Comparison of 2 thromboelastography methods using patient and control samples

Background: Viscoelastic testing at point-of-care is associated with reduced blood loss and blood product transfusions. The ROTEM (Werfen) sigma is a cartridge-based system that may facilitate point-of-care use, but limited studies exist comparing the sigma with the predicated ROTEM delta. Objectives: We compared the performance of the ROTEM delta with that of the sigma. Methods: Citrated blood was collected from 20 healthy donors and patients during liver transplants (n = 17), obstetrics (n = 15), cardiovascular (n = 9), and trauma surgeries (n = 10). A method comparison was performed using the delta as the predicate. Imprecision was assessed at 2 levels for each assay. Manufacturer reference intervals were verified using 20 healthy donors. An algorithm used for cardiovascular surgery with the delta was compared with the sigma. Results: The coefficient of variation was <10% for all assays/parameters except for the thromboelastometry with extrinsic activation (EXTEM) clotting time (10.3%) and EXTEM amplitude (A)5 (10.2%). Reference intervals for the delta and sigma were comparable to manufacturer claims. The Pearson r comparing the delta and sigma exceeded .85 for all parameters/assays except for thromboelastometry with cytochalasin D-mediated platelet inhibition (FIBTEM) A10 (.77; 95% CI, .66-.86), FIBTEM A20 (.78; 95% CI, .65-.87), and thromboelastometry with heparinase clotting time (.77; 95% CI, .61-.87). No difference was observed in extrapolated thresholds from the delta-guided algorithm. However, extrapolated sigma A5 parameters for EXTEM were 5 mm lower, and for FIBTEM were 1 mm lower than delta A10 parameters. Conclusion: The ROTEM delta and sigma devices had comparable performance. A negative bias was observed in the FIBTEM assay with lower extrapolated clinical decision points for a delta-guided treatment algorithm for the FIBTEM and EXTEM A5.