Relationship between test frequency and outcomes of anticoagulation: a literature review and commentary with implications for the design of randomized trials of patient self-management

Stroke Prevention in Atrial Fibrillation: Where are We Now?

Atrial fibrillation is the commonest arrhythmia worldwide and is a growing problem. AF is responsible for 25% of all strokes, and these patients suffer greater mortality and disability. Warfarin has traditionally been the only successful therapy for stroke prevention, but its limitations have resulted in underutilisation. Major progress has been made in AF research, leading to improved management strategies. Better risk stratification permits identification of truly low-risk patients who do not require anticoagulation and we are able to simplify ourevaluation of a patient's bleeding risk.The advent of novel anticoagulants means warfarin is no longer the only choice for stroke prophylaxis. These drugs circumvent many of warfarin's inconveniences, but onlylong-term study and use will conclusively demonstrate how they compare to warfarin. The landscape of stroke prevention in AF has changed with effective alternatives to warfarin available for the first time in 60 years-but each new option brings new considerations.

Long-term self-management of anticoagulation therapy after mechanical heart valve replacement in outside trial conditions

In this investigation, we hypothesize that quality of oral anticoagulation (OA) and long-term outcome after mechanical heart valve (MHV) replacement with self-management (Self-M) of OA is superior to conventional anticoagulation treatment (Conv-T), even in outside trial conditions. One hundred sixty patients (78.8% aortic valve replacements) were trained in international normalized ratio Self-M and 260 patients (86.2% aortic valve replacements) preferred Conv-T. Mean follow-up was 8.6 ± 2.1 years, representing 3612 patient-years. During follow-up, 37.2% bleedings and 10.6% thromboembolic events were recorded in the Self-M group versus 39.6% bleedings (P = 0.213) and 15.4% thromboembolic events (P = 0.064) in the Conv-T group. Serious adverse events were significantly lower in the Self-M group [grade III bleeding events causing disability or death: 0 versus 4.6% (P = 0.03); grade III thromboembolic events: 0.6 versus 5.0% (P = 0.011)]. Patients with Self-M were significantly more satisfied with their OA management and their quality of life (P < 0.001). Actuarial survival after 1, 5 and 10 years was 100, 99 and 97 with Self-M and 100, 95 and 81% with Conv-T, respectively (P < 0.001). Univariate risk factors for mortality were age (P = 0.008), type of operation (P = 0.021) and conventional OA (P < 0.001). In multivariate analysis, only conventional OA reached significance (P < 0.001). We conclude that in a routine setting under outside trial conditions Self-M of OA improves long-term outcome and treatment quality.

Beyond the prescription: medication monitoring and adverse drug events in older adults

Whether a person will suffer harm from a medication or how severe that harm will be is difficult to predict precisely. As a result, many adverse drug events (ADEs) occur in patients in whom it was reasonable to believe that the drug's benefits exceeded its risks. Improving safety and reducing the burden of ADEs in older adults requires addressing this uncertainty by not only focusing on the appropriateness of the initial prescribing decision, but also by detecting and mitigating adverse events once they have started to occur. Such enhanced monitoring of signs, symptoms, and laboratory parameters can determine whether an adverse event has only mild and short-term consequences or major long-term effects on morbidity and mortality. Although current medication monitoring practices are often suboptimal, several strategies can be leveraged to improve the quality and outcomes of monitoring. These strategies include using health information technology to link pharmacy and laboratory data, prospective delineation of risk, and patient outreach and activation, all within a framework of team-based approaches to patient management. Although many of these strategies are theoretically possible now, they are poorly used and will be difficult to implement without a significant restructuring of medical practice. An enhanced focus on medication monitoring will also require a new conceptual framework to re-engineer the prescribing process. With this approach, prescribing quality does not hinge on static attributes of the initial prescribing decision but entails a dynamic process in which the benefits and harms of drugs are actively monitored, managed, and reassessed over time.

Risk-Adjusted Percent Time in Therapeutic Range as a Quality Indicator for Outpatient Oral Anticoagulation

Background—

Oral anticoagulation is safer and more effective when patients receive high-quality care. However, there have been no prior efforts to measure quality of oral anticoagulation care or to risk adjust it to ensure credible comparisons. Our objective was to profile site performance in the Veterans Health Administration (VA) using risk-adjusted percent time in therapeutic range (TTR).

