For accurate blood test results, much hinges on the order of draw the phlebotomist uses. There is a specific order that is to be used to avoid contamination and inaccurate results. A chart detailing this order should be posted in every phlebotomy room so that even if a phlebotomist forgets, she can immediately refer to the chart and correctly draw the specimens.
Several different types of tubes are used in blood drawing. Each tube is identified by the colour of the stopper and the additive placed in the tube. The additives each have specific functions and treat the blood in some way. They are to be drawn in the following order if using an evacuated tube system: sterile tubes, coagulation tubes, serum tubes, heparin or plasma separator tubes, EDTA tubes and glycolytic inhibitor or oxalate tubes.
Sterile tubes are larger than the usual blood collection tube and have pale yellow stoppers. Coagulation tubes have stoppers that are light blue. Serum tubes can either have a red stopper, with or without a clot activator in the bottom of the tube, a bright yellow plastic stopper or red and grey speckled rubber tops. Heparin and plasma separator tubes are topped in light green or green and grey. EDTA is found in tubes with lavender stoppers. Gray-topped tubes are oxalate tubes or glycolytic inhibitors.
It is vital that this order of draw be followed in each and every blood draw. If a sterile tube is drawn after another tube, you forfeit the sterility and risk contaminating that specimen. If drawn out of order, EDTA can still be on the needle in trace amounts and can keep the next tube from clotting the way it is supposed to. You do not want to introduce heparin, a blood thinner, to a coagulation tube, since that would skew your results.
There is sometimes a variation of order of draw when the phlebotomist is using a syringe system. Because blood begins the clotting process immediately upon entering the syringe, some institutions prefer that, if using a syringe, coagulation tubes are filled immediately following sterile tubes with the EDTA tubes being filled next. Then the tubes where clotting is necessary are filled last. Whichever order of draw is used at the institution where you work, all tubes should be filled quickly after a syringe draw to prevent problems.
At times, finger stick technique is used to perform phlebotomy. The order of draw is different than what is used for regular venous phlebotomy. During a finger stick, the puncturing of the skin immediately begins the clotting process, so it is necessary to work quickly and accurately to fill EDTA or lavender tubes first, then fill the other tubes containing additives, leaving the other tubes that allow clots for last.
The manufacturers of the evacuated tubes usually have full-colour detailed charts available that show the proper order of draw. Display these in a prominent location to prevent any mistakes.
- Phlebotomy Essentials; Ruth E. McCall, 2003