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.
Indevuyst, C., Schuermans, W., Bailleul, E. and Meeus, P. (2014) The order of draw: much ado about nothing? International Journal of Laboratory Hematology. April 8th. (epub ahead of print).