PB1089 - Evaluation of the effect of freezing and thawing of citrated plasma on coagulation assays

Background: Routine coagulation results can be affected by various pre analytical factors that includes the stability of the citrated plasma at room temperature. The current BSH guideline recommends that coagulation assays should be performed within 4 hours from sample collection, however this is not always possible.

Aims: To evaluate the impact of freezing and thawing of citrated plasma on routine coagulation assays.

Methods: Blood samples were collected into 3.2% sodium citrate tubes, spun and analysed for prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, thrombin time (TT), reptilase time (RT) and D-dimer. Plasma aliquots were then separated into screw-top microvials and stored in a -80⁰C freezer for at least 2 weeks. The plasma aliquots were then thawed at 37⁰C for 4 minutes and re-tested using the same reagents lots. All analyses were performed on the Sysmex CN6000 analysers using Siemens reagents (Siemens, Healthcare Diagnostics, Marburg, Germany). The difference between fresh and frozen sample results were determined using Wilcoxon test (p < 0.05 indicating statistically significant differences). Areas of bias were evaluated using Bland and Altman plots.

Results: Median (range) and p values for all assays are presented in table 1. The Wilcoxon analysis showed a statistically significant differences between fresh and frozen results for PT, TT, RT and D-dimer.

Conclusion(s): We demonstrated that freezing and thawing conditions affect PT, TT, RT and D-dimers with a statistical significance, however these differences are not considered to be clinically significant.