A PCT receives orders for blood cultures, a light-blue coagulation tube, a serum separator tube, and a lavender EDTA tube from a single venipuncture on an adult with no IV fluids infusing. The kit contains sterile culture bottles, citrate, clot activator, and EDTA additives. Which collection order should the PCT follow to apply order of draw and tube additives correctly?

The correct sequence protects sterility and additive integrity because sterile blood cultures must precede all tubes to avoid skin flora and chemical contamination, followed by light-blue citrate for coagulation testing which is highly sensitive to tissue thromboplastin and calcium chelation, then the serum separator tube with clot activator, with lavender EDTA last because its potassium salt irreversibly binds calcium. The sequence placing serum separator before citrate preserves sterility but fails additive order because clot activator carryover can activate clotting factors and distort prothrombin and partial thromboplastin results. The sequence placing lavender EDTA between citrate and serum also preserves sterility but fails because EDTA carryover falsely elevates potassium, depresses calcium and magnesium, and interferes with enzymes and immunoassays, violating the serum-before-EDTA hierarchy. The sequence placing lavender EDTA immediately after cultures is most harmful to coagulation testing because even trace EDTA chelates calcium and invalidates the precise 9:1 blood-to-citrate ratio required for calcium-dependent clot formation. An exam caveat is that no IV fluids infusing confirms routine venipuncture without dilution, so no discard tube or altered progression is needed for this adult single draw. As a practical check, the PCT should verify expirations, maintain sterile bottle transfer, ensure complete vacuum fill especially for citrate, invert tubes gently the specified times without shaking, and label at the bedside after collection.