Real-world performance of the new US HIV testing algorithm in medical settings

A case of a false positive HIV antigen/antibody screen in a pregnant woman at delivery and the clinical importance of reviewing signal-to-cutoff ratio values

We present a unique case not previously touched upon in the literature, and its ensuing management, of a falsely reactive HIV (human immunodeficiency virus) screening test which resulted in a woman during active labor, hours after rupture of membranes. The patient was screened for HIV using the ARCHITECT 4th generation HIV 1 and 2 Antigen/Antibody (Ag/Ab) Combo assay, and the results were repeatedly reactive. A cesarean delivery was recommended, and the patient received intrapartum antiretroviral therapy. Due to rapid progression of labor, the infant was delivered vaginally and received multiple doses of antiretroviral therapy. For confirmation, a viral load PCR test was obtained which resulted undetectable, and it was concluded that the screening results were falsely positive. While the cause of the inaccurate screening result is still unclear, a COVID-19 vaccination in close proximity to the delivery remains suspicious. Four months after delivery, the patient's screening test was no longer reactive.

Review of HIV Self Testing Technologies and Promising Approaches for the Next Generation

The ability to self-test for HIV is vital to preventing transmission, particularly when used in concert with HIV biomedical prevention modalities, such as pre-exposure prophylaxis (PrEP). In this paper, we review recent developments in HIV self-testing and self-sampling methods, and the potential future impact of novel materials and methods that emerged through efforts to develop more effective point-of-care (POC) SARS-CoV-2 diagnostics. We address the gaps in existing HIV self-testing technologies, where improvements in test sensitivity, sample-to-answer time, simplicity, and cost are needed to enhance diagnostic accuracy and widespread accessibility. We discuss potential paths toward the next generation of HIV self-testing through sample collection materials, biosensing assay techniques, and miniaturized instrumentation. We discuss the implications for other applications, such as self-monitoring of HIV viral load and other infectious diseases.

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.

Performance of an Alternative Laboratory-Based HIV Diagnostic Testing Algorithm Using HIV-1 RNA Viral Load

BACKGROUND

Since 2014, the recommended algorithm for laboratory diagnosis of HIV infection in the United States has consisted of an HIV-1/2 antigen/antibody (Ag/Ab) test followed by an HIV-1/2 antibody (Ab) differentiation test and, if necessary, a diagnostic HIV-1 nucleic acid test to resolve discordant or indeterminate results.

METHODS

Using stored specimens from persons seeking HIV testing who had not received a previous diagnosis or treatment, we compared the performance of a 3-step alternative algorithm consisting of an Ag/Ab test followed by a quantitative HIV-1 RNA viral load assay and, if viral load is not detected, an Ab differentiation test, to that of the recommended algorithm. We calculated the sensitivity and specificity of 5 Ag/Ab tests and the proportion of specimens correctly classified by the alternative algorithm compared with the recommended algorithm. Results were examined separately for specimens classified as early infection, established infection, and false-reactive screening.

RESULTS

Sensitivity and specificity were similar among all Ag/Ab tests. Viral load quantification correctly classified all specimens from early infection, all false-reactive screening specimens, and the majority of specimens from established infection.

CONCLUSIONS

Although cost, regulatory barriers, test availability, and the ability to differentiate early from established infection must be considered, this alternative algorithm can potentially decrease the total number of tests performed and reduce turnaround time, thereby streamlining HIV diagnosis and initiation of treatment.

Risks of requiring a dedicated molecular specimen for HIV diagnosis and a potential strategy for mitigation

Background

HIV screening (i.e. antigen/antibody) tests are followed by a supplemental (i.e. antibody-only) if the screen is positive. Discrepant results can result from two scenarios: a false-positive screening test or acute HIV infection. These scenarios can be distinguished by a molecular HIV test, but due to contamination concerns, our laboratory recently implemented a policy requiring a second specimen dedicated for molecular HIV testing. Our objective was to (1) characterize the effect of this policy on the time-to-diagnosis for patients with discrepant screening and supplemental test results, and (2) explore “strength of positivity” as an interim predictor of screening test accuracy while awaiting confirmatory test results.

Methods

Data from our laboratory information system, electronic health record, and instrument logs were used to collate data for all HIV testing performed at Barnes-Jewish Hospital (BJH) between January 1, 2014 and October 18, 2017.

