PB0159 - Assessment of the impact of underfilled samples on Coagulation laboratory tests using Sysmex CN6000 analysers.

Background: Many preanalytical variables affect clotting results. Fill volume of sodium citrate tubes and ratio of sodium citrate:plasma are critical preanalytical issues. As calcium bound by citrate is replaced within reagents of clotting tests (e.g., PT, APTT), excess citrate in test plasma from low fill volume would bind reagent calcium, producing artifactually prolonged clotting time values. Current guidelines dictate a 9:1 blood to anticoagulant volume ratio.

Aims: ICSH guidance recommends rejection of samples with less than 80% fill. In my centre, we accept samples with 80-100% fill based on obtained data. The aim is to assess whether 80% fill is still appropriate. If < 80% fill volume doesn't lead to clinically important changes, rejection rate will improve. This has cost benefits and, more importantly, favourable implications for the patient due to reduced turnaround times.

Methods: Blood samples were collected from healthy volunteers (n=20) in 2.7ml Becton Dickinson vacutainer tubes (3.2%), with filling to 60, 70, 80, 90, and 100% of target. After centrifugation at 2000g for 10mins, plasma was aliquoted from each sample and stored at –800C. The samples were batch tested on the Sysmex CN6000 over several days to minimise bias.
Tests performed were Prothrombin Time, Activated Partial Thromboplastin Time, Thrombin Time, Clauss Fibrinogen, and D-Dimer.

Results: See table attached.

Conclusion(s): Data confirms 80% fill is an acceptable level for PT and APTT in normal subjects. Reduced fill volumes had less impact on Fbg and underfilling down to 60% did not introduce clinically significant changes. There is little variance in D-dimer results with maximum mean difference of 23ng/ml. The above data confirms we can accept underfilled tubes down to 80% fill these tests performed on Sysmex CN6000.