Platelet Contribution to Clot Strength in Thromboelastometry: Count, Function, or Both?

In thromboelastometry (ROTEM) the difference in amplitude between the EXTEM and the FIBTEM is considered an index of platelet contribution to clot strength (PCS). The difference in elasticity (PCS) is rarely used. We investigated the ability of PCS and PCS in reflecting platelet count and function in 103 patients undergoing cardiac surgery, simultaneously measuring ROTEM and platelet function tests (multiple electrode aggregometry ADPtest and TRAPtest, Multiplate). PCS and PCS were tested for association with platelet count and function. The PCS showed a low (R coefficient 0.32-0.39) association with platelet count and function (ADPtest), whereas the PCS showed higher values of association (R coefficient 0.55-0.71) with the same variables. No association was found between PCS and TRAPtest. In a multivariable model, both the platelet count (R coefficient 0.60, P = 0.001) and the ADPtest (R coefficient 0.36, P = 0.001) were independently associated with the PCS. The discrimination properties of the PCS for the prediction of a low platelet count/function were very good (c-statistics 0.837). In clinical practice, the difference in elasticity between EXTEM and FIBTEM should replace the difference in amplitude.