Determining the maximal storage time of centrifuged citrated samples for performing add-on routine coagulation tests

Background: Several routine coagulation tests have been developed to give insight in the coagulation pathway. The laboratory diagnostical process consists of 3 phases, the pre-analytical, analytical and post-analytical phase; however, the pre-analytical phase is most sensitive to errors. The amount of time blood is stored, can affect the measurements of these coagulation tests and result in an incorrect conclusion. Therefore, we performed experiments to determine the maximal storage time, centrifuged blood samples can be reliably measured. Methods: Citrated whole blood from hospital patients, who were tested for routine coagulation, was collected in mL citrate tubes. These whole blood samples were centrifuged and the plasma was stored on top of the cell pellet at room temperature. After 2 h, 4 h, 6 h, 12 h and 24 h, the prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), fibrinogen concentration, antithrombin activity, D-dimer concentration and thrombin time were measured using Sysmex CS2100 coagulation analysers. Results and conclusion: Analytical evaluation of routine coagulation tests resulted in various significant differences and large variations between the various time intervals. Our results indicated that the PT and INR can be measured up till 24 h of storage. Centrifuged blood for measuring the fibrinogen concentration, antithrombin activity, D-dimer concentration and thrombin time can be stored up to 4 h, while 2 h of storage might already be long for obtaining reliable aPTT measurements