Assessment of Stability of Prothrombin Time, International Normalized Ratio, and Activated Partial Thromboplastin Time Under Different Storage Conditions in Human Plasma

Background In this study, we aimed to determine the effects of storage time and temperature on commonly performed coagulation tests such as prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (APTT) in human plasma. Methodology Whole blood samples from 100 patients were collected in a 3.2% sodium citrate vacutainer. The blood was centrifuged within two hours of collection at 2,000 g for 10 minutes, and the platelet-poor plasma (PPP) obtained was analyzed for PT, INR, and APTT tests at zero hours (baseline) and repeated at 12 hours, 24 hours, and 36 hours on a fully automated coagulation analyzer at various storage conditions (room temperature, refrigerator, and freezer). The results were categorized into two groups: group 1 comprised results with normal coagulation profile and group 2 comprised results with abnormal coagulation profile. The percentage change of the results from baseline (zero hours) for PT, INR, and APTT tests was also studied. A percentage change of more than ±10% from baseline was considered as a clinically significant change. Results In this study, a total of 95 PPP samples were evaluated. The median age of all patients was 44 years (range: 19-65 years). The male-to-female ratio was 0.9:1. The baseline PT, INR, and APTT values were 12.1 seconds, 1.06, and 26.5 seconds, respectively, in group 1, whereas the baseline PT, INR, and APTT values were 19.1 seconds, 1.80, and 36.0 seconds, respectively, in group 2. In the freezer, the samples were stable for PT, INR, and APTT tests at 12 hours, 24 hours, and 36 hours showing a change of <10% from baseline at all three time-points. In the refrigerator, the samples were stable for PT and INR tests for up to 24 hours showing a change of <10% from baseline. In comparison, the samples for the APTT test were not stable at 12 hours, 24 hours, and 36 hours showing a change of 12.1%, 15.5%, and 17.9%, respectively, from the baseline (zero hours). Finally, at room temperature, the samples deteriorated at 12 hours for all coagulation parameters (PT, INR, and APTT). Conclusions The patient plasma samples for PT, INR, and APTT tests could be safely stored for up to 36 hours in the freezer. In the refrigerator, samples for PT and INR tests could be safely stored for up to 24 hours while the samples for APTT deteriorated at 12 hours. All patient samples for PT, INR, and APTT tests deteriorated at 12 hours at room temperature.