The Evolution of STI Testing (eBook)

The Evolution of STI Testing: A Catalyst for Modern Diagnostic Technologies

4TH GENERATION COMBINATION ENZYME IMMUNOASSAY (EIA)

ADD PLASMA/SERUM

ENZYME DETECTION

LABELING

DETECTS IF HIV ANTIBODY OR P24 ANTIGEN IS PRESENT

+ color

HIV antigen

reagent

HIV antibody

p24 antigen

enzyme-linked HIV antigen

p24 antibody

coated well

enzyme-linked p24 antibody

DETECTS PRESENCE OF HIV ANTIBODY & P24 ANTIGEN INDEPENDENTLY

+ 2 fluorescent labels

Figure 2. Fourth-Generation Combination Enzyme Immunoassay (EIA) Fourth-generation EIAs detect both HIV antibodies and the p24 antigen in a single assay, enabling diagnosis within weeks of exposure. This schematic illustrates simultaneous antigen and antibody capture, which shortens the diagnostic window and improves early detection accuracy. Image adapted from: Daskalakis, D. (2016). HIV diagnostic testing: evolving technology and testing strategies. Top Antivir Med , 19 (1), 18-22. PMID: 21852712; PMCID: PMC6148855.

capable of processing more than 150 samples per hour, making them well-suited for centralized laboratories and large-scale screening programs. Fifth-generation systems, such as the Bio-Rad BioPlex 2200 HIV Ag-Ab assay, approved by the US FDA in 2015, further advanced the field by differentiating between HIV-1, HIV-2 and p24 antigen within a single run, reducing the need for confirmatory testing and accelerating reporting. 5 In parallel, another major milestone came in the 1990s with the introduction of rapid diagnostic tests (RDTs), which filled an essential gap in HIV testing. Based on lateral flow immunochromatog- raphy, these devices provide results in as little as 15 minutes from a fingerstick blood sample. 6 Though less sensitive than laboratory assays, RDTs revolutionized accessibility by enabling HIV screening in primary care, community outreach

and low-resource settings without the need for specialized equipment. They also paved the way for point-of-care (POC) platforms that bridged centralized testing and patient care, combining speed with improved accuracy through optimized antibody and antigen capture reagents. 7 The 2002 US FDA approval of the first rapid HIV test, together with regulatory shifts permitting use outside traditional laboratory settings, fundamentally expanded access and reshaped how HIV screening was delivered. 8 Each technological generation has progressively brought testing closer to the patient—from centralized immunoassay systems to rapid POC diagnostics and, ultimately, to fully self-administered kits. Self-testing marks the next evolution in HIV diagnostics, extending accessibility and autonomy

GENengnews.com | 29