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Introduction A maximum delay between blood collection and coagulation testing of 4 hours is recommended by most guidelines. As information on optimal storage times is limited, we investigated the potential effect of different storage times of unspun tubes, that is, ≤2, 4, 6, and 8 hours, on routine coagulation test results. Methods Four evacuated polymer tubes containing 0.109 mol/L tri-Na citrate were drawn from 144 patients, including 39 patients on vitamin K-antagonists. Except for storage time, all tubes underwent the same preanalytical process. Prothrombin time ( PT)/international normalized ratio ( INR), activated partial thromboplastin time ( aPTT), fibrinogen, factor V ( FV), FVIII, and D-dimer were evaluated in two centers using the same technical conditions. Results Analytical comparison of aPTT, fibrinogen, FV, and FVIII results evaluated after prolonged storage times vs a <2-hours storage demonstrated significant difference, whereas PT/ INR and D-dimer remained unchanged up to 8 hours. Mean bias between test results obtained after prolonged storage times remained below the desirable values for all studied parameters except for FVIII evaluated after 6- and 8-hours storages, but only in patients with FVIII above 100 IU/ dL. Even though the corresponding bias of −5.2% and −8.5%, respectively, remained within the GEHT recommended limits of variation, its evaluation after an 8-hours storage could lead to significant underestimation of FVIII. Conclusion These results suggest that, in the studied technical conditions, PT/ INR, aPTT, fibrinogen, FV, and D-dimer can be reliably evaluated in tubes stored unspun at room temperature for up to 8 hours after blood collection. That optimal delay should be of 6 hours for FVIII. [ABSTRACT FROM AUTHOR] more...