Results

Requiring a dedicated specimen for molecular testing significantly increased the time-to-diagnosis for patients with discrepant screening and supplemental HIV tests (p = 0.0084). This policy also contributed to loss-to-followup, with 0/35 discrepant cases lost-to-followup prior to policy implementation compared to 2/10 after implementation. However, by optimizing the signal-to-cutoff (S/CO) ratio of the screening test, we were able to more accurately distinguish false-positives from acute-HIV prior to molecular testing (sensitivity of 100%, specificity of 89%).

Conclusions

We propose utilizing quantitative fourth-generation assay results (S/CO) ratios as a predictor of infection true positivity in situations where the screening assay is reactive but the supplemental test is negative and confirmatory molecular results are not immediately available.

Risk stratification of HIV infection for patients needing molecular confirmation with the Abbott 4th generation Architect System

BACKGROUND

Some patients need their 4^th generation HIV testing results confirmed with molecular testing after primary confirmatory testing which may not be immediately available. Further risk stratification of these patients pending the results of molecular testing may be of value not only for patient counseling but also for treatment of women in labor.

OBJECTIVES

To determine the risk of a positive test result on molecular testing for these patients.

STUDY DESIGN

The risk of a positive molecular test result for patients with a result needing molecular confirmation on a 4th generation HIV testing algorithm (Abbott Architect, Multispot/Geenius confirmatory test) was stratified based on the patient's white blood cell (WBC) count and the magnitude of Architect result Signal Cut Off ratio (S/CO).

RESULTS

A total of 61,666 patients were tested with 658 (1.1%) positive results and 76 (0.12%) patients needing molecular confirmation. Patients with an S/CO of <5 or an S/CO of 5-100 with a WBC > 6.5 × 10 ⁹ cells/l had a significantly lower risk of a positive molecular HIV test (0/48, 0%) than patients with an S/CO 5-100 with a WBC < 6.0 s × 10 ⁹ cells/l (5/9, 56%, p < .001) or an S/CO > 100 (2/2, 100%, p < .001). Pregnant women had a significantly lower rate of positive test results (24/6924, 0.4%) than non-pregnant patients (634/54742, 1.1%, p < 0.001). All 12 cases needing molecular confirmation in pregnant women had negative NAT test results.

CONCLUSIONS

Patients who need their HIV results confirmed with molecular testing using a 4^th generation algorithm that includes the Abbott Architect System can be further stratified into low, intermediate, and high risk groups based on additional laboratory information pending the results of molecular testing. This risk stratification may be of value for patient counseling and treatment of women in labor.

Diagnostic accuracy of fourth-generation ARCHITECT HIV Ag/Ab Combo assay and utility of signal-to-cutoff ratio to predict false-positive HIV tests in pregnancy

BACKGROUND

False-positive HIV screening tests in pregnancy may lead to unnecessary interventions in labor. In 2014, the Centers for Disease Control and Prevention released a new algorithm for HIV diagnosis using a fourth-generation screening test, which detects antibodies to HIV as well as p24 antigen and has a shorter window period compared with prior generations. A reactive screen requires a differentiation assay, and supplemental qualitative RNA testing is necessary for nonreactive differentiation assay. One screening test, the ARCHITECT Ag/Ab Combo assay, is described to have 100% sensitivity and >99% specificity in nonpregnant populations; however, its clinical performance in pregnancy has not been well described.

OBJECTIVE

The objective of the study was to determine the performance of the ARCHITECT assay among pregnant women at a large county hospital and to assess whether the relative signal-to-cutoff ratio can be used to differentiate between false-positive vs confirmed HIV infections in women with a nonreactive differentiation assay.

STUDY DESIGN

This is a retrospective review of fourth-generation HIV testing in pregnant women at Parkland Hospital between June 1, 2015, and Jan. 31, 2017. We identified gravidas screened using the ARCHITECT Ag/Ab Combo assay (index test), with reflex to differentiation assay. Women with reactive ARCHITECT and nonreactive differentiation assay were evaluated with a qualitative RNA assay (reference standard). We calculated sensitivity, specificity, predictive value, and false-positive rate of the ARCHITECT screening assay in our population and described characteristics of women with false-positive HIV testing vs confirmed infection. Among women with a nonreactive differentiation assay, we compared interventions among women with and without a qualitative RNA assay result available at delivery and examined relative signal-to-cutoff ratios of the ARCHITECT assay in women with false-positive vs confirmed HIV infection.

