Validation of the Elecsys® HIV combi PT assay for screening and reliable early detection of HIV-1 infection in Asia

The evaluation of low cut-off index values of Elecsys® HIV combi PT assay in predicting false-positive results

Objective

To analyze the results of different cut‐off index (COI) values of Elecsys^® HIV combi PT assay and to assess the role of COI in reducing the frequency of false‐positive results.

Methods

We conducted a retrospective study of samples analyzed by Elecsys^® HIV combi PT assay, a 4th‐generation ECLIA, between 2016 and 2017. A total amount of 379 122 samples were collected for HIV (Human Immunodeficiency Virus) screening.

Results

A total of 379 122 samples were analyzed. 2528 (0.67%) were positive by Elecsys^® HIV combi PT. Of these, 468 were false‐positive results, and most of them (94.87%) were in samples with 1 < COI < 15. The false‐positive rate was 0.12%. Patients with false‐positive samples were more distributed in elder (P < .001) and female (P < .001) than true‐positive specimens. The median COI in true‐positive specimens was (385.20), which is significantly higher than false‐positive specimens (2.08). The consistency between Elecsys^® HIV combi PT assay and 3rd‐generation and positive predictive value (PPV) increased with higher COI values. Cancer, infection, and neurological diseases were considered the potential confounding factors of HIV false‐positive results (19.44%, 11.11%, and 6.62%, respectively).

Conclusion

Samples with low COI values, especially those contain confounding factors, need to be further scrutinized to determine whether the confounding factors may cause false‐positive problem. In addition, the hypothesis that low COI values may predict false‐positive results is valid.

Analytical and Clinical Performance Evaluation of the Elecsys HIV combi PT Assay on the cobas e 602 Analyzer for the Diagnosis of Human Immunodeficiency Virus

OBJECTIVES

We evaluated the performance of the Elecsys HIV combi PT assay on the cobas e 602 analyzer for diagnosing human immunodeficiency virus (HIV; part of the US Food and Drug Administration [FDA] submission).

METHODS

The HIV combi PT and reference (ARCHITECT HIV Ag/Ab Combo) assays were assessed at four independent clinical laboratories/one reference laboratory (United States; July 2014 to November 2015). Clinical performance was evaluated using four reagent lots. Analytical performance was evaluated per Clinical and Laboratory Standards Institute EP05-A3 guidelines. Serum/plasma samples from 18 clinical sites/vendors (United States and outside the United States) were tested.

RESULTS

Sensitivity (95% confidence interval [CI]) in HIV-1 antibody-positive individuals (United States and outside the United States; n = 1,460) was 100.00% (99.75%-100.00%). Specificity was 99.94% (95% CI, 99.85%-99.98%) in low-risk individuals (United States; n = 6,843), 98.19% (95% CI, 96.93%-99.04%) in high-risk individuals (United States and outside the United States; n = 758), and 97.43% (95% CI, 95.32%-98.76%) in pregnant women (United States and outside the United States; n = 440). Analytical performance was acceptable.

CONCLUSIONS

We demonstrate the robustness of the FDA-approved Elecsys HIV combi PT assay on the cobas e 602 analyzer for HIV testing in the United States.

Specificity of two HIV screening tests detecting simultaneously HIV-1 p24 antigen and antibodies to HIV-1 and -2

This study aimed at assessing the specificity of the Elecsys^® HIV combi PT in comparison to the ARCHITECT^® HIV Ag/Ab Combo. With both of these assays, 3997 unselected sera from patients of a tertiary health care centre in Basel, Switzerland, were screened for HIV. Reactive sera were reanalysed on the VIDAS^® HIV Duo Ultra to identify false-reactive specimens prior to confirmation by quantitative PCR and line immunoassay. The Elecsys^® compared to the ARCHITECT^® shows a similar specificity (99.7% versus 99.8%) but a slightly lower positive predictive value (71.8% versus 80%). Samples tested with a cut-off index (COI) between 0.91 and 4.85 (cut-off <0.9) with the Elecsys^® and with a signal to cut-off index (S/CO) between 1.09 and 12.49 (cut-off <1.0) with the ARCHITECT^® were false-reactive. There was no false-reactive result with the VIDAS^®. Of the false-reactive samples, 66.7% could be related to patient-specific underlying conditions. The HIV two-tiered diagnostic algorithm proposed in this work improved the positive predictive values of the Elecsys^® or ARCHITECT^® to 100% when the results of the VIDAS^® were included. Values just above the cut-off are highly suspicious to be false-reactive and high COI or S/CO ratios are associated with true positivity.

Contamination with HIV antibody may be responsible for false positive results in specimens tested on automated platforms running HIV 4th generation assays in a region of high HIV prevalence

INTRODUCTION

In South Africa where the prevalence of HIV infection is very high, 4th generation HIV antibody/p24 antigen combo immunoassays are the tests of choice for laboratory based screening. Testing is usually performed in clinical pathology laboratories on automated analysers. To investigate the cause of false positive results on 4th generation HIV testing platforms in public sector laboratories, the performance of two automated platforms was compared in a clinical pathology setting, firstly on routine diagnostic specimens and secondly on known sero-negative samples.