Methods and Results—

We included 124 551 patients who received outpatient oral anticoagulation from 100 VA sites of care for indications other than valvular heart disease from October 1, 2006, to September 30, 2008. We calculated TTR for each patient and mean TTR for each site of care. Expected TTR was calculated for each patient and each site based on the variables in the risk adjustment model, which included demographics, comorbid conditions, medications, and hospitalizations. Mean TTR for the entire sample was 58%. Site-observed TTR varied from 38% to 69% or from poor to excellent. Site-expected TTR varied from 54% to 62%. Site risk-adjusted performance ranged from 18% below expected to 12% above expected. Risk adjustment did not alter performance rankings for many sites, but for other sites, it made an important difference. For example, the site ranked 27th of 100 before risk adjustment was one of the best (risk-adjusted rank, 7). Risk-adjusted site rankings were consistent from year to year (correlation between years, 0.89).

Conclusions—

Risk-adjusted TTR can be used to profile the quality of outpatient oral anticoagulation in a large, integrated health system. This measure can serve as the basis for quality measurement and quality improvement efforts.

The quality of warfarin prescribing and monitoring in Veterans Affairs nursing homes

OBJECTIVES

To describe the quality of warfarin prescribing and monitoring in Veterans Affairs (VA) nursing homes and to assess the factors associated with maintaining a therapeutic international normalized ratio (INR).

DESIGN

Retrospective cohort.

SETTING

Five VA nursing homes.

PARTICIPANTS

All veterans who received warfarin between January 1 and June 30, 2008, at the nursing homes.

MEASUREMENTS

Using medical records, the percentage of person-time spent in the target INR range, the proportion of patients with INRs in the therapeutic range on 50% or more of their person-days, and the frequency of INR monitoring were estimated. Multivariable logistic regression was used to identify factors associated with maintaining a therapeutic INR 50% or more of the time.

RESULTS

Over 6 months, 160 patients received 10,380 person-days of warfarin. INRs were in the therapeutic range for 55% of the person-days, and 99% of the INR tests were repeated within 4 weeks of the previous result. On an individual level, 49% of patients had INRs in the target range for 50% or more of their person-days. Achieving this outcome was more likely in patients with prevalent warfarin use than with new use (adjusted odds ratio (AOR)=2.86, 95% confidence interval (CI)=1.06-7.72). Conversely, patients with a history of a stroke (AOR=0.38, 95% CI =0.18-0.80) were less likely to have therapeutic INRs for 50% or more of their days.

CONCLUSION

Warfarin appears to be prescribed and monitored effectively in VA nursing home patients. Future studies should focus on increasing time in therapeutic range in patients with poor INR control.

Twelve-month outcomes and predictors of very stable INR control in prevalent warfarin users

BACKGROUND

For patients on warfarin therapy an international normalized ratio (INR) recall interval not exceeding 4 weeks has traditionally been recommended. For patients whose INR values are nearly always therapeutic, less frequent INR monitoring may be feasible.

OBJECTIVE

To identify patients with stable INRs (INR values exclusively within the INR range) and comparator patients (at least one INR outside the INR range), compare occurrences of thromboembolism, bleeding and death between groups, and identify independent predictors of stable INR control.

METHODS

The study was a retrospective, longitudinal cohort study using data extracted from electronic databases. Patient characteristics and risk factors were entered into multivariate logistic regression models to identify variables that independently predict stable INR status.

RESULTS

There were 533 stable and 2555 comparator patients. Bleeding and thromboembolic complications were significantly lower in stable vs. comparator patients (2.1% vs. 4.1% and 0.2% vs. 1.3%, respectively; P < 0.05). Independent predictors of stable INR control were age >70 years, male gender and the absence of heart failure. Stable patients were significantly less likely to have target INR > or =3.0 or chronic diseases.

CONCLUSION

A group of patients with exclusively therapeutic INR values over 12 months is identifiable. In general, these patients are older, have a target INR <3.0, and do not have heart failure and/or other chronic diseases. Our findings suggest that many patients whose INR values remain within the therapeutic range over time could be safely treated with INR recall intervals >4 weeks.

A policy model to evaluate the benefits, risks and costs of warfarin pharmacogenomic testing

BACKGROUND

In 2007, the US FDA added information about pharmacogenomics to the warfarin label based on the influence of the CYP2C9 and VKORC1 genes on anticoagulation-related outcomes. Payers will be facing increasing demand for coverage decisions regarding this technology, but the potential clinical and economic impacts of testing are not clear.

