Effect of storage time on prothrombin time and activated partial thromboplastin time: study at a tertiary care center in Kashmir valley

Background: Prothrombin time (PT) and activated partial thromboplastin time (APTT) are tests of haemostasis commonly employed in the evaluation of coagulopathies. Storage temperature and time interval between sample collection and testing can have a significant effect on results of coagulation tests. The aims of the study were investigate whether storage temperature and time influence the results of routine coagulation tests and whether any changes caused by delayed analysis results in a clinically relevant difference, as well as to establish our own acceptable storage temperature and time guidelines. Methods: This study was conducted at Department of Clinical Haematology, in a tertiary care center in Kashmir valley. This study included 50 cases. Individuals with chronic liver diseases or cardiovascular disorders, subjects on anticoagulant therapy were excluded. 25 samples were observed at room temperature (RT) and 25 samples at 2-8°C. PT and APTT was measured at 0, 2, 4, 8, 16 and 24 hours both at RT and 2-8°C. Findings at 0 hr were compared to findings at 2,4, 8,16 and 24 hours in both the groups. Results: In case of PT, reliable results were obtained up to 24 hrs either kept at RT or at 2 to 8°C and for APTT reliable results were obtained up to 4 hours kept at RT or at 2 to 8°C as there was no significant change during this period. Conclusions: Coagulation test should be performed as soon as possible with PT being performed before 24 hours and APTT before 4 hours of collection of sample irrespective of whether the sample has been preserved at RT or in refrigerator.