Loss of Factor VIII and von Willebrand Factor Activities during Cold Storage of Whole Blood Is Reversed by Rewarming

Documentation of preanalytical conditions that could result in inaccurate results and misdiagnoses of patients is important. It has recently been reported that a significant loss of factor VIII (FVIII) and von Willebrand factor (vWF) activity occurs when citrated whole blood is stored on ice. We tested the hypothesis that the cold-dependent loss of FVIII and vWF activity is due to the formation of cryoprecipitate and is reversed by rewarming the citrated whole blood before centrifugation and removal of plasma. We collected venous blood from 10 healthy subjects into 3.2% sodium citrate glass tubes. One tube was immediately centrifuged and the plasma was stored at -20 degrees C. Following storage in an ice bath (4 degrees C) for 3.5 hours, 1 tube was immediately centrifuged and processed while the second tube was placed in a 37 degrees C water bath for 5 minutes then centrifuged and processed. Subsequently, plasma samples were quickly thawed at 37 degrees C and the following tests were performed: prothrombin time (PT), partial thrombin time (aPTT), FVIII activity, vWF antigen (vWF:Ag), and vWF activity (vWF:Act). Means for each analyte from the 2 tubes stored at 4 degrees C for 3.5 hours with or without rewarming were compared to baseline tube using the Student t test. Compared to the baseline tube results, PT and aPTT showed no significant changes in either of the tubes stored at 4 degrees C for 3.5 hours. However, FVIII, vWF:Ag, and vWF:Act were significantly lower in the tubes stored at 4 degrees C for 3.5 hours, but no differences were detected between baseline and rewarmed tube results. In conclusion, prolonged storage of citrated whole blood at 4 degrees C causes a clinically significant reduction of FVIII and vWF activities. The losses are completely reversed by rewarming the tube prior to processing. This is consistent with a reversible cryoprecipitation of vWF and FVIII rather than a cold-activated enzymatic degradation.