OBJECTIVE

To develop a policy model to evaluate the potential outcomes of warfarin pharmacogenomic testing based on the most recently available data.

METHODS

A decision-analytic Markov model was developed to assess the addition of genetic testing to anticoagulation clinic standard care for a hypothetical cohort of warfarin patients. The model was based on anticoagulation status (international normalized ratio), a common outcome measure in clinical trials that captures both the benefits and risks of warfarin therapy. Initial estimates of testing effects were derived from a recently completed randomized controlled trial (n = 200). Healthcare cost ($US, year 2007 values) and health-state utility data were obtained from the literature. The perspective was that of a US third-party payer. Probabilistic and one-way sensitivity analyses were performed to explore the range of plausible results.

RESULTS

The policy model included thromboembolic events (TEs) and bleeding events and was populated by data from the COUMAGEN trial. The rate of bleeding calculated for standard care approximated bleeding rates found in an independent cohort of warfarin patients. According to our model, pharmacogenomic testing provided an absolute reduction in the incidence of bleeds of 0.17%, but an absolute increase in the incidence of TEs of 0.03%. The improvement in QALYs was small, 0.003, with an increase in total cost of $US162 (year 2007 values). The incremental cost-effectiveness ratio (ICER) ranged from testing dominating to standard care dominating, and the ICER was <$US50,000 per QALY in 46% of simulations. Results were most sensitive to the cost of genotyping and the effect of genotyping.

CONCLUSION

Our model, based on initial clinical studies to date, suggests that warfarin pharmacogenomic testing may provide a small clinical benefit with significant uncertainty in economic value. Given the uncertainty in the analysis, further updates will be important as additional clinical data become available.

Randomized controlled trial of supervised patient self-testing of warfarin therapy using an internet-based expert system

BACKGROUND

Increased frequency of prothrombin time testing, facilitated by patient self-testing (PST) of the International Normalized Ratio (INR) can improve the clinical outcomes of oral anticoagulation therapy (OAT). However, oversight of this type of management is often difficult and time-consuming for healthcare professionals. This study reports the first randomized controlled trial of an automated direct-to-patient expert system, enabling remote and effective management of patients on OAT.

METHODS

A prospective, randomized controlled cross-over study was performed to test the hypothesis that supervised PST using an internet-based, direct-to-patient expert system could provide improved anticoagulation control as compared with that provided by an anticoagulation management service (AMS). During the 6 months of supervised PST, patients measured their INR at home using a portable meter and entered this result, along with other information, onto the internet web page. Patients received instant feedback from the system as to what dose to take and when the next test was due. During the routine care arm, patients attended the AMS at least every 4-6 weeks and were dosed by the anticoagulation pharmacist or physician. The primary outcome variable was the difference in the time in therapeutic range (TTR) between both arms.

RESULTS

One hundred and sixty-two patients were enrolled (male 61.6%, mean age 58.7 years), and 132 patients (81.5%) completed both arms. TTR was significantly higher during PST management than during AMS management (median TTR 74% vs 58.6%; z=5.67, P < 0.001).

CONCLUSIONS

The use of an internet-based, direct-to-patient expert system for the management of PST improves the control of OAT as compared with AMS management.

Achieved anticoagulation vs prosthesis selection for mitral mechanical valve replacement: a population-based outcome study

BACKGROUND

Thromboembolic events (TEs) are frequent after mechanical mitral valve replacement (MVR), but their association to anticoagulation quality is unclear and has never been studied in a population-based setting with patients who have a complete anticoagulation record.

METHODS

We compiled a complete record of all residents of Olmsted County, MN, who underwent mechanical MVR between 1981 and 2004, for all TE, bleeding episodes, and international normalized ratios (INRs) measured from prosthesis implantation.

