Detection of HIV, HBV and HCV infections and diagnosis is mainly based on immunological assays among which ELISA and rapid tests are most common and widespread methods [23, 24]. An important problem encountered at this point is the discordance between the results of two assays , which can be resolved depending on the availability of suitable kits. Hence, kit evaluation gains importance for determining the diagnostic kits of better performance. Though ELISA assay shows a high degree of sensitivity, it is costly and time taking job, so rapid tests become a good alternative for ELISA in blood banks and other testing laboratories in course of time . Moreover, uses of synthetic antigens in some rapid kits have increased the specificity . Performance of rapid test would be satisfactory with a high PPV and lower degree of false negatives .
This study revealed a higher PPV in rapid tests along with better efficiency (100%) than ELISA in most of the cases except for HIV comb and HCV Comb- J. Mitra & Co. Pvt. Ltd. revealed 99.3% and 98.0% efficiency respectively. Although for a diagnostic test, the PPV and NPV will change as the prevalence of the target condition changes in the tested population. Thus, the J. Mitra & Co. HCV ELISA kit would project a PPV of 6.6%, 41.7% and 22.2% for global population with 0.8% HIV, 5% HBV and 2% HCV prevalence respectively. 4th generation HCV-comb with unique combination of modified HCV antigens have failed to show better result in this study with lowest efficiency and sensitivity (95.5%) than two other HCV rapid kits, therefore use of this type of kit in blood banks should be avoided.
HIV comb with recombinant antigens have also shown much less sensitivity (98.3%) than other HIV rapid kits evaluated, whereas, the uses of synthetic peptides along with recombinant antigen have given an added advantage to Combaids RS Advantage (22) with a better performance than HIV-comb. SD BIOLINE HIV 1/2 3.0 Rapid have also shown better result with 100% sensitivity. So, considering these parameters, HIV comb is not an appropriate kit for blood banks and ICTCs in terms of its lower sensitivity than other HIV rapid kits.
The HIV ELISA kits manufactured by SPAN Diagnostics Ltd. were revealed poor performance than the other HIV ELISA kits in terms of specificity and overall efficiency of those kits was also poor (99.3%). This was also true for Microscreen HBsAg ELISA kits (98.7%) but, in case of HCV ELISA kits, HCV Microlisa were also shown lower efficiency (93.3%) along with INNOVA HCV ELISA (96.7%).
Present study also showed lot to lot variation in performance of some kits. Mostly it was found in HCV Microlisa, Enzaids HIV 1 + 2 ELISA, Micro screen HBsAg ELISA, Innova HCV ELISA, HIV-EIA Comb and HCV-Comb.
It was found that the kit efficiency didn’t varies significantly among three different kit companies and their lots in all the cases except for HCV ELISA showing statistically significant variation (p < 0.01) among three kit types. According to present study, Hepacard, Combaids RS- Advantage-HIV, Crystal HBsAg, Signal HCV, SD BIOLINE HIV Â½ 3.0 Rapid, SD BIOLINE HBsAg Rapid and SD BIOLINE HCV Rapid are the recommended rapid kits demonstrating good performance whereas, Microlisa HIV, ERBA LISA HIV1 + 2, ERBA LISA Hepatitis B, ERBA LISA HCV and Hepalisa (HBsAg) are most acceptable ELISA kits with no false positive results. It is needed to mention that present study was performed with serum samples; therefore, performance of rapid tests may vary if whole blood sample is used as done in the point of care. As per overall results decipher, rapid tests are more acceptable than ELISA for its specificity But, ELISA proved to be more superior to rapid tests in terms of sensitivity. In case of diagnosis of infectious disease, discordant results may have serious consequences among the patients as it causes unnecessary mental stress and tension. For proper diagnosis of infection as well as disease management and prevention, identification of appropriate test kit is necessary. According to this kit evaluation, a higher number of false positive results obtained in Microlisa HCV, Innova HCV ELISA and Microscreen HBsAg ELISA which is really a matter of concern. Again, false negative results leave a threat of silent transmission and spreading of diseases among people as produced by rapid HCV-comb and HIV-comb assay and also create an urge for sensitive assays like ELISA. Therefore, in resource poor setting where ELISA is unavailable, practice of using rapid kits for blood banks may lead to spread of the deadly infection.
The HIV and HCV kits detect only IgG and thus miss the IgM which is a critical marker of early infection. Testing with these kits might lead to false negative for samples of recent infection. Therefore, the tests are subject to the serious limitation which might affect a small fraction of samples analyzed. Kits able to capture both IgM and IgG needed to be developed to reduce the chance of false negative and eventually helping in fight against the pathogens.