Comparison of the Aptima HIV-1 Quant Dx assay with the COBAS AmpliPrep/COBAS TaqMan HIV-1 v2.0 Test for HIV-1 viral load quantification in plasma samples from HIV-1-infected patients

Performance Evaluation of the Aptima Assays in Comparison with the cobas 6800 Assays for the Detection of HIV-1, HBV, and HCV in Clinical Samples

Background

Accurate and consistent viral load (VL) quantitation of HIV type 1 (HIV-1), hepatitis B virus (HBV), and hepatitis C virus (HCV) is important for diagnosis and clinical monitoring. Assay results have to be concordant and compatible across laboratories. We evaluated the performance of three Aptima assays (Hologic, San Diego, CA, USA) and compared their VL values with corresponding cobas 6800 assay (Roche Diagnostics, Mannheim, Germany) results, using 840 clinical samples.

Methods

The correlation between VL results obtained using the two assays was evaluated in terms of analytical sensitivity, precision/reproducibility, linearity, and cross-reactivity. Agreement rates were determined using kappa statistics. The overall agreement of VL values was examined using Passing–Bablok regression analysis.

Results

All CVs were within 5%; the assays had good precision for detecting all three viruses. The linearity of quantitation assessed using three AccuSpan linearity panels (Seracare, Milford, MA, USA), was excellent for the Aptima assays. For HIV-1 and HCV, the results of both assays showed excellent agreement (κ=0.89 and 0.90, respectively) while for HBV, the results showed good agreement (κ=0.69). For analytical sensitivity, the VLs required for a 100% detection rate of HIV-1, HBV, and HCV were 20 copies/mL, 7.5 IU/mL, and 5.0 IU/mL, respectively. The results for HIV-1, HBV, and HCV obtained using both assays correlated strongly (R²=0.97, 0.93, and 0.95, respectively).

Conclusions

The cobas 6800 and Aptima assays, with fully automated and high-throughput molecular platforms for HIV-1, HBV, and HCV VL measurements, show good analytical performance and a strong correlation between results. The study results suggest that the assays can be used interchangeably for long-term monitoring of chronic infections.

Study To Evaluate the Performance of a Point-of-Care Whole-Blood HIV Viral Load Test (SAMBA II HIV-1 Semi-Q Whole Blood)

Remote areas of many low and middle income (LMI) countries have poor access to HIV viral load (HIV VL) testing. The SAMBA II (simple amplification-based assay) Semi-Q whole-blood test (Diagnostics for the Real World [DRW], Cambridge, UK) is a point-of-care assay, which uses leucodepletion technology to allow whole-blood testing in remote settings. A total of 1,540 consecutive HIV-positive clinic patients in Cameroon (250), United Kingdom (633), Ukraine (412), and Zimbabwe (245) donated venous blood (all countries) and finger prick blood (all except UK) for testing on SAMBA II. SAMBA II results were compared with simultaneous plasma results on the Abbott RealTime HIV-1 (Abbott Molecular, Des Plaines, IL) viral load assay and interpreted as either <1,000 RNA copies/ml or ≥1,000 RNA copies/ml. For 1,528 venous whole-blood samples tested on SAMBA II, overall percent agreement with the reference test at a cutoff HIV VL of ≥1,000 copies/ml was 96.9% (1,480/1,528; 95% confidence interval [CI], 95.9% to 97.7%), negative percent agreement was 97.7% (1,259/1,289; 95% CI, 96.7% to 98.4%), and positive percent agreement was 92.5% (221/239; 95% CI, 88.4% to 95.5%). For 854 finger prick samples, there was 95.0% (811/854; 95% CI, 93.3% to 96.3%) overall percent agreement, 98.0% (625/638; 95% CI, 96.5% to 98.9%) negative percent agreement, and 86.1% (186/216; 95% CI, 80.8% to 90.4%) positive percent agreement. These rose to 93.5% (82.1% to 98.6%), 97.6% (95.6% to 98.8%), and 95.6% (93.3% to 97.3%) after exclusion of aberrant results from the Ukraine center. These results show a high level of agreement between SAMBA-II and a laboratory-based assay. SAMBA-II has a performance that is suitable to use as a VL point-of-care assay in remote settings.

The Development of a Standardized Quality Assessment Material to Support Xpert® HIV-1 Viral Load Testing for ART Monitoring in South Africa

The tiered laboratory framework for human immunodeficiency virus (HIV) viral load monitoring accommodates a range of HIV viral load testing platforms, with quality assessment critical to ensure quality patient testing. HIV plasma viral load testing is challenged by the instability of viral RNA. An approach using an RNA stabilizing buffer is described for the Xpert^® HIV-1 Viral Load (Cepheid) assay and was tested in remote laboratories in South Africa. Plasma panels with known HIV viral titres were prepared in PrimeStore molecular transport medium for per-module verification and per-instrument external quality assessment. The panels were transported at ambient temperatures to 13 testing laboratories during 2017 and 2018, tested according to standard procedures and uploaded to a web portal for analysis. A total of 275 quality assessment specimens (57 verification panels and two EQA cycles) were tested. All participating laboratories met study verification criteria (n = 171 specimens) with an overall concordance correlation coefficient (ρ_c) of 0.997 (95% confidence interval (CI): 0.996 to 0.998) and a mean bias of −0.019 log copies per milliliter (cp/mL) (95% CI: −0.044 to 0.063). The overall EQA ρ_c (n = 104 specimens) was 0.999 (95% CI: 0.998 to 0.999), with a mean bias of 0.03 log cp/mL (95% CI: 0.02 to 0.05). These panels are suitable for use in quality monitoring of Xpert^® HIV-1 VL and are applicable to laboratories in remote settings.

