Patient Self-Testing of Prothrombin Time After Hip Arthroplasty

C. Anderson Engh, Jr., MD, William J. Culpepper II, MA, Patricia A. Charette, RN and Rachel Brown, from the Anderson Orthopaedic Research Institute, Alexandria, Va.

J South Orthop Assoc. 2001;10(3) 

In This Article

Materials and Methods

The patients included in this study, which was approved by the Institutional Review Board, were Medicare beneficiaries who were scheduled for THA, who lived within an hour of our institution, and who were mentally and physically capable of participation. (Patients with dementia, Parkinson's disease, or disability of the upper extremities were excluded.) We selected Medicare patients because the fixed reimbursement rate for home health visits made it easier to contract with one home health agency and to estimate the costs associated with the home health nurse. The geographic restriction made it possible to use a single home health agency. Of 78 patients who met the inclusion criteria for participation, 46 (59%) consented to participate and enrolled in the study.

The CoaguChek (Figure) is a battery-powered, portable device that uses laser photometry to measure prothrombin time. A drop of whole blood (about 25 mL), obtained through a fingerstick, is applied to a thin plastic cartridge with an enclosed capillary channel. Capillary action draws the blood into a chamber, where it mixes with rabbit brain thromboplastin. As the blood clots, the laser photometer detects the cessation of movement by sensing the changes in light scattering caused by the red blood cells. The elapsed time is converted to a plasma-equivalent prothrombin time, which is displayed either in seconds or INR units.

CoaguChek device

Validation and reliability studies of the CoaguChek have shown that the intertest coefficient of variation ranges from 2.4% to 4.2%. Correlations between .96 and .99 have been found when the CoaguChek results were compared with those of reference plasma prothrombin time tests done in the laboratory.[10,14,15] When this study began, the Food and Drug Administration had approved the CoaguChek for professional use only; during the study, approval for patient self-testing was granted.

At their preoperative evaluation (before THA), all patients were briefed about the study by their surgeon. The research nurse discussed specific procedures and requirements of participation with each patient. The nurse also obtained written informed consent in keeping with Institutional Review Board requirements. Once informed consent was given, patients were scheduled for two training sessions. The research nurse, trained and certified by the manufacturer as a clinical instructor, performed all patient education. The first session, scheduled to coincide with a preoperative visit to the hospital, began with a 12-minute video that demonstrated the use of the CoaguChek (the self-testing device). The research nurse then reviewed the procedures and performed a test on herself. After this, the patient performed a test. Multiple attempts were allowed to give the patient ample opportunity to obtain a valid result and become comfortable with the device and procedures. The second training session was given on the fourth postoperative day before discharge from the hospital. At this session, the research nurse observed the participant's skill in using the device.

Patients were instructed to do two prothrombin time tests using the self-testing device each week for the next 6 weeks. They were to do one self-test on their own and the other in the presence of the visiting home-health nurse. The home-health nurse also performed a test with the self-testing device immediately after the patient and then did a venous blood draw. After completing the visit, the home-health nurse transported the blood sample to the designated laboratory for testing. Laboratory personnel phoned the result to the clinic nurse who recorded the value on the patient's data sheets. The procedures for handling and transporting blood specimens were in keeping with Clinical Laboratory Improvement Act guidelines.[16]

After each self-test, the patient called the nurse at the surgeon's office to report the result in INR units. The clinic nurse adjusted the patient's Coumadin dosage to maintain the value between 1.5 and 2.5. The patient also recorded the date, time, and result of each self-test and the number of attempts required to obtain a valid result in a data log. The clinic nurse maintained a similar record. All patient self-test results were stored in the memory of the self-testing device and were downloaded after each patient completed the study protocol.

All patients received 5 mg of Coumadin the night before surgery. While in the hospital, they were managed with a sliding-scale dosage of Coumadin based on INR values obtained from venipuncture-laboratory testing. Coumadin was discontinued at the 6-week follow-up visit if a screening venous Doppler study was negative for deep vein thrombosis. The 6-week follow-up visit with the surgeon marked the end of the study. Patients who were unexpectedly discharged out of the service area or whose Coumadin therapy was discontinued before 6 weeks were excluded from the study.

We retrospectively obtained a matched-control group of patients who had been managed concurrently according to the same anticoagulation monitoring protocol. Prospective control patients were Medicare recipients who were mentally and physically capable of participating in the self-testing protocol. Geographic area was not a selection criteria for these patients. Control-group patients were matched to study-group patients on age, sex, weight, and diagnosis, but without our knowledge of anticoagulation status or possible complications. No differences in age, weight, sex, or overall health status existed between the two groups of patients. The same clinic nurse managed the control-group patients with the same goal of maintaining the INR value between 1.5 and 2.5 based on laboratory tests. Data were tabulated by the same method as used for the treatment group.

We maintained data in a computer database and performed statistical summaries and analyses using SPSS v7.5 (SPSS, Chicago, Ill). Analyses included (1) patient participation and compliance with the protocol; (2) reliability of patient self-testing; (3) quality of care; and (4) the relative cost savings of patient self-testing with the CoaguChek protocol compared with the cost of the standard monitoring protocol. Reliability of patient self-testing with the device was assessed by Pearson correlations and t tests for related measures. To evaluate quality of care, we compared the percentage of test results that were within the target therapeutic range (INR of 1.5 to 2.5). A cost analysis compared the relative costs of using the self-testing device and the cost of our standard testing protocol. Medicare reimbursement rates for home health visits (derived from the Medicare Carriers' Manual, Sections 4106.3 and 4106.4), laboratory prothrombin testing, CoaguChek cartridges, and CoaguChek rental were calculated. The reimbursement rates related to the CoaguChek device were provided by the manufacturer and were based on the Medicare Carriers' Manual.

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