Follow-up diagnostic test for HIV and HCV

All reactive primary HIV test results (eg. rapid tests) must be confirmed with a confirmatory test in the laboratory. HIV antibody assays typically have exceptionally high sensitivity and specificity compared with those of assays for other infectious diseases. That being the case, there is generally a trade-off that favors sensitivity over specificity for the primary HIV assay so as not to miss true positive specimens. Additional testing is required to resolve cases of false reactivity (that is, to rule out false positives) and to verify reactivity (that is, to rule in true positives).

According to WHO, retesting is recommended for the following populations:

• Individuals testing HIV - negative who:
  • have ongoing risk for HIV infection.
  • can identify a specific incident of possible HIV exposure in the preceding four weeks.
  • are pregnant, in high HIV prevalence setting; or those who test HIV negative in the first trimester, during labour or shortly after delivery.
• Individuals whose HIV status is inconclusive, irrespective of risk.
• Individuals diagnosed HIV - positive should be retested to verify their HIV diagnosis prior to initiation of care and/or treatment.

What does a negative HIV-antibody test result mean?

A negative result means either that person tested do not have HIV infection and can not transmit HIV infection to others or that too short time has elapsed from the infection and antibodies have not yet developed (less than 3 months). In the latter case, the person can transmit the infection to others. A negative antibody result does not mean that person is immune to infection.

What does a positive HIV - antibody test result mean?

A primary HIV-antibody positive result means that a confirmatory test should be done to make sure that the screening test result was correct. If the confirmatory test is also positive, it means that the person has HIV infection and can transmit HIV infection to others. People living with HIV are at risk to develop AIDS or other HIV related complications if they do not start ARV treatment.

Follow-up diagnostic test for HCV

If a test is positive for HCV antibodies, a nucleic acid test for HCV ribonucleic acid (RNA) is needed to confirm chronic infection. This because about 15–45% of people infected with HCV spontaneously clear the infection by a strong immune response without the need for treatment and have HCV antibodies even though the virus is no longer in their bodies. Although no longer infected, they will still test positive for HCV antibodies.