Nonanalytical Variables Affecting the Laboratory Evaluation of Hemostasis

Nonanalytical Variables Affecting the Laboratory Evaluation of Hemostasis 

Many of the coagulation factors measured by global coagulation tests have limited stability, and the time and temperature of storage of sample will affect their measurements. Concepts of analyte stability and half-life in plasma extend to markers measured by immunoassay. Markers of platelet activation are affected by artifactual activation in vitro upon collection of the blood specimen. This section will highlight some of the nonanalytical variables that, if uncontrolled, can lead to spurious results and thus affect the interpretation of laboratory data. 

Preanalytical Variables Affecting Global Coagulation Tests 

Preanalytical variables that affect global tests for coagulation such as prothrombin time (PT) and activated partial thromboplastin time (APTT) include the choice and concentration of anticoagulant, anticoagulant-to-blQod ratio, pH, concentration of divalent cations, hematocrit, and storage temperature, to mention a few. 

As to the choice of anticoagulant, citrate is preferred to oxalate, because factor V is more stable in citrate than in oxalate. In addition, citrate rapidly complexes with calcium, forming a soluble complex, in contrast to the slow formation of the insoluble complex of calcium with oxalate (100). 

---

Nonanalytical Variables Affecting the Laboratory Evaluation of Hemostasis. 157... 

---