RESULTS

A total of 21,163 pregnant women were screened using the ARCHITECT assay, and 190 tested positive. Of these, 33 of 190 (17%) women had false-positive HIV screening tests (28 deliveries available for analysis), and 157 of 190 (83%) had confirmed HIV-1 infection (140 available for analysis). Diagnostic accuracy of the ARCHITECT HIV Ag/Ab Combo assay in our prenatal population (with 95% confidence interval) was as follows: sensitivity, 100% (97.7-100%); specificity, 99.8% (99.8-99.9%); positive likelihood ratio, 636 (453-895); negative likelihood ratio, 0.0 (NA); positive predictive value, 83% (77-88%); and false positive rate, 0.16% (0.11-0.22%), with a prevalence of 7 per 1000. Women with false-positive HIV testing were younger and more likely of Hispanic ethnicity. A qualitative RNA assay (reference standard) was performed prenatally in 24 (86%) and quantitative viral load in 22 (92%). Interventions occurred more frequently in women without a qualitative RNA assay result available at delivery, including intrapartum zidovudine (75% vs 4%, P = .002), breastfeeding delay (75% vs 8%, P = .001), and neonatal zidovudine initiation (75% vs 4%, P = .002). The ARCHITECT signal-to-cutoff ratio was significantly lower for women with false-positive HIV tests compared with those with established HIV infection (1.89 [1.27, 2.73] vs 533.65 [391.12, 737.22], respectively, P < .001).

CONCLUSION

While the performance of the fourth-generation ARCHITECT HIV Ag/Ab Combo assay among pregnant women is comparable with that reported in nonpregnant populations, clinical implications of using a screening test with a positive predictive value of 83% in pregnancy are significant. When the qualitative RNA assay result is unavailable, absence of risk factors in combination with an ARCHITECT HIV Ag/Ab assay S/Co ratio <5 and nonreactive differentiation assay provide sufficient evidence to support deferral of unnecessary intrapartum interventions while awaiting qualitative RNA results.

Evaluation of the virtues and pitfalls in an HIV screening algorithm based on two fourth generation assays - A step towards an improved national algorithm

BACKGROUND

Fourth-generation immunoassays used for HIV screening, simultaneously detect anti-HIV antibodies and HIV-1 P24 antigen, but are prone to false-positive results. Usually, they are followed by highly specific third-generation assay, able to differentiate between HIV-1/2 infections. In Israel, screening algorithm is based on consecutive testing by two fourth-generation assays and confirmation by a third-generation test.

OBJECTIVES

To evaluate the performance of this algorithm.

STUDY DESIGN

Architect HIV1/2 Combo (Combo) reactive results were tested by Vidas HIV Duo Ultra (VD). Confirmation was by INNO-LIA HIV 1/2 or Geenius assays. Five-year results were retrospectively analyzed. HIV true positives (TPs), acute infected (AI), false-positives (FPs) and HIV negatives, were as defined by the algorithm.

RESULTS

501,338 individuals were screened, of which 956 were TPs, 64 AI and 30 F Ps. Specificity was almost 100% and positive predictive value 97%. VD was negative in 94% of confirmed Combo false-reactive individuals. The Combo results in the first tested sample differed substantially between TPs, AI and FPs, enabling the determination of a cutoff value that distinguished 94% of TPs and AI from FPs.

CONCLUSIONS

An algorithm is suggested that will use a single sample collection. HIV negative diagnosis will be based on Combo unreactive or Combo reactive/VD negative results. HIV positive diagnosis will be based on Combo reactive/ VD positive results, given a Combo value above a designated cutoff. Below this cutoff samples will be tested by a molecular assay. Since HIV-2 rarely occurs in Israel, the use of a third-generation confirmation assay should be discussed.

Performance of the Alere Determine™ HIV-1/2 Ag/Ab Combo Rapid Test with algorithm-defined acute HIV-1 infection specimens

BACKGROUND

The capacity of HIV Antigen/Antibody (Ag/Ab) immunoassays (IA) to detect HIV-1 p24 antigen has resulted in improved detection of HIV-1 infections in comparison to Ab-only screening assays. Since its introduction in the US, studies have shown that the Determine HIV-1/2 Ag/Ab Combo assay (Determine Ag/Ab) detects HIV infection earlier than laboratory-based IgM/IgG-sensitive IAs, but its sensitivity for HIV-1 p24 Ag detection is reduced compared to laboratory-based Ag/Ab assays. However, further evaluation is needed to assess its capacity to detect acute HIV-1 infection.

OBJECTIVE

To assess the performance of Determine Ag/Ab in serum from acute HIV-1 infections.

