The order of draw

Speaker: Michael Cornes (UK)
Moderator: João Tiago Guimarães (PT)

Recorded on 15th May 2018

Abstract

National and international (WHO, CLSI) guidelines recommended that order of draw of blood during phlebotomy should be blood culture/sterile tubes, then plain tubes/gel tubes, then tubes containing additives. This prevents contamination of sample tubes with additives from previous tubes for example sodium citrate or more commonly potassium EDTA (K3EDTA).

These recommendations are based on a case report by and a follow up study by Calam and Cooper in 1982 which reported that incorrect order of draw caused hyperkalaemia and hypocalcaemia. By measuring EDTA, it has been demonstrated that reverse order of draw of blood samples using closed loop venesection systems does not cause EDTA contamination. It is difficult to reconcile the directly conflicting results of these studies but it may be that reversed order of draw using poor technique and/or difficult venepuncture may result in sample tube cross-contamination.

It has been shown that contamination is still relatively common and may be difficult to identify. As this is not due to reversed order of draw of blood samples in a closed loop system other mechanisms must be in operation. Here I will present the evidence for and against the need to follow an order of draw.