HIV serology signal-to-cutoff ratio as a rapid method to predict confirmation of HIV infection

Evaluation of a two-test strategy for HIV screening in a low-prevalence setting and the indications for optimizing clinical management

Objectives

To evaluate a two-test strategy for HIV screening in the low-prevalence population and to assess the feasibility of utilizing the optimal signal-to-cutoff (S/CO) threshold on the chemiluminescence immunoassay(CMIA) and an additional rapid test on the gold immune-chromatography assay (GICA) for screening positive patients and optimization of clinical management.

Methods

We conducted a retrospective study of samples analyzed by the fourth-generation Architect HIV Ag/Ab combo assay (CMIA) in a large medical center between June 2017 and August 2020. Reactive samples underwent a second screening test using the rapid test GICA, followed by Western blot (WB) as the confirmatory test. Receiver operating characteristic (ROC) curve analysis was used to determine the optimal S/CO. We calculated sensitivity, specificity, and predictive value based on our population. The performance of the single-test strategy (CMIA) was compared with that of the two-test strategy (CMIA and GICA). Logistic regression was used to analyze the factors of clinical characteristics leading to false positive results.

Results

A total of 220558 samples were screened by CMIA, and 429 patients met the inclusion criteria. Of these, CMIA produced 199 false-positive results with a median S/CO of 1.93(IQR1.45-3.68) and 230 positive results with a median S/CO of 455.1 (IQR169.3-709.7). The optimal S/CO of the single-test strategy was 8.82, which achieved a sensitivity of 100% and a positive predictive value (PPV) of 90.9%. The two-test strategy (CMIA and GICA) provided a sensitivity of 100% and a PPV of 98.7%, which best correlated with the confirmatory test WB. The combination of S/CO 8.82 on the CMIA assay and additional test results of GICA can be defined as four types used to interpret HIV serostatus. The false positive rate (FPR) was high in the female, the age≤18 group, the pre-operative patients, and the patients from the clinical departments of Pediatrics, Gynecology and Obstetrics, and Oncology, etc.

Conclusions

The false positive rate is high in the low-prevalence setting by using CMIA. The two-test strategy (CMIA and GICA) is recommended for HIV screening in hospitals. Hopefully, the clinicians will be able to interpret HIV serostatus and facilitate clinical decision-making while waiting for the confirmatory results.

Clinical Utility of the Signal-to-Cutoff Ratio of Reactive HIV Antigen/Antibody Screening Tests in Guiding Emergency Physician Management

BACKGROUND

The signal-to-cutoff (S/CO) ratio of the HIV antigen/antibody test may help immediately to differentiate true-positive results from false-positive results, which may be particularly useful in time-sensitive circumstances, such as when providing emergency department (ED) care.

SETTING

Seven US EDs with HIV screening programs using HIV antigen/antibody assays.

METHODS

This cross-sectional study of existing data correlated S/CO ratios with confirmed HIV status. Test characteristics at predetermined S/CO ratios and the S/CO ratio with the best performance by receiver operator characteristic (ROC) curve were calculated.

RESULTS

Of 1035 patients with a reactive HIV antigen/antibody test, 232 (22.4%) were confirmed HIV-negative and 803 (77.6%) were confirmed HIV-positive. Of the 803 patients, 713 (88.8%) experienced chronic infections and 90 (11.2%) experienced acute infections. S/CO ratios were greater for HIV-positive (median 539.2) than for HIV-negative patients (median 1.93) (P < 0.001) and lower for acute infection (median 22.8) than for chronic infection (median 605.7) (P < 0.001). All patients with an S/CO ratio < 1.58 (n = 93) were HIV-negative (NPV 100%), and nearly all with an S/CO ≥ 20.7 (n = 760) (optimal level by ROC analysis) were HIV-positive (PPV 98.6%). Of patients with S/CO values between 1.58 and 20.7 (n = 182), 29.7% were HIV-positive.

