Resolving the clinical dilemma of low positive HIV screening: 2-mercaptoethanol as the optimal pretreatment over polyethylene glycol precipitation to safeguard early diagnosis.

BACKGROUND

The high sensitivity of fourth-generation HIV antigen/antibody combo assays leads to a substantial number of low-positive screening results, creating a diagnostic dilemma. Guidelines suggest polyethylene glycol (PEG) 6000 or 2-mercaptoethanol (2-ME) pretreatment to resolve interference, yet their comparative performance on modern platforms remains inadequately validated.

METHODS

We retrospectively analyzed 589 initially reactive samples from 38 primary screening laboratories in Panyu District,Guangzhou (March 2024-October 2025). Derived from this cohort and supplemented for statistical power,138 validation samples were categorized into four groups: Western Blot (WB) positive group[WB(+), (n = 30)], double-negative by third/fourth generation enzyme-linked immunosorbent assay [3rd/4th ELISA (-/-),(n = 71)], WB-negative/indeterminate with positive nucleic acid test [WB(±/-)NAT(+), (n = 21)] and WB-negative/indeterminate with negative NAT[WB(±/-)NAT(-),(n = 16)]. Samples were evaluated on a Maccura i3000 analyzer before and after PEG 6000 or 2-ME treatment.

RESULTS

False-positive rates inversely correlated with cut-off Index (COI) value, reaching 96.30% in the 1.0-15.0 range.In the 3rd/4th ELISA (-/-) group, PEG 6000 and 2-ME achieved 100% and 97.18% negative conversion, respectively. Critically, in the WB(±/-)/NAT(+) subgroup (early infections), PEG 6000 erroneously eliminated true-positive signals, dropping diagnostic concordance to 42.86% (9/21). Conversely, 2-ME safely maintained 100% (21/21) concordance(p < 0.001).Although overall concordance across the entire cohort did not differ significantly (p = 0.143), this aggregate analysis masked 2-ME's vital superiority in specific subgroups.

CONCLUSIONS

2-ME pretreatment is superior to PEG 6000 for triaging low-positive HIV results, effectively reducing false positives while preserving critical early-infection signals. This simple strategy enhances the efficiency and accuracy of high-volume HIV screening.