Evidence for a diagnostic window in fourth generation assays for HIV

Early Identification of Seronegative Human Immunodeficiency Virus Type 1 Infection with Severe Presentation

“…Furthermore, as well as having a higher sensitivity in the early seroconversion phase, the combined antigen/antibody detection assay permits the additional identification of infected patients, albeit very rarely, during the late stage of disease in patients who have antigenemia and impaired synthesis of anti-HIV antibody; for these patients, third-generation assays may give false-negative results (19). However, a second diagnostic window for combined antigen/antibody HIV assays has been reported in association with a reduction in sensitivity to antibody compared with the sensitivities of third-generation tests (4,8) and a reduction in sensitivity for antigen compared with that of the dedicated HIV p24 antigen test (18). Although this phenomenon is likely rare, such cases illustrate a sensitivity issue with the combined antigen/antibody HIV assay and emphasize the importance of additional testing and follow-up sampling for patients who have clinically suspected HIV infection but who are not reactive by the combined antigen/antibody HIV assay (18).…”

The risk of a second diagnostic window with 4th generation HIV assays: Two cases

“…3,9 Indeed, a previous study using commercially available 4th generation HIV assays reported a difference of up to 10 days in detecting antibodies when seroconversion panels were tested. 6 The existence of the second diagnostic window was already previously shown, 9,13,16,17 and certain 4th generation HIV assays appeared to be less sensitive than 3rd generation HIV assays when comparing only the antibody component. 17 The appearance of a second diagnostic window with 4th generation HIV assays was demonstrated based on a decline of HIV-1 p24 antigen prior to the detection of HIV antibody.…”

Prolonged Second Diagnostic Window for Human Immunodeficiency Virus Type 1 in a Fourth-Generation Immunoassay: Are Alternative Testing Strategies Required?

“…In contrast, studies of recent infections have reported transient sensitivities of 62% to 89% (10,11) when assessed against HIV-RNA tests. Although it is generally regarded as rare, there are many published cases where at least one fourth-generation assay has failed to diagnose an HIV-positive patient on at least one test date (4,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). In some cases, this may be due to the presence of a second diagnostic window, defined as a period where a fourthgeneration assay becomes nonreactive after the antigen component drops below the limit of detection and before the antibody component exceeds the limit of detection.…”

“…Other cases are possibly due to a primary diagnostic window caused by relative insensitivity of the antigen detection component compared with assays such as those for RNA detection (4) or for p24 antigen (14). The literature describes numerous cases where fourth-generationassay failures could conceivably be due to a second diagnostic window (10)(11)(12)(13)(14)(15)(16)(17)(18)21 Table S1 in the supplemental material). Given limitations in published sample data, many cases cannot be definitively classified.…”

“…To our knowledge, this represents the longest reported second diagnostic window for a fourth-generation assay. Further, a supplemental assay using a first-generation whole-virus lysate was assessed throughout the testing period and was positive from The second diagnostic window was described previously (15,17,18), although the lack of data in many cases limits critical appraisal. However, review of those reports shows that the failure to detect infection cannot be consistently predicted by factors such as timing postinfection, HIV-1 subtype, patient demographics, or assay manufacturer.…”