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

Abstract Background Despite the improved sensitivity of the 4th generation combined antigen/antibody HIV assays, detection of HIV in the early phase of an infection may still be ineffective. Objectives Description of two cases that highlight the existence of the “second diagnostic window phase” observed with commonly used sensitive 4th generation HIV assays. Study design Samples were screened with different 4th generation HIV assays. HIV infection was confirmed with an HIV I/II antibody assay, a HIV-1 p24 antigen assay, the INNO-LIA HIV I/II Score Line immunoassay and HIV-1 PCR. Results In both investigated cases, the limitations of the 4th generation HIV assays within the second diagnostic window were apparent. Conclusions The overall sensitivity of the commercial 4th generation HIV assays is currently higher than the 3rd generation HIV assays. Nevertheless, the rare occurrence of a second diagnostic window with 4th generation HIV assays strongly suggests that the following up testing algorithms need to be adjusted accordingly.