Objective To differentiate between "indeterminate" early and late HIV infection samples to ensure timely follow-up.

Methods A retrospective analysis was conducted on all "indeterminate" HIV infection samples from the Pudong New Area confirmatory laboratory between 2014 and 2019. Samples were grouped based on epidemiological data and follow-up results: 58 "early positive-indeterminate"and 31 "late positive-indeterminate"samples. Fourth-generation rapid diagnostic tests (RDTs) and third-generation enzyme-linked immunosorbent assays (ELISAs) were performed on both groups. The characteristics of the screening results and confirmatory bands were analyzed, and the differences in CD4⁺T cell levels before and after 3 years of treatment were compared between the two groups.

Results Both the fourth-generation RDT and third-generation ELISA antibody tests were 100% positive in both the "early positive-indeterminate" and "late positive-indeterminate" groups. However, the S/CO values from the third-generation ELISA showed a statistically significant difference between the two groups (t=31.65, P<0.001). The proportions of different band patterns in the antibody confirmatory test that transitioned to "early positive" and "late positive" were also statistically significant (χ²=65.10, P<0.001). The overall distribution of changes in CD4⁺T cell counts before and after 3 years of treatment differed significantly between the "early positive-indeterminate" and "late positive-indeterminate"groups (U=415.5, P<0.001).

Conclusions Combining screening results and confirmatory band characteristics can effectively distinguish different stages of infection in "indeterminate" HIV antibody results and provide corresponding follow-up recommendations. Furthermore, changes in CD4⁺T cell counts before and after treatment can be used to assess immune reconstitution following treatment.