Effect of Pre-analytical Conditions on Prothrombin Time and Partial Activated Thromboplastin Time

Clinical analysis often involves clotting assays. Although the guidelines suggest the storing and freezing of samples before these assays, there are contradictory results in the literature. The objective of this study was to analyse the effect of the temperature and the storage of plasma sample on Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT) in clinical samples for 65 patients without coagulation disorders.

After centrifugation, plasma of each patient was tested at arrival as part of their routine care and separately aliquoted. Three aliquots were stored at room temperature, 4°C and - 20°C for 24h after collection, two aliquots were stored at 4°C and -20°C for 1 week and one aliquot was stored at -70°C for 1 month.

PT from healthy patients was affected at room temperature for 24h and at 4°C for 1 week. For aPTT, the results were statistically different for all the conditions after 24h and at 4°C for 1 week.

Results indicate that PT and aPTT can be stored at -70ºC for at least 1 month without any significant changes in the assay result.