Which specimen can be centrifuged immediately upon arrival in specimen processing?

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Immediate centrifugation is appropriate when the tube contains an anticoagulant that prevents clotting, so you can separate plasma right away. A green-top tube uses heparin as the anticoagulant, which keeps the blood from clotting and allows quick spin to yield plasma for chemistry tests, such as calcium measurement. Measuring calcium in a tube that contains EDTA (lavender-top) would be unreliable because EDTA binds calcium and alters the result, so it isn’t spun down for this test. The other specimens have handling requirements that preclude immediate centrifugation: a blood culture tube is processed for culture rather than spun to obtain plasma, a clot-activator SST tube must clot before centrifugation to yield serum, and a CBC in a lavender (EDTA) tube is used with whole blood for hematology rather than plasma.