Effect of Storage Time and Temperature on PT and APTT in Venous Samples

Abstract

Objectives: To assess the impact of temperature and storage time on venous blood samples for PT and APTT analysis, to compare the mean percentage changes in PT and aPTT concerning standard reference values.

Methodology: This prospective experimental study included 200 consecutive samples from subjects visiting the outpatient department and admitted subjects not receiving anticoagulant therapy at the Department of Pathology, Benazir Bhutto Hospital, Rawalpindi. The study was conducted over six months following approval of the synopsis. PT and aPTT were measured at two temperatures: 4°C (refrigerator) and 25°C (room temperature) at 0, 6, and 24-hour intervals in venous blood processed as platelet-poor plasma. Data analysis was performed using SPSS-23.

Results: Of the 200 subjects, 107 were male, and 97 were female, with an average age of 47 ± 15 years (range: 20-79 years). A total of 156 (78%) samples were from outpatient visitors, and 44 (22%) from inpatients. The findings showed a time and temperature-dependent increase in both coagulation parameters. At 25°C, the average PT increased by about 7.05% and aPTT by 47.97% after 24 hours. In contrast, samples stored at 4°C had much larger increases; the average PT rose by 65.06% and aPTT by 91.68% after 24 hours. These findings suggest that storage at 4°C results in more evident percentage increases in PT and aPTT compared to 25°C, especially over 24 hours, showing greater instability at lower temperatures.

Conclusion: Both PT and aPTT should be measured within the first 6 hours after sample collection, as their reliability decreases over time. Storage temperature has a significant effect, with lower temperatures causing greater alterations in results over time.