The order of draw: much ado about nothing?
BACKGROUND
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.


CONCLUSIONS
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.
Laboratory of Hematology, Onze-Lieve-Vrouw Ziekenhuis, Aalst, Belgium.
C
C
Indevuyst
W
W
Schuermans
E
E
Bailleul
P
P
Meeus
D000925:Anticoagulants / Q000493:pharmacokinetics / Q000627:therapeutic use; D001780:Blood Coagulation Tests / Q000379:methods / Q000592:standards*; D006801:Humans; D019934:International Normalized Ratio; D010314:Partial Thromboplastin Time; D011517:Prothrombin Time; D015203:Reproducibility of Results; D013048:Specimen Handling / Q000592:standards*
D000925:Anticoagulants
Order of draw; phlebotomy; pre-analytical variability; sample collection; sample quality