COAGULATION
stage will be to introduce a broader range of assays for specialist laboratories, with 28 parameters available in early 2024.
One study now underway in the UK is taking place at the Oxford Haemophilia and Thrombosis Centre (OHTC), part of Oxford University Hospitals’ NHS Foundation Trust. Ahead of the results being published, lead scientist Peter Baker indicated: “It’s certainly fast – and very quick to the first result being produced.” His preliminary findings show its comparability to current instruments and are expected to be in line with those of the already published study by Pontis et al.1
Four minutes to first result “The high-throughput sthemO takes just four minutes on average to first result, making it one of the fastest instruments on the market,” Mr Querel added. Stago Global marketing first met with the Oxford team during ISTH 2022. This led to Stago inviting Oxford to test out an early look model, even ahead of it being finalised.
“The Oxford team has been instrumental in testing out not only the assays but the functionality of the new instrument in a real-time setting; working with Stago’s global team and providing feedback on the fine tuning we were making,” he explained. “OHTC has worked with Stago in the past and we value its direct and approachable attitude to innovation.”
Excellent assay correlation Pontis et al1
highlighted the ‘consistency’
and ‘very high’ precision obtained with the sthemO 301 system, showing almost 100% correlation with Stago’s existing
Viscosity-based detection system lies at the heart of all Stago analysers, mechanically detecting when the clot forms using electromagnetic fields to measure increases in the viscosity of the sample plasma
STA R Max 2 platform. Overall agreement between the two systems was excellent for all assays, with Spearman rank correlation coefficient all above 0.9 and slopes of Passing–Bablok correlation near 1 and intercepts close to 0. The Spearman rank correlation coefficient was also used to further evaluate the strength and direction of the correlation. Inter-assay coefficients of variation (CVs) ranged from 1.5% to 5.5%, which is consistently lower than the limits set as officially acceptable by France’s leading organisation for professional practice in haemostasis and thrombosis. (Diagnostica Stago is a member of the French Society of Haematology, of which the GFHT is a study group publishing recommendations and acceptance criteria to help laboratories during the verification process.)
The study included comparison of clotting (chronometric), chromogenic and immunological methods using sthemO 301 analyser-dedicated reagents, calibrators and controls. This evaluation supported the results obtained with Stago’s external quality assessment (EQA) samples, which confirmed the accuracy of the routine PT, APTT, TT, Fib, PC clotting, PC chromogenic, and VWF:Ag assays undertaken on the sthemO 301.
Detecting HIL interferences Insensitivity to HIL is a major benefit of Stago instrumentation. VBDS lies at the heart of all Stago analysers, with more than 450 million tests worldwide now performed using it. It mechanically detects when the clot forms using electromagnetic fields to measure increases in the viscosity of the sample plasma. All other systems on the UK market rely on a change in optical density to detect this. Yannig Querel explains: “Until there is published evidence to the contrary, the CLSI guidelines2
advise that mechanical
or electromechanical methods for clot detection should always be incorporated. Our VBDS system delivers this, removing any such HIL issues. Concern over being able to reliably measure some HIL samples using optical methods alone can cause inconvenience for the patient and the additional cost of having to rebleed them.”
Pontis indicates that the detection of HIL was comparable between analysers. This was carried out by checking the consistency of levels provided by the Expert Preanalytical Check (EPC) modules on both sthemO 301 and STA R Max 2, compared to a visual check by the operator. A study,3
carried out by Steve Kitchen Lipaemia Haemolysis Icterus
and Anita Woolley (Royal Hallamshire Hospital, Sheffield Haemophilia and Thrombosis Centre), had previously confirmed the accuracy of three routine Stago coagulation assays, PT, APTT and fibrinogen when investigating potential interferences. It noted that Stago systems with VBDS, running the company’s routine reagents, showed on average no clinically relevant bias with coloured or turbid plasma as a result of HIL.
350 400 450 500 Wavelength (nm)
Fig 2. A spectrograph showing the wavelengths at which haemolysis, icterus and lipaemia may cause interference.
WWW.PATHOLOGYINPRACTICE.COM SEPTEMBER 2023 550 600 650
High assay precision The Pontis study also observed that there was no statistically significant inter-sample carryover (all P>0.05), except two instances when a nominal difference of ±0.3 second was noted. This was observed when looking at PT from normal to abnormal in seconds only (P=0.02), with the abnormal PT moving from 34.5 to 34.8 seconds. The
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