Review on Performance in screening HIV: Rapid Test vs ELISA
Approximately 36 million people are infected with human immunodeficiency virus across the world. In resource-limited settings, there seems to be a migration from ELISA to rapid tests for screening of human immunodeficiency virus. This article is focused on presenting facts that compare ELISA and rapid tests to produce a winner in terms of accuracy.
It is understood there tend to be inconsistencies when two different techniques are compared. Therefore, Western Blot, as most researchers would agree, is the most efficient of all HIV testing techniques, was brought into the experiment to confirm results and compare the performance of ELISA and rapid testing.
In testing HIV, two testing algorithms are used – parallel and serial. In parallel testing strategy, the samples are tested using two different tests i.e. rapid and ELISA. In serial testing strategy, the result of one test determines the need for another. In healthcare centers where serial testing strategy is used, the need for accuracy is paramount so as not to miss infection through false negatives and create confusion through false positives. The screening test is expected to be highly sensitive and the subsequent test is expected to be highly specific to weed out false positives and false negatives.
For this study, 787 samples were tested using both rapid testing kits and ELISA. When samples were analysed by rapid testing kits, 36 samples were found to be reactive, and 40 samples were found to be reactive as per ELISA.
When all the positive samples were processed through confirmatory test, Western Blotting, all the reactive samples obtained through ELISA were found to be reactive as well. Therefore, it is understood, four reactive samples were misdiagnosed as “HIV negative” when tested via rapid testing kits.
When all the reactive samples obtained via rapid tests were processed through the confirmatory test, western blotting, 5 samples were found to be nonreactive. Therefore, in addition to missing four reactive samples and rapid tests misdiagnosed 5 nonreactive samples as reactive.
Implications resulting from false positives and false negatives are huge as it leads to not only confusion but also poor understanding on the part of the patients receiving a reactive report. The false positives of rapid testing kits are often attributed to technical errors, mislabeling of samples, problems with components of the test devices and cross reactivity. In this experiment, both ELISA and Rapid kits were handled by technicians with the expertise to ensure handling accuracy.
Despite high sensitivity, the longer turnaround time of ELISA seems to be the problem for people undergoing HIV testing, whereas rapid tests provide an excellent option for testing immediately. The possibility of missing early infections (false negatives) is a matter of huge concern as the general population is exposed to unwarranted risks.
Following serial testing algorithm across all healthcare centers could be of greater use as preliminary report could be provided immediately (results of Rapid tests) followed by testing of all samples by ELISA to identify any false negative and false positive results. The problems posed by rapid tests can be overcome using ELISA test and western blotting as confirmatory tests. In addition, detection of p24 antigen via rapid tests would significantly enhance efficiency.