STUDY DESIGN

Select serum specimens that screened reactive on a laboratory-based Ag/Ab IA or IgM/IgG Ab-only IA, with a negative or indeterminate supplemental antibody test and detectable HIV-1 RNA were retrospectively tested with Determine Ag/Ab. Results were compared with those of the primary screening immunoassay to evaluate concordance within this set of algorithm-defined acute infections.

RESULTS

Of 159 algorithm-defined acute HIV-1 specimens, Determine Ag/Ab was reactive for 105 resulting in 66.0% concordance. Of 125 that were initially detected by a laboratory-based Ag/Ab IA, 81 (64.8%) were reactive by Determine Ag/Ab. A total of 34 acute specimens were initially detected by a laboratory-based IgM/IgG Ab-only IA and 24 (70.6%) of those were reactive by Determine Ag/Ab.

CONCLUSIONS

Due to their enhanced sensitivity, laboratory-based Ag/Ab IAs continue to be preferred over the Determine Ag/Ab as the screening method used by laboratories conducting HIV diagnostic testing on serum and plasma specimens.

Trends in testing algorithms used to diagnose HIV infection, 2011-2015, United States and 6 dependent areas

BACKGROUND

In 2014 the Centers for Disease Control and Prevention (CDC) and the Association of Public Health Laboratories (APHL) issued updated laboratory testing recommendations for the diagnosis of HIV infection.

OBJECTIVES

To examine trends in the use of HIV diagnostic testing algorithms, and determine whether the use of different algorithms is associated with selected patient characteristics and linkage to HIV medical care.

STUDY DESIGN

Analysis of HIV infection diagnoses during 2011-2015 reported to the National HIV Surveillance System through December 2016. Algorithm classification: traditional = initial HIV antibody immunoassay followed by a Western blot or immunofluorescence antibody test; recommended = initial HIV antibody IA followed by HIV-1/2 type-differentiating antibody test; rapid = two CLIA-waived rapid tests on same date.

RESULTS

During 2011-2015, the percentage of HIV diagnoses made using the traditional algorithm decreased from 84% to 16%, the percentage using the recommended algorithm increased from 0.1% to 64%, and the percentage using the rapid testing algorithm increased from 0.1% to 2%. The percentage of persons linked to care within 30 days after HIV diagnosis in 2015 was higher for diagnoses using the recommended algorithm (59%) than for diagnoses using the traditional algorithm (55%) (p < 0.05).

CONCLUSIONS

During 2011-2015, the percentage of HIV diagnoses reported using the recommended and rapid testing algorithms increased while the use of the traditional algorithm decreased. In 2015, persons with HIV diagnosed using the recommended algorithm were more promptly linked to care than those with diagnosis using the traditional algorithm.

Diagnosis of HIV-1 infection: Performance of Xpert Qual and Geenius supplemental assays in fourth generation ELISA-reactive samples

BACKGROUND

Architect (AR) and Vidas (VD) fourth generation HIV screening immunoassays, which identify early stages of HIV infections, could have false positive results especially at low signal/cutoff (S/C) AR values. Geenius HIV1/2 (GS) is a specific confirmation line immunoassay that is not highly sensitive to early HIV infections. An HIV-1 RNA assay may better detect such infections.

OBJECTIVES

To evaluate all AR-VD reactive samples with GS results, and to assess Xpert Qual HIV-1 RNA assay (XQ) as an alternative to GS, in the first low S/C AR-VD-reactive samples from a tested individual.

STUDY DESIGN

First AR-VD-reactive-GS-tested results from all individuals with resolved HIV status, collected between March 2015 and March 2017 (n = 749), were retrospectively assessed. Samples with AR-VD-reactive-GS-discordant results and those with low S/C AR-VD-reactive results, were tested by XQ. Receiver operating characteristic (ROC) analysis of GS and XQ sensitivity/specificity was performed.

RESULTS

Overall, 94.1% (705/749) of AR-VD-reactive results were true HIV-1 positive. All samples with <3 S/C AR values were false positive. XQ resolved all first samples with AR-VD-reactive-GS-discordant results. The diagnostic accuracy of XQ in low (≤33 S/C) AR-VD-reactive samples was better than that of GS (97.6%, 81/83 versus 73.5%, 61/83, p < 0.01). ROC analysis for low S/C AR samples was optimal for pooled XQ and GS results.

CONCLUSIONS

Incorporating XQ in the current screening algorithm for the first AR-VD-reactive-GS-discordant samples may significantly reduce overall turn-around time of HIV-1 diagnosis.