Is platelet poor plasma used and how is APTT affected by the plasma platelet count in patient samples?

Background: Diagnostic coagulation testing is vulnerable to factors of the pre-analytical phase such as sample centrifugation. Despite this, centrifugation conditions differ widely among European laboratories. Here we use samples from patients referred for Activated partial thromboplastin time (APTT) testing to investigate if different centrifugation conditions result in platelet-poor plasma (PPP) (plasma platelet count < 10 x 109/L) and how the variation in centrifugation conditions affect APTT measurements.
Methods: Centrifugation of 2000g (10 minutes) were compared with 3000g (10 minutes) using samples from patients referred for APTT testing (n=70). Plasma platelet count and APTT were measured to investigate the influence of the centrifugation conditions. Differences were evaluated using Bland Altman Plots and Student’s t-test.
Results: Centrifugation at 3000g for 10 minutes produced PPP for more of the samples (64%) than centrifugation at 2000g (6%) (p<0.001). No statistically significant difference (p=0.265) was found for samples with APTT <37 seconds while samples with prolonged APTT showed a statistically significant difference (p=0.025). The Bland Altman plot did not reveal a clinically significant difference (mean difference 0.30 seconds/0.68%) when compared to a maximum acceptable bias of 10%.
Conclusion: None of the centrifugation conditions used in this study adequately secured PPP for all samples. Despite a statistically significant difference between samples with prolonged APTT, no clinically significant difference was observed when comparing all APTT measurements.