reason the test results are not valid after 20 minutes is that after time, another factor in the the blood can precipitate and create a line that can be similar to the line created by antibody-antigen reaction. Further, the line created by an antibody-antigen reaction can also disappear in time because links between antigens and antibodies can get weak. But this hypothesis has not been confirmed by the manufacturers.


hiv rapid immunocromatographic test result - why is there a time limit?