Relevance of cutoff on a 4th generation ELISA performance in the false positive rate during HIV diagnostic in a low HIV prevalence setting.

BACKGROUND

Despite the high specificity of fourth-generation enzyme immunoassays (4th-gen-EIA) for screening during HIV diagnosis, their positive predictive value is low in populations with low HIV prevalence. Thus, screening should be optimized to reduce false positive results.

OBJECTIVES

The influence of sample cutoff (S/CO) values by a 4th-gen-EIA with the false positive rate during the routine HIV diagnosis in a low HIV prevalence population was evaluated.

STUDY DESIGN

A total of 30,201 sera were tested for HIV diagnosis using Abbott Architect HIV-Ag/Ab-Combo 4th-gen-EIA at a hospital in Spain during 17 months. Architect S/CO values were recorded, comparing the HIV-1 positive results following Architect interpretation (S/CO≥1) with the final HIV-1 diagnosis by confirmatory tests (line immunoassay, LIA and/or nucleic acid test, NAT). ROC curve was also performed.

RESULTS

Among the 30,201 HIV performed tests, 256 (0.85%) were positive according to Architect interpretation (S/CO≥1) but only 229 (0.76%) were definitively HIV-1 positive after LIA and/or NAT. Thus, 27 (10.5%) of 256 samples with S/CO≥1 by Architect were false positive diagnose. The false positive rate decreased when the S/CO ratio increased. All 19 samples with S/CO ≤10 were false positives and all 220 with S/CO>50 true HIV-positives. The optimal S/CO cutoff value provided by ROC curves was 32.7. No false negative results were found.

CONCLUSIONS

We show that very low S/CO values during HIV-1 screening using Architect can result HIV negative after confirmation by LIA and NAT. The false positive rate is reduced when S/CO increases.