RESULTS

In the 112 residents (mean [+/- SD] age, 57 +/- 16 years; 60% female residents) who underwent mechanical MVR, 19,647 INR samples were obtained. While INR averaged 3.02 +/- 0.57, almost 40% of INRs were < 2 or > 4.5. Thirty-four TEs and 28 bleeding episodes occurred during a mean duration of 8.2 +/- 6.1 years of follow-up. There was no trend of association of INR (average, SD, growth variance rate, or intensity-specific incidence of events) with TE. Previous cardiac surgery (p = 0.014) and ball prosthesis (hazard ratio [HR], 2.92; 95% CI, 1.43 to 5.94; p = 0.003) independently determined TE. With MVR using a ball prosthesis, despite higher anticoagulation intensity (p = 0.002), the 8-year rate of freedom from TE was considerably lower (50 +/- 9% vs 81 +/- 5%, respectively; p < 0.0001). Compared with expected stroke rates in the population, stroke risk was elevated with non-ball prosthesis MVR (HR 2.6; 95% CI, 1.3 to 5.2; p = 0.007) but was considerable with ball prosthesis MVR (HR 11.7; 95% CI, 7.5 to 18.4; p < 0.0001). INR variability (SD) was higher with a higher mean INR value (p < 0.0001). INR variability (HR 2.485; 95% CI, 1.11 to 5.55; p = 0.027) and cancer history (p < 0.0001) independently determined bleeding rates.

CONCLUSION

This population-based comprehensive study of anticoagulation and TE post-MVR shows that, in these closely anticoagulated patients, anticoagulation intensity was highly variable and not associated with TE incidence post-MVR. Higher anticoagulation intensity is linked to higher variability and, thus, to bleeding. The MVR-ball prosthesis design is associated with higher TE rates notwithstanding higher anticoagulation intensity, and its use should be retired worldwide.

Outcomes and predictors of very stable INR control during chronic anticoagulation therapy

For patients on warfarin therapy, an international normalized ratio (INR) recall interval not exceeding 4 weeks has traditionally been recommended. Less frequent INR monitoring may be feasible in stable patients. We sought to identify patients with stable INRs (defined as having INR values exclusively within the INR range) and comparator patients (defined as at least one INR outside the INR range) in a retrospective, longitudinal cohort study. Occurrences of thromboembolism, bleeding, and death were compared between groups. Multivariate logistic regression models were used to identify independent predictors of stable INR control. There were 2504 stable and 3569 comparator patients. The combined rates of bleeding and thromboembolism were significantly lower in stable patients. Independent predictors of stable INR control were age older than 70 years and the absence of comorbid heart failure and diabetes. Stable patients were significantly less likely to have target INR of 3.0 or higher or chronic diseases. We hypothesize that many patients demonstrating stable INR control could be safely treated with INR recall intervals greater than the traditional 4 weeks.

INR variability in atrial fibrillation: a risk model for cerebrovascular events

BACKGROUND

Use of vitamin K antagonists (VKAs) for stroke prophylaxis in patients with non-valvular atrial fibrillation (NVAF) necessitates frequent monitoring of the international normalized ratio (INR) to avoid the increased risk of hemorrhage associated with excess anticoagulation, or ischemic stroke due to insufficient anticoagulation. We therefore developed a model to estimate the excess morbidity attributable to inadequate INR control in NVAF populations.

METHODS

Equations expressing the risk of cerebrovascular events as a function of INR were generated using published data. Additional functions were developed to estimate the excess risk attributable to inferior INR control, using the clinical trial setting as the reference.

RESULTS

The derived risk functions were applied to French NVAF patients receiving anticoagulation in routine medical practice. This population achieved a time in therapeutic range (INR 2.0-3.0) of 59%, compared with 68% time in therapeutic range (TTR) in the SPORTIF III and V clinical trials. However, there was considerable variation in the TTR among patients in routine care, of whom 36% were in range for less than 50% of the time. Among this latter group, the relative risk, compared with the clinical trial setting, was 1.47 for ischemic stroke and 2.68 for intracranial hemorrhage. Conversely, for patients achieving a TTR greater than 50%, the relative risks for ischemic stroke and intracranial hemorrhage were 0.99 and 1.16, respectively.

CONCLUSIONS

This model permits estimation of the excess risk attributable to inferior INR control in NVAF populations receiving VKA anticoagulation, and has implications for public health planning and management.

Comparison of INR stability between self-monitoring and standard laboratory method: preliminary results of a prospective study in 67 mechanical heart valve patients

INTRODUCTION

Thromboembolic accidents and haemorrhage are the main complications observed during long-term follow-up of mechanical heart valve patients. Several suggestions for improving anticoagulation quality have been made, including international normalised ratio (INR) self-monitoring.

