Association between standard laboratory and functional tests of coagulation in dilutional coagulopathy: an in vitro study.

Standard laboratory tests (SLTs) of coagulation are in common use in clinical practice. We aimed to determine the association between SLTs and functional tests of coagulation in blood samples diluted with balanced crystalloid and colloid solutions in an ex vivo setting. The study group comprised 32 healthy young male volunteers. Whole blood samples were diluted at a 4:1 ratio with balanced crystalloid (Plasmalyte®) and two balanced colloids, 6% hydroxyethyl starch 130/0.4 (Volulyte®) and succinylated gelatin (Geloplasma®). SLTs included aPTT (activated partial thromboplastin time), PT (prothrombin time), fibrinogen concentration (FIB), D-dimers and number of platelets (PLT). Platelet aggregation was determined using multiple electrode aggregometry (MEA) with TRAP (thrombin receptor activating protein-6) as an assay activator. Coagulation and fibrinolysis were assessed functionally using rotational thromboelastometry (ROTEM). We found correlation between aPTT and INTEM (i.e. intrinsic coagulation pathway screening test) clotting time (R = 0.38 to 0.77; P < 0.05) for both undiluted and diluted samples. FIB and PLT were shown to be correlated with alpha angle in both INTEM and EXTEM (i.e. extrinsic coagulation pathway screening test) (FIB: R = 0.38 to 0.69; P < 0.05; PLT: 0.41 to 0.56; P < 0.05) again for both undiluted and diluted samples. FIB and PLT were associated with clot formation time in both INTEM and EXTEM (FIB: R = -0.44 to -0.70; P < 0.05; PLT: -0.36 to -0.58; P < 0.05). MEA results shown no correlation with ROTEM findings. There was also no correlation between number of platelets and their function as determined by MEA. Fibrinogen concentration correlated positively with fibrinogen function as determined by FIBTEM (i.e. fibrinogen deficiency/dysfunction screening test) maximum clot firmness (R = 0.49 to 0.73; P < 0.05). ROTEM results were predominantly associated with fibrinogen concentration and number of platelets. When there is no access to functional tests, concentration of fibrinogen is the most reliable test of coagulation, also in the context of fluid-induced coagulopathy.