Phlebotomy training and competency assessment should include a review of the correct order of draw during venipuncture to help to ensure accurate test results. The Clinical Laboratory Standards Institute (CLSI) publishes a recommended order of draw for evacuated blood collection tubes (see image). This order of draw is for use with straight needle or tube holder draws as well as syringe draws.
An incorrect order of draw may lead to an incorrect test result. Drawing an EDTA tube (containing potassium) prior to a red-top or gel-separation tube for chemistry testing may easily contaminate the needle and introduce anticoagulant to the chemistry tube leading to a possible elevated potassium and decreased calcium results. This can lead to possible misdiagnosis or incorrect treatment of the patient.
A winged blood collection device (butterfly) can be used for collecting a specimen as well. If it is used for coagulation studies, a waste tube must be drawn first. The waste tube is drawn to remove the air in the tubing of the winged collection device. The waste tube must also be a light-blue top tube (sodium citrate) or a tube that contains no additives or anticoagulants. A red-top tube that contains a clot-activator cannot be used as activator can transfer to the blue top tube and affect the test results.
Once blood flows through the tubing, the waste tube can be removed and discarded. The waste tube does not need to be completely filled. If the air is not displaced from the tubing into a waste tube, it will be drawn into the tube used for testing and cause a short-fill of the tube. An inadequately filled tube will alter the required blood-to-anticoagulant ratio needed for coagulation studies, adversely affecting results. Additional tubes can be collected, using the proper order of draw, after the coagulation tube has been drawn. A separate venipuncture is not required.
Reference: Clinical and Laboratory Standards Institute (CLSI). Collection of Diagnostic Venous Blood Specimens; Approved Standard. 7th ed. CLSI document GP41. Wayne, PA: CLSI; 2017.
