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.
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 anti-coagulant 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.