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The page below is a sample from the LabCE course Minimizing Pre-Analytical Variability During Venipuncture, Urine Sample Collection, and Sample Processing. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Order of Draw

The Clinical Laboratory Standards Institute (CLSI) has published a recommended order of draw for evacuated blood collection tubes (see image). 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 order of draw listed on the right is used for the Evacuated Tube System (ETS).
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 first to remove the air in the tubing of the winged collection device. The waste tube must also be a light-blue top tube or a tube that contains no additives or anticoagulants. A red-top tube that contains a clot-activator cannot be used as the clot 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, thus adversely affecting results.
A tube that contains an additive or anticoagulant other than sodium citrate (the anticoagulant present in light-blue top tubes) must not be used as the waste tube.
Additional tubes can be collected, using the proper order of draw as listed, after the coagulation tube has been drawn. A separate venipuncture is not required.
One example of an incorrect order of draw that may lead to an incorrect chemistry result is drawing an EDTA tube (contains potassium) prior to a red-top or gel-separation tube for chemistry testing. The anticoagulant from the lavender-top tube may easily contaminate the needle and introduce anticoagulant to the chemistry tube, which can lead to an elevated potassium result and decreased calcium result. This can lead to possible misdiagnosis or incorrect treatment of the patient.
Reference: Clinical and Laboratory Standards Institute (CLSI). Collection of Diagnostic Venous Blood Specimens; Approved Standard. 7th ed. CLSI document GP41. Wayne, PA: CLSI; 2017.