HIV rapid tests (RTs) have been widely adopted mainly to increase the number of people who are aware of their HIV status and to provide opportunities for faster linkage to care and treatment for those infected [1–3]. RTs are simple and easy to use, can be performed on different sample types, have fast result turn-around times (usually less than 30 min), and can be used in many settings since they do not require sophisticated equipment.

In the U.S. market, seven Food and Drug Administration (FDA)-approved RTs for detection of HIV antibodies were available prior to the approval of the CHEMBIO DPP^® HIV-1/2 assay (DPP^® HIV) in December 2012. DPP^® HIV is the first RT approved in the U.S. that incorporates the dual path platform (DPP) technology. Although the DPP^® HIV received the Clinical Laboratory Improvement Amendments (CLIA) waiver in 2014, this test had been used, mainly with oral fluid (OF), outside of the U.S. since 2009 [4,5]. In addition, in 2013, a RT that detects and distinguishes between HIV antigen and antibody was approved in the US.

The DPP^® HIV is a single-use immunochromatographic RT approved for HIV antibody detection with OF, whole blood, serum, or plasma specimens. It employs a combination of antibody binding protein, which is conjugated to colloidal gold dye particles and HIV-1/2 antigens, which are bound to the membrane solid phase. Because of the DPP technology, it contains two wells, one for sample addition and another for the running buffer, which allows the sample and running buffer to flow in two different directions. The sample is added to the SampleTainer™, a bottle containing 1 ml of sample diluent buffer. After mixing, two drops (~65 μl) are dispensed in the first well allowing sample conversation for further testing if needed. After the sample has migrated to the test strip (5 min), the running buffer is added to the second well and allows reagents to flow over the antigen coated strip containing the specimen. In the presence of HIV antibodies, a dye conjugated-immune complex is formed on the HIV antigens immobilized on the membrane. A control line that contains anti-human immunoglobulin G is present to ensure that the sample and reagents have been properly applied. Since the DPP^® HIV is approved for multiple specimen types, each kit contains disposable sample loops for whole blood, plasma and serum specimens, OF swabs, and SampleTainerTM and running buffer bottles [6].

Although the DPP^® HIV can be used with different specimen types and studies have reported very good sensitivity and specificity for DPP^® HIV using OF and whole blood [4,5,7–9], no study has been conducted in early infections and/or using plasma specimens. Results using plasma specimens have been limited to the manufacturer’s clinical trials which reports 99.9% sensitivity for HIV-1 and 99.5% for HIV-1 non-B subtypes, 100% sensitivity for HIV-2, and 99.9% specificity [6].

To evaluate the performance of the DPP^® HIV using subsets of plasma specimens characterized in four different studies performed at CDC from individuals with HIV-1 and HIV-2 established infections, uninfected individuals, and HIV-1 seroconverters [10–13].

After approval by FDA, this is the first performance evaluation of the CHEMBIO DPP^® HIV-1/2 assay among well-characterized plasma specimens showing that overall HIV-1 and HIV-2 sensitivities and specificity were within the reported values in the package insert [6]. Results from field evaluations in Nigeria and Mozambique indicate that the assay performs well in OF and whole blood [4,8] specimens from these countries which predominantly have subtypes A, C, CRF-02 AG, and G. Cameroon specimens of these subtypes were also detected using plasma in our study. However, a recent study showed a lower sensitivity in OF among specimens with low viral load and/or high CD4 counts [5]. DPP^® HIV detected all HIV-2 specimens (group A and B) from Ivory Coast, so despite the fact that the assay does not distinguish between HIV-1 and HIV-2, detection of HIV-2 is not a problem.

In early HIV-1 infections, the analysis of the sensitivity relative to other RTs using the same sample set was limited to RTs that detect HIV antibody only that were available from previous evaluations. No comparison was done with the Determine^™ HIV-1/2 Ag/Ab Combo RT which detects and distinguishes HIV antigen and antibody and has been shown to detect more early infections than any other RTs in the same specimen set [12]. DPP^® HIV performs similarly to other antibody RTs that are flow through (Reveal) or lateral flow (Stat-Pak and Unigold). However, the analysis in longitudinal samples from seroconverters showed that DPP^® HIV detected antibodies against HIV-1 significantly earlier in the infections than Oraquick, which is less sensitive than other RTs in the cumulative frequency analysis. One of the limitations of the analysis that may have contributed to the differences observed in test reactivity during early infection is that in some cases not every RT result remained reactive after the first reactive result. In addition, testing in early stages of infection challenges the analytical sensitivity of any assay. In this case, negative results from singlet testing (which represents clinical sensitivity) in the seroconversion panels may reflect that the sample contains levels of antibodies that are close to the threshold of the assay’s analytical sensitivity thus missed by the assay and may be detected if repeated. However, the performance of the DPP^® HIV, an IgG-only RT that requires 10 μl of serum or plasma, was not substantially different compared to other RTs that either require approximately 2.5 times more sample volume (Multispot) or detect IgM and IgG (Unigold). Another limitation of the study is that no data in the same sample set were available for comparison with INSTI™ HIV-1 Antibody Test (bioLytical, Richmond, BC, Canada), another flow through FDA-approved RT.

It is desired for new HIV assays to improve detection of early infections so that infected persons can be linked to care and treatment. According to the manufacturer, the DPP format is designed to improve sensitivity by separating sample and reagent flow. Previous reports have shown that the assay performs well in high- and low-risk populations from Nigeria, Mozambique and the U.S. using OF or whole blood [4,7–9]. However, published data also suggest that the performance of the DPP^® HIV with OF from individuals in early stages of infection or on antiretroviral therapy may not be as sensitive [5]. In our study with plasma specimen, despite the earlier detection of HIV-1 antibodies by Multispot, the FDA-approved DPP^® HIV RT has a sensitivity similar to most FDA-approved antibody-based RTs in early and established HIV infections when used with serum and plasma specimens. Furthermore, our data show similar performance characteristics for plasma samples (subtype-B, non-subtype B and seroconversion panels) to that reported in the current DPP^® HIV package insert. Additional studies to evaluate its performance at point-of-care, especially with whole blood and OF from individuals in early stages of infection or on antiretroviral therapy, are needed to further characterize this assay.