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

Roche Cobas e801 (Cobas) Abbott Alinity S (Alinity)

• 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 (5th gen), HBsAg and anti-HCV

• Alinity assays Alinity HIV Ag/Ab (4th 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

• 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

Donor samples (HIV N=3953, HCV N=3899 and

HBsAg N=3953)

Specificity Sensitivity

Plasma20x HIV NAT Yield, p24

antigen positive

Plasma20x HIV NAT Yield, p24

antigen negative (VL>1000 cp/ML)

Variability

Inter-run comparison3 x runs of 10 per

marker

Intra-run comparison30x HIV, HBsAg and

HCV

Instrument reliability(MTBF)

Plasma15X HIV Confirmed

positives (NAT Reactive, anti-HIV reactive) Prism

S/CO <20

Plasma15X HIV Confirmed

positives (NAT Reactive, anti-HIV reactive) Prism

S/CO >20

Plasma15X HBsAg Confirmed

positive S/CO ratio >20

Plasma15X HBsAg Confirmed

positive S/CO ratio <20

Plasma13X Anti-HCV

Confirmed positive

Results

• 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

HIV HBsAg HCV

99.95% 99.95%

99.77%

99.97%

99.90%99.90%

Specificity of the assays on the Cobas e801 vs the Abbott Alinity S

Cobas 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

• A %CV of less than 10% is desirable• Cobas S/CO ratios obtained through repeat sampling are narrower than that obtained from Alinity

Cobas

Alinity

3.10%

6.71%

Coefficient of Variation (%CV) achieved in inter- and intra-run comparisons for Cobas and 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

Thank you…