Evaluation of the Abbott Alinity S and the Roche Cobas e801 for Virology screening at the South African National Blood Service Charl Coleman, Jabu Jaza, Solly Machaba, Marion Vermeulen South African National Blood Service
Introduction • SANBS test all donations for Human Immunodeficiency Virus (HIV), Hepatitis C (HCV) and Hepatitis B (HBV) • Nucleic Acid Testing (NAT) and Viral Serology Testing (anti-HIV, anti-HCV and HBV Surface Antigen (HBsAg) are performed • Viral Serology was performed on the Abbott Prism for the past 15 years at SANBS
Introduction • Aim to evaluate two new viral serology systems Abbott Alinity S (Alinity) Roche Cobas e801 (Cobas) • A third system namely the Siemens Atellica was also part of the original evaluation plan, but the system installation was not successful and in time for evaluation
Background • Cobas assays HIV Duo (5 th gen), HBsAg and anti-HCV • Alinity assays Alinity HIV Ag/Ab (4 th gen), HBsAg and anti-HCV • The HIV assays for Cobas and Alinity are both able to detect HIV antigen and antibody compared to the previous Abbott Prism assay used that were antibody only detection • The detection of antigen is not an added benefit for SANBS, because of NAT testing • SANBS do perform the p24 antigen test though on all NAT reactive, anti-HIV negative donors in order to provide detail regarding the window period stage and also to compare data to pre- NAT screening data when p24 antigen testing was performed on all donors
Methods • Specificity was determined by testing approximately 200-300 first time donor specimens from Johannesburg and Durban Donation Testing laboratories (December 2017 and May 2018) • All discordant reactive samples were confirmed using the NAT result (Procleix ULTRIO Elite) or confirmatory testing for anti-HIV (Biorad Geenius), HBsAg (Roche e411 neutralization) or anti-HCV (Roche e411 HCV and Innogenetics HCV INNO LIA Score) • Specificity was determined (HIV N=3953, HCV N=3899 and HBsAg N=3953) as per calculation True Negatives (TN) / (False Positives + TN) x 100 • Sensitivity was evaluated by comparing confirmed positive plasma (NAT Reactive, anti-HIV reactive) and a panel of HIV NAT yields (p24 positive and p24 negative) • The Chi-squared test was used to test for statistical significance • The coefficient of variation (%CV) was calculated from inter (x30) - and intra-run repeats (10x across 3 runs) of custom quality controls. Instrument failures were recorded • The total uptime of each instrument was recorded as well time spend on maintenance. The analyzer maintenance uptime ratio was calculated as the % Total maintenance time/Total uptime
Methods Specificity Sensitivity Variability Plasma Donor samples Plasma Inter-run comparison Intra-run comparison 20x HIV NAT Yield, p24 (HIV N=3953, HCV N=3899 and 20x HIV NAT Yield, p24 3 x runs of 10 per 30x HIV, HBsAg and antigen negative HBsAg N=3953) antigen positive marker HCV (VL>1000 cp/ML) Plasma Plasma 15X HIV Confirmed 15X HIV Confirmed positives (NAT Reactive, positives (NAT Reactive, anti-HIV reactive) Prism anti-HIV reactive) Prism Instrument reliability S/CO <20 S/CO >20 (MTBF) Plasma Plasma 15X HBsAg Confirmed 15X HBsAg Confirmed positive S/CO ratio >20 positive S/CO ratio <20 Plasma 13X Anti-HCV Confirmed positive • The intra assay variation - variation of results within a data set obtained from one run • The inter assay - variation of results obtained from repeated runs (x3) • Coefficient of variation (%CV) = Standard deviation of observation/Mean
Results Specificity of the assays on the Cobas e801 vs the Abbott Alinity S 99.97% 99.95% 99.95% 99.90% 99.90% 99.77% HIV HBsAg HCV Cobas Alinity • Although there were differences in specificities, it was found to be statistically insignificant (HIV p=0.57, HBsAg p=0.49 and HCV p=0.17) • The biggest difference in specificity on HCV • The overall difference in specificity between the systems were 0.15% in favor of Alinity
Results • Sensitivity on donors samples (HIV N=3953, HCV N=3899 and HBsAg N=3953) were 100% for both Cobas and Alinity • Sensitivity determined by p24 antigen positive confirmed NAT yield samples was 95% (19/20) on both Cobas and Alinity • The sample not detected by both had a viral load of 37,537 copies per mL with a p24 antigen positive result S/Co ratio of 1.56 • Sensitivity determined by p24 antigen negative HIV confirmed NAT yields was 4/19 (21%) on Cobas and 5/19 (26%) on Alinity (4/5 positive by both systems and one detected by Alinity only)
Results • Total uptime on Cobas during evaluation was 432 hours compared to 310 hours for Alinity • No failures occurred on Cobas whereas one failure (not leading to downtime) occurred on Alinity therefore MTBF could not be calculated • Analyser maintenance time ratio was calculated as 8.9% for Cobas compared to 10.4% for Alinity • The Alinity took approximately 30 – 40 min per day (preparation and instrument maintenance running time) whereas the Cobas required 23 minutes daily (no preparation, only instrument maintenance running time)
Results Coefficient of Variation (%CV) achieved in inter- and intra-run comparisons for Cobas and Alinity 6.71% Alinity 3.10% Cobas • A %CV of less than 10% is desirable • Cobas S/CO ratios obtained through repeat sampling are narrower than that obtained from Alinity
Discussion • The Abbott Alinity S was selected by SANBS mainly due to specificity criteria, which was the most important aspect of the evaluation • Specificity has a direct impact on the number of available units for transfusion and the amount of confirmatory work required • The largest specificity difference was on anti-HCV. The total difference in specificity across all markers of 0.15% in favor of Alinity was considered • With a collection target of 900,000 units per annum, 1350 less donors would be deferred and the loss of units valued at R2, 521,800 per annum would be avoided • The sensitivity and reproducibility criteria was met by both Cobas and Alinity. Both system showed robustness with little downtime occurring
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