title: Factor Xa-activated whole blood clotting time (Xa-ACT) for bedside monitoring of dalteparin anticoagulation during haemodialysis.
abstract: BACKGROUND
  Low molecular weight heparins (LMWH) like dalteparin are increasingly used for anticoagulation during haemodialysis (HD). The available laboratory tests for monitoring LMWH anticoagulation are time-consuming and expensive, and the suitability of the conventional activated clotting time (ACT) is controversial. A simple and cheap bedside test would be useful.
  
  
  METHODS
  We studied the factor Xa-activated whole blood clotting time (Xa-ACT) in vitro and in vivo in nine patients undergoing chronic HD with i.v. dalteparin bolus anticoagulation and compared it with the conventional ACT. Plasma anti-factor Xa (antiXa) activity was determined with a chromogenic assay. Thrombin-antithrombin complexes were measured to detect coagulation activation.
  
  
  RESULTS
  Xa-ACT and ACT were prolonged with rising dalteparin concentration. In vitro, both clotting times were strongly correlated with the antiXa levels (r = 0.94 and 0.89, respectively). Nevertheless, compared with the ACT, the Xa-ACT was considerably more sensitive to the LMWH in vitro (healthy blood: Xa-ACT 90 s/U vs ACT 26 s/U; uraemic blood: Xa-ACT 96 s/U vs ACT 31 s/U) as well as in vivo (Xa-ACT 81 s/U vs ACT 22 s/U) and reflected different intensities of anticoagulation. An initial dalteparin bolus of 80+/-11 U/kg body weight was able to prevent coagulation activation for up to 4 h of HD.
  
  
  CONCLUSIONS
  For monitoring LMWH anticoagulation the Xa-ACT was superior to the conventional ACT in vitro as well as in vivo during HD. The Xa-ACT can be useful as a LMWH bedside test. The ACT was not sensitive enough to serve as a LMWH monitoring tool.
authors.affiliation: Department of Nephrology and Clinical Immunlogy, University Hospital Aachen, D-52057 Aachen, Germany. dario.frank@ukaachen.de
authors.forename: Rolf Dario
authors.initials: RD
authors.lastname: Frank
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Brandenburg
authors.forename: Regina
authors.initials: R
authors.lastname: Lanzmich
authors.forename: Jürgen
authors.initials: J
authors.lastname: Floege
mesh_terms: D000328:Adult; D000368:Aged; D000925:Anticoagulants / Q000009:adverse effects / Q000627:therapeutic use*; D017985:Dalteparin / Q000008:administration & dosage / Q000627:therapeutic use*; D015951:Factor Xa; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D019095:Point-of-Care Systems; D006435:Renal Dialysis; D014914:Whole Blood Coagulation Time
chemical_list: D000925:Anticoagulants; D015951:Factor Xa; D017985:Dalteparin