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Coding when managing warfarin therapy; billing when you're not the physician of record


Learn the appropriate codes that you can use for reporting the monitoring of warfarin dosage for certain patients.

Key Points

A: Codes 99363 and 99364 are used to report the outpatient management of warfarin therapy. These codes represent ordering, review, interpretation of testing, and communication with the patient to make appropriate adjustments to dosage.

Code 99363 is for the initial 90 days of therapy and must include a minimum of 8 INR measurements. Code 99364 is for each subsequent 90 days of therapy and must include at least 3 INR measurements.


Q: Should an internist use inpatient code 99221–99223 or inpatient code 99231–99233 to bill for reimbursement when a patient whose care is covered by Medicare has been admitted by another physician and the internist subsequently is called in for medical management of a separate condition?

An example would be if an orthopedist admitted a patient for a knee replacement, billed his initial service day with 99223AI, and then contacted the internist to follow the patient for benign hypertension the next day. The care of the patient has not been transferred to the internist, and the orthopedist still will be following the patient daily. So what would be the proper billing code if the orthopedic surgeon transferred the care to the internist the next day? Would the internist then bill 99223AI?

A: The admitting physician is the only provider who should submit the AI modifier. The AI modifier indicates the principal physician of record, in this case the orthopedist who admitted the patient to a surgical service and requested evaluation of the patient's co-morbidities by other physicians.

If the internist is called in to evaluate the patient's benign hypertension, then the internist may bill the initial hospital care code representing the service to the patient that was performed but may not bill the AI modifier for that patient during the same hospital stay. Subsequent hospital care should be reported with subsequent hospital care codes.

If the orthopedist transfers the care of the patient to the internist immediately following surgery (for example, if the specialist is providing surgical care in a small community, where that care otherwise would not be available), then the orthopedist should bill for the surgical care only, using the modifier 54 to indicate that only the surgical service was performed.

The internist would bill postoperative management only as a global service, using the modifier 55 (postoperative management only) to indicate that service. If more than the postoperative care was performed (for instance, management of the patient's hypertension or other health problem), then subsequent hospital services codes should be used to report that care, and the level of care chosen would be based solely on the services required to manage those other medical conditions. The modifier 24 (unrelated E/M service by the same physician during a postoperative period) should be attached to the level of subsequent hospital care. These would be extenuating circumstances, so the claim for this scenario probably would have to be reviewed.

The author is a consultant/trainer for gloStream, an electronic medical record/practice management company headquartered in Troy, Michigan; president of Healthcare Consulting Associates of NW Ohio Inc., Waterville; and a Medical Economics editorial consultant. She is a practice management consultant, certified coding specialist, certified compliance officer, and certified medical assistant. Send your primary care-related coding questions to

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Jennifer N. Lee, MD, FAAFP
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