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The order of draw: much ado about nothing?
C Indevuyst1, W Schuermans, E Bailleul
1Laboratory of Hematology, Onze-Lieve-Vrouw Ziekenhuis, Aalst, Belgium.
Introduction:
The 'order of draw' has been advocated since 1982 to reduce the risk of cross-contaminating blood tubes with additives from a previously filled tube.
Methods:
We studied 193 patients receiving oral anticoagulation. Multiple tubes were collected in a specific order using the Sarstedt Safety Monovette System. We evaluated the effect of the 'order of draw' on the prothrombin time/international normalized ratio (PT/INR) and the activated partial thromboplastin time (APTT) when the citrate tube is drawn as the first tube, second tube or after a heparin, EDTA or serum tube with clot activator.
Results:
There was no statistically significant influence on the PT/INR. The same applies for the APTT measured on a citrate tube drawn after a heparin tube. There was a small, but statistically significant bias on the APTT when the citrate tube was drawn as the first tube, after an EDTA tube or after a serum tube with clot activator. We consider this bias (max. 0.2 s) as not clinically significant.
Conclusion:
The order of draw has no significant influence on the PT/INR and APTT when measured on a Sarstedt citrate tube filled without the use of a discard tube or after a heparin, EDTA or serum tube with clot activator.
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