Clinical II Lab Practical 2026 - Free Lab Supplies and Procedures Practice Questions and Study Guide

The main idea here is to prevent cross-contamination of additives and preserve the integrity of each test. The correct sequence starts with blood culture tubes when used, so any skin flora and initial contamination don’t affect cultures. Next come the light-blue tubes, which contain sodium citrate and are used for coagulation studies; they must be collected in the correct blood-to-anticoagulant ratio (and usually filled to the proper volume) to yield accurate PT, aPTT, and similar results. After that, you collect serum tubes—red (no additive) and gold with a serum separator gel—for serology and chemistry because they produce serum rather than plasma. Following those are the green-top tubes, which contain lithium heparin and are used for plasma chemistry tests that don’t require clotting. Then come the lavender-top tubes, with EDTA, which preserve cells for hematology analyses like CBCs. Finally, the gray-top tubes, which contain potassium oxalate and sodium fluoride and are used for glucose testing (the fluoride inhibits glycolysis to preserve glucose) and are drawn last to minimize any potential interference with tests drawn earlier.

In short, the order is blood cultures first (if used), light-blue, red/gold, green, lavender, and gray, with the corresponding additives: sodium citrate in the light-blue tube; no additive or a serum separator in red/gold; lithium heparin in green; EDTA in lavender; and potassium oxalate with sodium fluoride in gray. This arrangement helps prevent additive carryover and preserves each test’s accuracy.