PB1121 - Laboratory INRs determined with commercial thromboplastins in >450 centres before and after the establishment of the IRP for human thromboplastin - rTF 16 : Data from UK NEQAS for Blood Coagulation

Background: Vitamin K antagonist therapy (VKA) should be monitored by International Normalised Ratio (INR). The current International Reference Preparation for human thromboplastin coded rTF 16 replaced human IRP coded rTF 09. In the calibration exercise rTF 16 was calibrated against rTF 09 and RBT 05. The ISI for rTF 16 against rTF 09 was 1.09 and against RBT 05 was 1.14. After implementing the WHO requirement to use the mean of ISIs against both, an ISI value 1.11 was assigned to rTF 16.

Aims: To check the impact of changeover from rTF 09 to rTF 16 on INRs determined with commercial thromboplastins .

Methods: A sample with a high INR was prepared from subjects on VKA therapy was analysed in >450 centres in 2018 and again in 2022 using local analyser/thromboplastins. Manufacturers were contacted to confirm whether thromboplastins were traceable to rTF 09 or rTF 16.

Results: In 2018 >80% of tests were performed with reagents traceable to rTF 09. In 2022 > 55% of tests were performed with reagents traceable to rTF16. Results are shown in Table 1. INRs determined with Recombiplastin 2G in 2022 were 4.3% higher than in 2018 – before and after a full changeover in traceability . Approximately 45% of centres using Innovin who gave lot numbers had changed over to rTF 16 traceability by 2022 with 1.1% difference in INRs. Traceability of Stago Neoplastin R was to rTF 16 in both surveys.

Conclusion(s): Changeover in traceability was associated with small and clinically irrelevant differences in median INRs with 2 widely used thromboplastins. The overall median INR obtained by >450 centres using a total of 13 different thromboplastins was 2.6% higher in 2022 than in 2018. This difference would not have any adverse effects on management of patients undertaking VKA therapy .