title: Effect of haematocrit on fibrin-based clot firmness in the FIBTEM test.
abstract: BACKGROUND
  Point-of-care thromboelastometry (ROTEM(®)) can be used to assess coagulation in whole blood. In the ROTEM(®) FIBTEM test, cytochalasin D eliminates the contribution of platelets to the whole blood clot; hence, only the remaining elements, including fibrinogen/fibrin, red blood cells and factor XIII, contribute to clot strength. We investigated the relationships between FIBTEM maximum clot firmness (MCF), whole blood fibrinogen concentration and plasma fibrinogen concentration to determine the impact of haematocrit on these parameters during cardiac surgery.
  
  
  METHODS
  The relationships between FIBTEM MCF and both whole blood fibrinogen concentration and plasma fibrinogen concentration (Clauss assay) were evaluated pre-operatively and after cardiopulmonary bypass/protamine administration in haematocrit-based subgroups.
  
  
  RESULTS
  The study included 157 patients. The correlation coefficient rho between FIBTEM MCF and plasma fibrinogen concentration was 0.68 at baseline and 0.70 after protamine, while that between FIBTEM MCF and whole blood fibrinogen concentration was 0.74 at baseline and 0.72 after protamine (all P <0.001). In subgroup analyses based on haematocrit levels, pre-operative FIBTEM MCF and whole blood fibrinogen concentration were both significantly higher (P <0.05) for the lowest haematocrit subgroup, but plasma fibrinogen concentration was similar in all groups. After protamine, no significant differences were observed between the lowest haematocrit group and the other groups for any of the three parameters.
  
  
  CONCLUSIONS
  The effect of haematocrit on blood clotting is not reflected by plasma fibrinogen concentration, in contrast to FIBTEM MCF which incorporates the contribution of haematocrit to whole blood clot firmness. This effect does, however, appear to be negligible in haemodiluted patients.
authors.affiliation: Department of Anaesthesiology and Intensive Care, Salzburger Landeskliniken SALK, Salzburg, Austria. solomon.cristina@googlemail.com
authors.forename: Cristina
authors.initials: C
authors.lastname: Solomon
authors.forename: Niels
authors.initials: N
authors.lastname: Rahe-Meyer
authors.forename: Herbert
authors.initials: H
authors.lastname: Schöchl
authors.forename: Marco
authors.initials: M
authors.lastname: Ranucci
authors.forename: Klaus
authors.initials: K
authors.lastname: Görlinger
mesh_terms: D001777:Blood Coagulation; D001780:Blood Coagulation Tests / Q000295:instrumentation / Q000379:methods; D005260:Female; D005337:Fibrin / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism*; D006400:Hematocrit; D006801:Humans; D008297:Male
chemical_list: D005337:Fibrin; D005340:Fibrinogen