OBJECTIVES

We report the preliminary results of a single-centre, open, randomised study (scheduled population of 200 patients), which compares monthly laboratory monitoring (group A) versus weekly self-monitoring of INR (group B). The primary aim is INR stability improvement within the target range, and the secondary aim is adverse events reduction.

PATIENTS AND METHODS

Between May 2004 and June 2005, 67 patients with an average age of 56.6 years (+/-9.6), were enrolled in the study (group A: 34 patients, group B: 33 patients). The mean follow-up was 47 weeks (+/-11.5). The two groups differed only in the sex ratio (44.1 and 21.2% of women in groups A and B respectively, p=0.0459). Mechanical heart valves were aortic in 73% of patients, mitral in 13.5%, and multiple in 13.5%. Sixty-five patients (97%) were treated with fluindione, the others with acenocoumarol. The intraclass correlation coefficient between the self- and laboratory-monitored INR was 0.75.

RESULTS

The time spent in the INR target range (group A: 53+/-19%, group B: 57+/--19%, p=0.45) and the time spent in the INR therapeutic range, between 2 and 4.5, (group A: 86+/-14%, group B: 91+/-7%, p=0.07) are longer in group B, but not significantly so. For patients outside the range, the absolute mean deviation of INR from the target or therapeutic range (range standardized between 0 and 100) is lower for the self-monitoring group (41.1+/-39.3 and 11.27+/-11.2) than for the control group (62.4+/-72.6 and 39.2+/-52.8). This difference is significant (p=0.0004 and p=0.0005). Eighteen adverse events were reported: 17 haemorrhages, 13 in group A (9 mild, 4 serious) and four in group B (all mild), and one sudden death in group B, two days after the patient's discharge. No thromboembolic events were reported. Six patients (8.8 %), 3 in each group, dropped out of the study.

CONCLUSION

This first study evaluating INR self-monitoring in France shows that this method leads to better stability of the INR within the target range. On the basis of these preliminary data, this appears to be related to a decrease in serious haemorrhages (11.8% serious haemorrhage cases in group A versus 0% in group B, p=0.06, NS).

Quality of oral anticoagulant therapy in patients who perform self management: warfarin versus phenprocoumon

BACKGROUND

The quality of oral anticoagulant therapy may be related to which type of coumarin is used. The aim was to investigate whether phenprocoumon or warfarin provide the highest quality of oral anticoagulant therapy in patients who manage the therapy themselves.

METHODS AND RESULTS

In a cohort study 519 patients on self managed oral anticoagulant therapy were included. Quality control parameters, were, the percentage of time spent in the therapeutic range and the variability in the patients' INR values. Time within therapeutic INR target range in the patient group treated respectively with warfarin and phenprocoumon was 70.2% and 74.0% (P = 0.008).The median variance in the warfarin group was 0.35 (95% CI (0.32-0.38)) and 0.29 (95% CI (0.25-0.33)) in the phenprocoumon group (P = 0.0004).

CONCLUSION

Phenprocoumon provides a higher percentage of time spent in therapeutic INR interval and a lower variation of INR-values compared with warfarin.

KIDCLOT: the importance of validated educational intervention for optimal long term warfarin management in children

BACKGROUND

Advances in medical and surgical therapy in children have resulted in increased survival in children with primary illnesses. However, thrombosis is a serious complication of this success and results in mortality and morbidity. Prevention or treatment of thrombosis using warfarin is challenging in children due to its narrow therapeutic index and the unique differences in children, including variable nutritional intake and the occurrence of common concomitant viral or bacterial illnesses which alter warfarin metabolism. The variable response to warfarin in children necessitates frequent International Normalized Ratio (INR) monitoring. Education may improve time in therapeutic range (TTR) a measure of warfarin effect, and a surrogate for patient adherence, safety and efficacy.

METHODS

The Pediatric Anticoagulation program (Stollery Children's Hospital) developed a novel child-focused educational program KIDCLOT-POC about warfarin therapy and POC-INR meter use. A total of twenty eight children, and their caregivers, participated in KIDCLOT-POC. Questionnaire score comparisons and practical demonstrations assessed the learners' theoretical and practical knowledge of warfarin management.

RESULTS

In caregivers, the median pre, post and knowledge retention questionnaire scores were 50 (IQR 27), 93 (IQR 6) (p<0.0001) and 96 (IQR 6) (p<0.0001), respectively. In the 18 children who were >or=6 years of age, post and knowledge retention questionnaire scores were 90 (IQR 16) and 92 (IQR 23) (p=0.44), respectively. The TTR for all children was 81.7% (SD 13.1).

