Combination Assay Detecting both Human Immunodeficiency Virus (HIV) p24 Antigen and Anti-HIV Antibodies Opens a Second Diagnostic Window

Abstract

Fourth-generation human immunodeficiency virus (HIV) screening immunoassays reduce the diagnostic window between infection and diagnosis by the inclusion of HIV p24 antigen detection together with HIV antibody detection in the same test. We compared third- and fourth-generation HIV immunoassays and a dedicated HIV p24 antigen test for detection of a case of HIV seroconversion. This demonstrated a second diagnostic window using the fourth-generation assay due to a decline of HIV p24 antigen prior to the detection of HIV antibody. However, HIV p24 antigen was detected in the same sample by the dedicated HIV p24 antigen test, as was HIV proviral DNA. Although it is likely to be rare, this phenomenon has also been reported for other fourth-generation HIV immunoassays and has implications for the reported diagnostic windows of these assays.

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).…”

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.…”

Detection of an Acute HIV-1 Infection Case in the Last Day of Diagnostic Window through a Combination of Two Fourth-Generation Screening Assays on a Brazilian Public Healthy Institution: We Close the Window

“…This period lies between the p24 antigen detection and the anti-HIV antibody detection. 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 [15].…”