The order of draw, explained

The order of draw is the fixed sequence in which you fill collection tubes during one venipuncture. It is one of the most reliably tested topics on the NHA CPT exam, and the NHA test plan lists it as a task for both venous and capillary collection.

The sequence

The standard order, following the CLSI recommendation as republished by tube makers and hospital labs, is:

1. Blood culture bottles (yellow SPS)
2. Light blue (sodium citrate)
3. Serum tubes: red, then gold or red-speckled gel tubes
4. Green (heparin)
5. Lavender (EDTA)
6. Gray (sodium fluoride and potassium oxalate)

The tube color guide shows each tube's additive and where it sits in the sequence. Some lab charts add extras, such as ACD tubes after citrate or special additive tubes last, so on the job follow your facility's chart. The exam-style core is the six steps above.

Why the order exists

Needles and tube stoppers can carry a trace of additive from one tube into the next. The order is arranged so that any carryover lands in a tube where it does the least damage. Two concrete examples: EDTA carried into a serum or heparin tube can raise potassium and lower calcium, and clot activator carried into a citrate tube can shorten coagulation times. Blood cultures come first to protect the sterile bottles from stopper contamination.

Details that get tested

• Winged (butterfly) sets. Tubing holds air. A discard tube is needed only when the first tube to fill is a light blue citrate tube, so the citrate tube fills to the correct volume. It is not needed for every butterfly draw.
• Blood cultures with a winged set. Fill the aerobic bottle first, then the anaerobic bottle.
• Syringe draws. Tubes are filled in the same order when transferring from a syringe, using a safety transfer device and not by forcing the plunger.
• Fill and mix. Light blue tubes must be filled to the line (9 parts blood to 1 part additive) and mixed with 3 to 4 gentle inversions. Serum tubes get about 5, and heparin, EDTA and fluoride tubes get 8 to 10 per the BD chart. Too few inversions leaves additive unmixed and can cause clots or platelet clumping.
• Capillary collection has its own order, covered in unit 9 of the course.

Practice

Recognition is not enough, because exam questions hand you a random subset of tubes and ask what comes first. Run a few rounds of the order of draw quiz, then keep the sequence fresh with spaced review in the NHA CPT phlebotomy course. Related reading: phlebotomy tube colors and additives, what is on the NHA CPT exam and the testing effect.