CONCLUSIONS

Implementation of KIDCLOT-POC program appears to promote high knowledge development and retention in children and caregivers and high TTR with no adverse events.

Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). It describes the antithrombotic effect of the VKAs, the monitoring of anticoagulation intensity, and the clinical applications of VKA therapy and provides specific management recommendations. Grade 1 recommendations are strong and indicate that the benefits do or do not outweigh the risks, burdens, and costs. Grade 2 recommendations suggest that the individual patient's values may lead to different choices. (For a full understanding of the grading, see the "Grades of Recommendation" chapter by Guyatt et al, CHEST 2008; 133:123S-131S.) Among the key recommendations in this article are the following: for dosing of VKAs, we recommend the initiation of oral anticoagulation therapy, with doses between 5 mg and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 1B); we suggest against pharmacogenetic-based dosing until randomized data indicate that it is beneficial (Grade 2C); and in elderly and other patient subgroups who are debilitated or malnourished, we recommend a starting dose of < or = 5 mg (Grade 1C). The article also includes several specific recommendations for the management of patients with nontherapeutic INRs, with INRs above the therapeutic range, and with bleeding whether the INR is therapeutic or elevated. For the use of vitamin K to reverse a mildly elevated INR, we recommend oral rather than subcutaneous administration (Grade 1A). For patients with life-threatening bleeding or intracranial hemorrhage, we recommend the use of prothrombin complex concentrates or recombinant factor VIIa to immediately reverse the INR (Grade 1C). For most patients who have a lupus inhibitor, we recommend a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 1A]. We recommend that physicians who manage oral anticoagulation therapy do so in a systematic and coordinated fashion, incorporating patient education, systematic INR testing, tracking, follow-up, and good patient communication of results and dose adjustments [Grade 1B]. In patients who are suitably selected and trained, patient self-testing or patient self-management of dosing are effective alternative treatment models that result in improved quality of anticoagulation management, with greater time in the therapeutic range and fewer adverse events. Patient self-monitoring or self-management, however, is a choice made by patients and physicians that depends on many factors. We suggest that such therapeutic management be implemented where suitable (Grade 2B).

Quality of anticoagulation and use of warfarin-interacting medications in long-term care: a chart review

BACKGROUND

Maintenance of therapeutic International Normalized Ratio (INR) in the community is generally poor. The supervised environment in long-term care facilities may represent a more ideal setting for warfarin therapy since laboratory monitoring, compliance, dose adjustment, and interacting medications can all be monitored and controlled. The objectives of this study were to determine how effectively warfarin was administered to a cohort of residents in long-term care facilities, to identify the proportion of residents prescribed warfarin-interacting drugs and to ascertain factors associated with poor INR control.

METHODS

A chart review of 105 residents receiving warfarin therapy in five long-term care facilities in Hamilton, Ontario was performed. Data were collected on INR levels, warfarin prescribing and monitoring practices, and use of interacting medications.

RESULTS

Over a 12 month period (28,555 resident-days, 78.2 resident years) 3065 INR values were available. Residents were within, below and above the therapeutic range 54%, 35% and 11% of the time, respectively. Seventy-nine percent of residents were prescribed at least one warfarin-interacting medication during the period in review. Residents receiving interacting medications spent less time in the therapeutic range (53.0% vs. 58.2%, OR = 0.93, 95% confidence interval 0.88 to 0.97, P = 0.002). Adequacy of anticoagulation varied significantly between physicians (time in therapeutic range 45.9 to 63.9%).

CONCLUSION

In this group of long-term care residents, warfarin control was suboptimal. Both prescriber and co-prescription of interacting medications were associated with poorer INR control. Future studies should seek strategies to improve prescriber skill and decrease use of interacting medications.

Is long-term pharmacist-managed anticoagulation service efficient? A pragmatic randomized controlled trial

BACKGROUND

Some pharmacist-managed anticoagulation services (PMAS) provide initial follow-up to patients on oral anticoagulant, who are transferred to their physician once they are stabilized. This may be as effective as and less expensive than long-term PMAS follow-up.

METHODS

Once PMAS patients were stabilized and ready for discharge, they were randomized to be transferred to their physician or stay with the PMAS. Quality of international normalized ratio (INR) control, incidence of complications, health-related quality of life, use of health care services, and direct incremental cost of PMAS follow-up were evaluated.

