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Poor standardization of preanalytic variables exerts a strong influence on the reliability of coagulation testing, consuming valuable health care resources and compromising patient outcome. Most uncertainties emerge from patient misidentification and the procedures for specimen collection and handling. Location of unsuitable venous access or problematic phlebotomies may produce spurious activation of the hemostatic system and hemolytic specimens. Prolonged venous stasis is associated with hemoconcentration and spurious variations of most coagulation assays. Additional pitfalls can be introduced by inappropriate phlebotomy tools and small-gauge needles. Inappropriate filling and mixing of the tube, unsuitable procedures for centrifugation and storage of the specimens are additional aspects that need accurate standardization. Besides traditional preanalytic variables affecting routine coagulation testing, thrombin-generation assays require specific criteria to be accurately fulfilled. These aspects include the type of specimen (platelet-poor plasma, platelet-rich plasma or whole blood), blood collection tubes, storage conditions and the presence of residual platelets. Compliance with new international quality assessment programs, which will also involve coagulation laboratories, encompasses the adoption of suitable strategies for reducing undue variability throughout the whole testing process. Such strategies would not entail extraordinary costs and are affordable with a structured outlay of existing resources, educational policies and compliance with reliable guidelines.