Final answer:
A serum specimen tube without anticoagulant should stand for 30 minutes to 1 hour to allow complete clotting before centrifugation. This step is essential for accurate serum separation from the cellular components.
Step-by-step explanation:
A medical assistant should allow a serum specimen tube without an anticoagulant additive to stand for approximately 30 minutes to 1 hour before centrifugation. This waiting period is crucial to ensure that the blood clots completely, and the serum can be fully separated from the cellular components. The presence of clotting is essential in serum preparation because, unlike plasma which contains anticoagulants such as EDTA, heparin, or lithium heparin, serum is the liquid fraction of blood obtained after blood has been allowed to clot and the clot has been removed by centrifugation.