CONCLUSIONS

The S/CO ratio may be used in real time to classify most ED patients as almost certain to be either HIV-positive or HIV-negative long before nucleic acid confirmatory testing is available. When combined with clinical judgment, this could guide preliminary result disclosure and management.

An Analysis of Predictive Sample-to-Cutoff Index for HIV Infection Confirmation Using Elecsys® HIV Combi PT Assay

BACKGROUND

Early and rapid diagnosis is crucial in HIV preventing and treatment. However, the false-positive rate (FPR) by 4-th generation detection assays was high in low-HIV-prevalence regions.

OBJECTIVES

To analyze the relation between sample-to-cutoff index (COI) and HIV confirmatory results, and to explore a new COI threshold in our own laboratory to predict HIV infection.

METHODS

We retrospectively analyzed primarily reactive results by Elecsys® HIV combi PT assays and their confirmatory results by western blot (WB) at Nanjing Center for Disease Control and Prevention (CDC). The mean COI values of true positive (TP), false positive (FP), and indeterminate groups were compared, and receiver operating characteristic curve (ROC) analysis was performed to determine the optimal COI value for predicting HIV infection.

RESULTS

Totally 150,980 HIV serological results were reviewed, and 305 (0.2%) were primarily reactive. There are 82 (26.89%) true positives, 210 (71.92%) false positives, and 11 indeterminate samples confirmed by WB tests, and another 2 patients rejected WB tests. Mean COI values of TP (643.5) were greatly higher than that of FP (3.174) (P < 0.0001), but there is no significant difference between FP and indeterminate groups. Combining the requirement of HIV diagnosis and ROC analysis, 9.87 was established as the optimal threshold to predict the infection, with 100% sensitivity and 99.99% specificity.

CONCLUSIONS

By adjusting the COI threshold, the FP samples can be reduced and the efficiency of screening assays can be increased, which can save much additional reagent and staff costs and much time for delivery of HIV test results.

Novel Criteria for Diagnosing Acute and Early Human Immunodeficiency Virus Infection in a Multinational Study of Early Antiretroviral Therapy Initiation

BACKGROUND

Antiretroviral therapy (ART) initiation during acute and early human immunodeficiency virus infection (AEHI) limits HIV reservoir formation and may facilitate post-ART control but is logistically challenging. We evaluated the performance of AEHI diagnostic criteria from a prospective study of early ART initiation.

METHODS

AIDS Clinical Trials Group A 5354 enrolled adults at 30 sites in the Americas, Africa, and Asia who met any 1 of 6 criteria based on combinations of results of HIV RNA, HIV antibody, Western blot or Geenius assay, and/or the signal-to-cutoff (S/CO) ratio of the ARCHITECT HIV Ag/Ab Combo or GS HIV Combo Ag/Ab EIA. HIV status and Fiebig stage were confirmed by centralized testing.

RESULTS

From 2017 through 2019, 195 participants were enrolled with median age of 27 years (interquartile range, 23-39). Thirty (15.4%) were female. ART was started by 171 (87.7%) on the day of enrollment and 24 (12.3%) the next day. AEHI was confirmed in 188 (96.4%) participants after centralized testing, 4 (2.0%) participants were found to have chronic infection, and 3 (1.5%) found not to have HIV discontinued ART and were withdrawn. Retrospectively, a nonreactive or indeterminate HIV antibody on the Geenius assay combined with ARCHITECT S/CO ≥10 correctly identified 99 of 122 (81.2%) Fiebig II-IV AEHI cases with no false-positive results.

CONCLUSIONS

Novel AEHI criteria that incorporate ARCHITECT S/CO facilitated rapid and efficient ART initiation without waiting for an HIV RNA result. These criteria may facilitate AEHI diagnosis, staging, and immediate ART initiation in future research studies and clinical practice.

CLINICAL TRIALS REGISTRATION

NCT02859558.