Washington Subscriber
Answer: Medicare's National Coverage Determination for Prothrombin time lists V58.61 (Long-term [current] use of anticoagulant) as a payable diagnosis for 85610. You may also code the underlying condition as a secondary diagnosis if it's provided by the ordering physician, although it is not absolutely necessary. For example, if the physician order states that the patient has atrial fibrillation, you can report 427.31 (Atrial fibrillation) as the secondary diagnosis.