METHODS

Firstly, 1181 routine diagnostic specimens were sequentially tested on Siemens and Roche automated 4th generation platforms. HIV viral load, western blot and follow up testing were used to determine the true status of inconclusive specimens. Subsequently, known HIV seronegative samples from a single donor were repeatedly tested on both platforms and an analyser was tested for surface contamination with HIV positive serum to identify how suspected specimen contamination could be occurring.

RESULTS

Serial testing of diagnostic specimens yielded 163 weakly positive or discordant results. Only 3 of 163 were conclusively shown to indicate true HIV infection. Specimen contamination with HIV antibody was suspected, based on the following evidence: the proportion of positive specimens increased on repeated passage through the analysers; viral loads were low or undetectable and western blots negative or indeterminate on problem specimens; screen negative, 2nd test positive specimens tested positive when reanalysed on the screening assay; follow up specimens (where available) were negative. Similarly, an increasing number of known negative specimens became (repeatedly) sero-positive on serial passage through one of the analysers. Internal and external analyser surfaces were contaminated with HIV serum, evidence that sample splashes occur during testing.

CONCLUSIONS

Due to the extreme sensitivity of these assays, contamination with minute amounts of HIV antibody can cause a negative sample to test positive. Better contamination control measures are needed on analysers used in clinical pathology environments, especially in regions where HIV sero-prevalence is high.

Development of Monoclonal Antibodies against HIV-1 p24 Protein and Its Application in Colloidal Gold Immunochromatographic Assay for HIV-1 Detection

Human immunodeficiency virus type 1 (HIV-1) p24 protein is the most abundant viral protein of HIV-1. This protein is secreted in blood serum at high levels during the early stages of HIV-1 infection, making it a biomarker for early diagnosis. In this study, a colloidal gold immunochromatographic assay (GICA) was established for detecting p24 protein using mouse monoclonal antibodies (mAbs). The HIV-1 p24 protein was expressed in E. coli strain BL21 and the purified protein was used to immunize mice. Stable hybridoma cell lines secreting anti-p24 monoclonal antibodies were obtained after ELISA screening and subcloning by limiting dilution. 34 different capture and labeling mAb pairs were selected by a novel antibody-capture indirect sandwich ELISA and then applied in GICA to detect p24 protein. The GICA method has a limit of detection (LOD) of 25 pg/mL and could detect p24 protein in all 10 positive samples obtained from the National Reference of HIV-1 p24 antigen. Out of 153 negative samples tested, 3 false positives results were obtained. The overall specificity of this test was 98.03%. The good sensitivity and specificity of this method make it a suitable alternative to provide a more convenient and efficient tool for early diagnosis of HIV infection.

Co-infections and transmission networks of HCV, HIV-1 and HPgV among people who inject drugs

Co-infections with human immunodeficiency virus type 1 (HIV-1) and human pegivirus (HPgV) are common in hepatitis C virus (HCV)-infected individuals. However, analysis on the evolutionary dynamics and transmission network profiles of these viruses among individuals with multiple infections remains limited. A total of 228 injecting drug users (IDUs), either HCV- and/or HIV-1-infected, were recruited in Kuala Lumpur, Malaysia. HCV, HIV-1 and HPgV genes were sequenced, with epidemic growth rates assessed by the Bayesian coalescent method. Based on the sequence data, mono-, dual- and triple-infection were detected in 38.8%, 40.6% and 20.6% of the subjects, respectively. Fifteen transmission networks involving HCV (subtype 1a, 1b, 3a and 3b), HIV-1 (CRF33_01B) and HPgV (genotype 2) were identified and characterized. Genealogical estimates indicated that the predominant HCV, HIV-1 and HPgV genotypes were introduced into the IDUs population through multiple sub-epidemics that emerged as early as 1950s (HCV), 1980s (HIV-1) and 1990s (HPgV). By determining the difference in divergence times between viral lineages (ΔtMRCA), we also showed that the frequency of viral co-transmission is low among these IDUs. Despite increased access to therapy and other harm reduction interventions, the continuous emergence and coexistence of new transmission networks suggest persistent multiple viral transmissions among IDUs.

