Failure to monitor warfarin prescription

On February 25, a 51-year-old woman came to see an iternal medicine (IM) physician for a new patient visit and to refill her existing prescriptions. At this visit, the patient saw an advanced practice registered nurse (APRN). The patient reported having mitral valve replacement surgery with a mechanical valve two years before and that she was taking warfarin daily.

‍

Read the full case study below.

by Wayne Wenske, Senior Marketing Strategist

‍
Presentation and physician action

On February 25, a 51-year-old woman came to see an iternal medicine (IM) physician for a new patient visit and to refill her existing prescriptions. At this visit, the patient saw an advanced practice registered nurse (APRN).
 
The patient reported having mitral valve replacement surgery with a mechanical valve two years before and that she was taking warfarin daily. For nine months after surgery, the patient followed up with a cardiologist for prescription management and INR checks. At her last visit with the cardiologist, her INR was 2.1. Shr was taking warfarin 7.5 mg on weekend days and 5 mg on weekdays.
 
The patient’s history included hypertension, prediabetes, hyperlipidemia, extreme obesity, and excessive smoking (approximately 2.5 packs of cigarettes daily). The patient also had a sedentary lifestyle and was inconsistent with having her INR levels checked.
 
The APRN refilled the patient’s prescriptions of furosemide 40 mg (30 tablets); potassium chloride 20 mEq (90 tablets); sotalol 80 mg (30 tablets) and warfarin 5 mg (90 tablets). The patient’s INR — which was tested in the office — was 1.0.
 
There was no record that the IM physician was notified of this test result and no adjustments were made to the patient’s warfarin regimen.
 
On August 10, the patient returned to the IM physician for a physical exam required by her employer. On the employer’s form — which was to be verified by the physician — the patient did not include the mitral valve replacement nor the warfarin prescription. The IM physician signed off on the form.
 
The patient returned to the IM physician’s office twice between August 10 and April 28 of the following year. At each of these visits, her warfarin prescription was refilled with a note in the patient record: 'Blood sent to lab.' However, the specific labs, tests ordered, and test results were not documented. Documentation did not include formal visit summaries or plan of care.
 
On May 15, the patient experienced slurred speech and paralysis of the right arm and leg while at work and was taken to a local emergency department (ED) where her INR was measured at 1.4.
 
She was diagnosed with a large left middle cerebral artery acute infarction. Her ejection fraction was 20 to 25 percent. The patient was discharged on June 5 with a wearable cardioverter defibrillator.

‍
Allegations

The patient filed a lawsuit against the IM physician and the APRN for failure to monitor anticoagulation levels while prescribing warfarin, resulting in an acute ischemic cerebrovascular accident (CVA).

‍
Legal implications

Expert consultants for the defense were not supportive of the defendants’ actions. The concerning issue was that no one was monitoring the patient’s INR — including the patient. They all believed that the patient’s CVA may have been avoided had more attention been given to her history, physical condition, and noncompliance with regular INR checks.
 
At minimum, these consultants stated that the patient should have been closely monitored with monthly INR checks if levels are in range or every two weeks if levels are not in range, with adjusted dosing as needed.
 
More than one consultant pointed out that mechanical heart valves, such as the one the patient has, are prone to clots if blood is not properly anticoagulated.
 
These consultants also believed that the patient held some responsibility for the outcome. They stated that her lack of attention to modifying her behaviors (diet, smoking, physical activity, failure to obtain regular INR checks) put her at risk of either a thrombotic/embolic event, bleeding episode, or sudden cardiac death irrespective of her INR level at the time of the CVA.
 
The plaintiff’s consultants stated that the defendants failed to monitor the patient’s INR values and manage her warfarin medication respective to those levels. Specifically, failures occurred in not ordering and following up with routine lab work before authorizing refills. There were also failures in communication and documentation resulting in the IM physician not being aware of testing or results.
 
They also criticized the IM physician for not properly delegating medical acts performed by the APRN and for signing off on the patient’s employer’s physical exam paperwork without noting and addressing the patient’s omission of mitral valve replacement or warfarin prescription.

‍
Disposition

The case was settled on behalf of the IM physician and APRN.

‍
Risk management considerations

Effective warfarin monitoring is crucial for preventing both thrombotic events and bleeding complications. The narrow therapeutic window of warfarin means that careful monitoring of INR levels is essential for patient safety.
 
A patient’s compliance with testing and returning for follow-up requires patients to be an active participant in their own care. However, the responsibility of safe anticoagulation therapy also lies with the prescribing physician.
 
Losing track of a patient who requires careful monitoring places the patient and the physician at risk. It is recommended to schedule regular INR testing and follow-up appointments with the patient upon prescribing the anticoagulant. If an appointment is not kept, contact the patient immediately and document this action in the medical record.
 
It is important to maintain written policies and procedures to track and follow up with lab work, testing, and referrals, with special consideration made to critical INR test results. These policies should include documenting a patient’s baseline INR, current dosage, and the patient’s INR tracked over time. Additional considerations include the following. 

• Develop a tracking system for all labs, diagnostic studies, and referrals. This can be done via your EHR or in an electronic or paper log.
• Identify for each patient how often to monitor INR, including critical values (both high and low) for the specific patient.
• Identify those patients at risk for noncompliance, either due to language barrier, repeated no-shows, comprehension levels, etc.
• Instruct staff members or outside labs to orally notify you of a patient’s critical INR test results.
• Initial and date or electronically sign all laboratory and diagnostic reports upon your review of the report. Develop protocols to ensure that documents are not filed before your review.
• Document follow-up actions for critical or abnormal test results.
• Identify someone in your office to be available to receive and act upon critical results after hours.

If a patient regularly fails to return for INR testing, contact the patient by phone, written letter, and HIPAA-compliant messaging. Retain copies of the communication and document when it was sent and by what means. Document each attempt to contact a patient regarding a missed appointment or critical test result.
 
While a physician who orders diagnostic testing or anticoagulation medication is ultimately responsible for obtaining and acting on test results, all providers caring for the patient can help to ensure results are reviewed and communicated in a timely manner. This includes timely review of critical lab results and planning appropriate follow up, such as any changes to anticoagulation dosages. ^1
‍

More about failure to follow-up

More about medication errors

Source
 

1. Wenske W. Prescribing anticoagulants – A risk management overview. Reporter Q1 2022. Texas Medical Liability Trust. Available at https://cdn.prod.website-files.com/6790ae6ff3e4aa35f74b86d5/67bdc0b44812fa6c119fa724_reporter-q1-2022.pdf.  Accessed March 7, 2025.

‍