The nurse is evaluating the effectiveness of warfarin in a patient with atrial fibrillation. The patient's prothrombin time (PT) is 20 seconds. The nurse should anticipate


• A normal PT is 11–12.5 seconds. For patients on warfarin, the therapeutic level is 1.5 to 2 times the normal level.

• A PT of 20 seconds falls within the therapeutic range, so the dose should not be held or altered.

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