Using Elecsys® HIV Combi PT assay to identify acute and early HIV infection in a teaching hospital of southwest China

This study is the first attempt to evaluate the use of the Elecsys® HIV combi PT assay in identifying acute and early HIV infection in southwest China. We also analyzed the extent of cutoff ratios overlap between false-positive and true-positive results to aid the identification of HIV infection, using samples from the West China Hospital in Chengdu, Sichuan Province from April 2012 to December 2013. Reactive results from a screening test were retested and all repeatedly reactive samples - if available - were confirmed with Western blot, HIV-1 p24 antigen, or HIV-1 RNA. Of 241,840 samples screened, the Elecsys® HIV combi PT assay identified 54 patients with acute and early HIV infection; 99.8% cases with cutoff index ratios ≥50 were proved to be true-positive HIV infection and 95.6% cases with cutoff index ratios <15 were falsely positive. In conclusion, the Elecsys® HIV combi PT assay can identify acute and early HIV infection, including those who might have been missed by third-generation HIV screening assays and Western blot. However, cutoff index ratios <15 are not always false-reactive results; a definitive result cannot be attained without further confirmation. In resource-poor regions where a HIV-1 nucleic acid test may be unaffordable, detection of HIV-1 p24 antigen can be an alternative strategy to diagnose HIV infection in individuals with a negative or indeterminate Western blot.

Performances of fourth generation HIV antigen/antibody assays on filter paper for detection of early HIV infections

BACKGROUND

Point-of-care testing and diagnosis of HIV acute infections play important roles in preventing transmission, but HIV rapid diagnosis tests have poor capacity to detect early infections. Filter paper can be used for capillary blood collection and HIV testing using 4th generation immunoassays.

OBJECTIVES

Antigen/antibody combined immunoassays were evaluated for their capacity to identify early HIV infections using filter paper in comparison with rapid test.

STUDY DESIGN

Thirty nine serum samples collected from HIV seroconverters were spotted onto filter paper and tested by the Roche Elecsys(®) HIV Combi PT test and the DiaSorin Liaison XL Murex HIV Ab/Ag assay.

RESULTS

Fourth generation immunoassays identified 34 out of 39 HIV early infections using dried serum spot, whereas the Determine™ HIV-1/2 rapid test detected 24 out of 39 HIV positive serum (87.2% vs 61.5% respectively, p = 0.009). p24 antigen was detected by the Liaison XL in 19 dried serum samples (48.7%). In the group characterized by a negative western blot, 7 out of 8 (87.5%) and 6 out of 8 (75.0%) samples were found positive for HIV using the Elecsys and the Liaison XL, respectively. None of these eight samples classified in this group of early acute infections were found positive by the rapid test.

CONCLUSION

Fourth generation Ag/Ab immunoassays performed on dried serum spot had good performance for HIV testing during the early phases of HIV infection. This method may be useful to detect HIV early infections in hard-to-reach populations and individuals living in remote areas before rapid tests become positive.

Generation of a recombinant Gag virus-like-particle panel for the evaluation of p24 antigen detection by diagnostic HIV tests

Background

Detection of HIV-1 p24 antigen permits early identification of primary HIV infection and timely intervention to limit further spread of the infection. Principally, HIV screening should equally detect all viral variants, but reagents for a standardised test evaluation are limited. Therefore, we aimed to create an inexhaustible panel of diverse HIV-1 p24 antigens.

Methods

We generated a panel of 43 recombinantly expressed virus-like particles (VLPs), containing the structural Gag proteins of HIV-1 subtypes A-H and circulating recombinant forms (CRF) CRF01_AE, CRF02_AG, CRF12_BF, CRF20_BG and group O. Eleven 4^th generation antigen/antibody tests and five antigen-only tests were evaluated for their ability to detect VLPs diluted in human plasma to p24 concentrations equivalent to 50, 10 and 2 IU/ml of the WHO p24 standard. Three tests were also evaluated for their ability to detect p24 after heat-denaturation for immune-complex disruption, a pre-requisite for ultrasensitive p24 detection.

Results

Our VLP panel exhibited an average intra-clade p24 diversity of 6.7%. Among the 4^th generation tests, the Abbott Architect and Siemens Enzygnost Integral 4 had the highest sensitivity of 97.7% and 93%, respectively. Alere Determine Combo and BioRad Access were least sensitive with 10.1% and 40.3%, respectively. Antigen-only tests were slightly more sensitive than combination tests. Almost all tests detected the WHO HIV-1 p24 standard at a concentration of 2 IU/ml, but their ability to detect this input for different subtypes varied greatly. Heat-treatment lowered overall detectability of HIV-1 p24 in two of the three tests, but only few VLPs had a more than 3-fold loss in p24 detection.

Conclusions

The HIV-1 Gag subtype panel has a broad diversity and proved useful for a standardised evaluation of the detection limit and breadth of subtype detection of p24 antigen-detecting tests. Several tests exhibited problems, particularly with non-B subtypes.

Point-of-care diagnostics, a major opportunity for change in traditional diagnostic approaches: potential and limitations

'Point-of-care' (POC) diagnostics are a powerful emerging healthcare approach. They can rapidly provide statistically significant results, are simple to use, do not require specialized equipment and are cost-effective. For these reasons, they have the potential to play a major role in revolutionizing the diagnosis, initiation and monitoring of treatment of major global diseases. This review focuses on antibody-based POC devices that target four major global diseases: cardiovascular diseases, prostate cancer, HIV infection and tuberculosis. The key statistics and pathology of each disease is described in detail, followed by an in-depth discussion on emerging POC devices that target each disease, highlighting their potential and limitations.