Performance evaluation of the Aptima HIV-1 RNA Quant assay on the Panther system using the standard and dilution protocols

BACKGROUND

Currently, FDA-approved HIV-1 viral load (VL) assays use venipuncture-derived plasma. The Hologic Panther system uses 0.7 mL total volume for the Aptima HIV-1 Quant Assay standard (APT-Quant-std) and dilution (APT-Quant-dil) protocols. However, smaller plasma volumes from fingerstick whole blood (FSB) collected in EDTA-microtainer tubes (MCT) could provide an easier sample collection method for HIV-1 VL testing.

OBJECTIVES

To evaluate the performance of the APT-Quant-std compared to the Roche CAP/CTM and Abbott m2000RT VL assays and an alternative APTQuant 1:7 dilution protocol, the latter using 100 μL of MCT-derived plasma from FSB.

STUDY DESIGN

Linearity was determined using commercial HIV-1 RNA plasma controls. Dilutions ranging 1.56-2.95 log10 copies/mL were prepared to determine the APT-Quant-dil Limit of Quantitation (LOQ) using Probit analysis. Specificity of APT-Quant-std was calculated using 326 HIVnegative samples. To evaluate agreement, 329 plasma specimens were tested with APT-Quant-std, CAP/CTM, and m2000RT. Forty-seven matched venipuncture and MCT-derived plasma specimens were tested with APT-Quant-std and APT-Quant-dil.

RESULTS

Among the RNA controls, specificity was 99.69 % for APT-Quant-std. The R2 values were 0.988 (APT-Quant-std/CAP/CTM), 0.980 (APT-Quant-std/ m2000RT), and 0.997 (APT-Quant-std/APT-Quant-dil). The APT-Quant-dil LOQ was estimated at 2.7 log10 copies/mL (500 copies/mL) (95 %CI 2.62-2.87). At 2.3 log10 copies/mL (200 copies/mL), the overall agreement was 91.0 % for APT-Quant-std/CAP/CTM, 85.7 % for APT-Quant-std/m2000RT, and 82.9 % for APT-Quant-std/APT-Quant-dil. Quantified APT-Quant-std results were on average 0.2 log10 copies/mL higher than CAP/CTM and m2000RT and 0.14 log10 copies/mL higher than APT-Quant-dil.

CONCLUSION

APT-Quant showed similar performance compared to the CAP/CTM and m2000RT assays and remains sensitive and accurate using the dilution protocol.

Could HIV-1 RNA Testing be an Option as the Second Step in the HIV Diagnostic Algorithm?

BACKGROUND

There is benefit to early HIV-1 diagnosis and treatment, but there is no Food and Drug Administration-approved quantitative assay with a diagnostic claim. We compared the performance of the Hologic Aptima HIV-1 Quant (APT-Quant) and Aptima HIV-1 Qual (APT-Qual) assays for diagnostic use and the performance of a diagnostic algorithm consisting of Bio-Rad BioPlex 2200 HIV Ag-Ab assay (BPC) followed by APT-Quant (2-test) compared with BPC followed by Geenius HIV-1/2 supplemental assay (Geenius) with reflex to APT-Qual (3-test).

METHODS

Five hundred twenty-four plasma, which included 419 longitudinal specimens from HIV-1 seroconverters (78 were after initiating antiretroviral therapy [ART]) and 105 from ART-naive persons with established HIV-1 infections, were used to evaluate APT-Quant performance for diagnostic use. Specimens from 200 HIV-negative persons were used to measure specificity. For the algorithm comparison, BPC-reactive specimens were evaluated with the 2-test or 3-test algorithm. McNemar's test was used to compare performance.

RESULTS

The APT-Quant detected more samples early in infection compared with APT-Qual. The APT-Quant specificity was 99.8%. Before ART initiation, the algorithms performed similarly among samples from different stages of infection. After ART initiation, the 3-test algorithm performed significantly better (P = 0.0233).

CONCLUSIONS

The APT-Quant has excellent performance for diagnostic use. The 2-test algorithm works well in ART-naive samples, but its performance decreases after the IgG response is elicited and with ART-induced suppressed viremia. Providing confirmation and viral load assay with 1 test result could be advantageous for patient care. However, additional factors and challenges associated with the implementation of this 2-test algorithm, such as cost, specimen type, and collection need further evaluation.