Oral anticoagulation with warfarin is used for the treatment and prevention of a variety of thrombotic disorders, including deep venous thrombosis (DVT), pulmonary embolism (PE), stroke prevention in atrial fibrillation (AF) and atrial flutter, and other hypercoagulable conditions. Although a mainstay in the treatment for these conditions, warfarin requires close monitoring due to its narrow therapeutic range, extensive drug and dietary interactions, and dosage variability among patients.1 Patients outside the therapeutic range are at risk of having a thrombotic or bleeding event that could lead to hospitalization or fatality.1 To reduce the risk of these events, patients on warfarin are managed by dose adjustment based on the international normalized ratio (INR). Research has shown that patients on warfarin in pharmacist-managed specialty anticoagulation clinics have more consistent monitoring and lower rates of adverse events (AEs) compared with traditional physician or nurse clinics.2-6 Management through these clinics can be achieved through office visits or telephone visits.
There are advantages and disadvantages to each model of anticoagulation management for patients.Telephone clinics provide time and cost savings, increased access to care, and convenience. However, disadvantages include missed phone calls or inability to contact the patient, difficulty for the patient to hear the provider’s instructions over the phone, and patient unavailability when a critical INR is of concern. Office visits are beneficial in that providers can provide both written and verbal instruction to patients, perform visual or physical patient assessments, and provide timely care if needed. Disadvantages of office visits may include long wait times and inconvenience for patients who live far away.
Telephone anticoagulation clinics have been evaluated for their efficacy and cost-effectiveness in several studies.5,7,8 However, few studies are available that compare patient outcomes between office visits and telephone visits. Two prior studies comparing groups of anticoagulation patients managed by telephone or by office visit concluded that there is no difference in outcomes between the 2 management models.9,10 However, a retrospective study by Stoudenmire and colleagues examined extreme INR values (≤ 1.5 or ≥ 4.5) in each management model and found that telephone clinic patients have a significant increase in extreme INR values but no difference in AEs between the 2 management models.11
The VA North Texas Health Care System (VANTHCS) includes a major medical center, 3 outlying medical facilities, and 5 community-based outpatient clinics (CBOCs). A centralized pharmacist-managed anticoagulation clinic is used to manage more than 2,500 VANTHCS anticoagulation patients. To meet the National Patient Safety Goal measures and provide consistent management across the system, all anticoagulation patients from CBOCs and medical facilities are enrolled in the clinic.12 To facilitate access to care, many patients transitioned from office visits to telephone visits. It was essential to evaluate the transition of patients from office to telephone visits to ensure continued stability and continuity of care across both models. The objective of this study was to determine whether a difference in anticoagulation outcomes exists when patients are transitioned from office to telephone visits.
Methods
The VANTHCS anticoagulation clinic policy for office visits requires that patients arrive at the Dallas VAMC 2 hours before their appointment for INR lab draw. During the office visit, the anticoagulation pharmacist evaluates the INR and pertinent changes since the previous visit. The patient is provided verbal instructions and a written dosage adjustment card. Telephone clinic protocol is similar to office visits with a few exceptions. Any patient, regardless of INR stability, may be enrolled in the telephone clinic as long as the patient provides consent and has a working telephone with voice mail. Patients enrolled in the telephone clinic access blood draws at the nearest VA facility and are given a questionnaire that includes pertinent questions asked during an office visit. Anticoagulation pharmacists evaluate the questionnaire and INR then contact the patient within 1 business day to provide the patient with instructions. If a patient fails to answer the telephone, the anticoagulation pharmacist leaves a voicemail message.
Study Design
This retrospective study was conducted by chart review using Computerized Patient Record System (CPRS) at VANTHCS on patients who met inclusion criteria between January 1, 2011 and May 31, 2014, and it was approved by the institutional review board and research and development committee. The study included patients aged ≥ 18 years on warfarin therapy managed by the VANTHCS anticoagulation clinic who were previously managed in office visits for ≥ 180 days before the telephone transition, then in telephone visits for another ≥ 180 days. Only INR values obtained through the VANTHCS anticoagulation clinic were assessed.
Patients were excluded from the study if they were not managed by the VANTHCS anticoagulation clinic or received direct oral anticoagulants (DOACs). The INR values were excluded if they were nonclinic related INR values (ie, results reported that do not reflect management by the anticoagulation clinic), the first INR after hospitalization, or INRs obtained during the first month of initial warfarin treatment for a patient.
For all patients included in the study, demographic information, goal INR range (2 to 3 or 2.5 to 3.5), indication for warfarin therapy, and duration of warfarin therapy (defined as the first prescription filled for warfarin at the VA) were obtained. Individual INR values were obtained for each patient during the period of investigation and type of visit (office or telephone) for each INR drawn was specified. Any major bleeding or thrombotic events (bleed requiring an emergency department [ED] visit, hospitalization, vitamin K administration, blood transfusion, and/or warfarin therapy hold/discontinuation) were documented. Procedures and number of hospitalizations also during the investigation were recorded.
The primary outcomes measures evaluated INRs for time in therapeutic range (TTR) using the Rosendaal method and percentage of INRs within range.13 The therapeutic range was either 2 to 3 or 2.5 to 3.5 (the “strict range” for INR management). Because many patients fluctuate around the strict range and it is common to avoid therapy adjustment based on slightly elevated or lower values, a “nonstrict” range (1.8 to 3.2 or 2.3 to 3.7) also was evaluated.14 The secondary outcomes examined differences between the 2 management models in rates of major AEs, including thrombosis and major bleeding events as defined earlier.Frequencies, percentages, and other descriptive statistics were used to describe nominal data. A paired t test was used to compare TTR of patients transitioned from office to telephone visits. A P value of < .05 was used for statistical significance.