In the order of draw for skin puncture, which item is drawn third?

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The order of draw in a capillary (skin puncture) collection is arranged to minimize contamination from tissue fluid and additives and to preserve the integrity of each test. Start with a specimen intended for measurements that are most easily distorted by contact with tissue fluid and by delays, such as a blood gas sample, which needs to be collected into a suitable anticoagulant without contamination. Next, obtain a blood smear on a slide to analyze cell morphology while the sample is fresh. After that, collect the EDTA-containing microtainer because the cells need EDTA to stay preserved for a complete blood count and related tests. Finally, draw the serum microtainer last because serum tests require proper clotting without the influence of anticoagulants. Since EDTA would interfere with serum testing if added earlier, placing the EDTA tube third keeps the serum sample uncontaminated and clotting properly.