RESULTS

One hundred thirty-eight physicians and 250 patients participated. Patients were initially followed at the PMAS for a mean of 11.3 weeks and afterwards were followed by their physician (n = 122) or by the PMAS pharmacists (n = 128) for a mean of 14.9 and 14.5 weeks, respectively. Pharmacist-managed anticoagulation services' and physician's patients were within the exact target range 77.3% and 76.7% of the time (95% CI of the difference -4.9% to 6.0%) and within the extended range 93.0% and 91.6% of the time (95% CI -2.1% to 4.7%), respectively. Pharmacist-managed anticoagulation services patients have seen their family physician less often (95% CI -3.1 to -0.1 visit per year). Number of INR tests, incidence of complications, and health-related quality of life were similar in both groups. The incremental cost of PMAS follow-up was estimated at CAN$123.80 per patient year.

CONCLUSION

Once PMAS patients are well stabilized, maintaining a PMAS follow-up or transferring them to their physician is associated with excellent INR control. However, long-term PMAS follow-up may be more expensive.

In-patient international normalized ratio self-testing instruction after mechanical heart valve implantation

BACKGROUND

Patient self-testing of the international normalized ratio (INR) has been shown to improve management of anticoagulation with warfarin and reduce risks of thromboembolism and bleeding. Self-testing instruction usually begins several weeks after hospital discharge. We evaluated the feasibility of in-hospital INR self-testing instruction in patients recovering from valve replacement.

METHODS

We instituted an education program on a self-testing device before hospital discharge in 50 adult patients (median age, 54 years; 66% men) undergoing cardiac valve replacement with mechanical prostheses. Patients were monitored for 1 month to assess their ability to self-test and the accuracy of the INR measurements.

RESULTS

Self-testing instruction began on postoperative day 4 (range, 1 to 8 days). Each patient had an average of 3.5 teaching sessions; each session lasted approximately 20 minutes. One month after discharge, all patients (98%) but 1 were able to self-test. No patient required interval instruction. One bleeding episode occurred in a patient whose INR exceeded the therapeutic range. Once warfarin doses were stabilized, 5 patients had subtherapeutic INR values on self-testing. The mean INR test result obtained from the coagulometer correlated well with values obtained by laboratory determination (r = 0.79).

CONCLUSIONS

This evaluation of an in-hospital education program demonstrates that patients are able to learn INR self-testing and that most will continue to use the method without the need for interval instruction. Improved anticoagulation management by early introduction of INR self-testing should reduce thromboembolic and hemorrhagic complications after valve replacement.

Effect of setting, monitoring intensity and patient experience on anticoagulation control: a systematic review and meta-analysis of the literature

OBJECTIVES

To investigate the relationship between time spent in the recommended target International Normalised Ratio (INR) range and the setting and intensity of anti coagulant monitoring, in both treatment-experienced and treatment-naive atrial fibrillation (AF) patients receiving oral anticoagulation (OAC) therapy for the prevention of ischaemic stroke.

RESEARCH DESIGN AND METHODS

Systematic review of published studies on participants with atrial fibrillation on anticoagulation therapy. We compared frequent monitoring (well-controlled, according to a strict protocol) versus infrequent monitoring (frequency representative of routine clinical practice), specialised care versus usual care, and naive versus prior anticoagulant use. Meta-analysis was performed using a random effects model.

RESULTS

36 studies were included, 22 (primary data) of AF patients managed in line with the consensus guidelines target INR range of 2.0-3.0, and 14 studies (secondary data) of mixed patient groups, including AF, with an INR target of 2.0-3.5. Both data sets were combined for sensitivity analysis. Pooled mean time in INR range was 59.1% (95% CI: 55.5, 62.8%) and 64.3% (95% CI: 60.5, 68.0%) for infrequent monitoring and frequent monitoring, respectively. Significantly more time was spent in range in specialist care settings compared to usual care: +11.3% (95% CI: 0.1-21.7%). Naive OAC users spent less time in range 56.5% (95% CI: 45.5-67.5%) than existing users 61.2% (95% CI: 57.2-65.2%). All of these differences were found to be significant in the sensitivity analyses.

CONCLUSIONS

INR control is variable and dependent on monitoring intensity and duration of anticoagulant therapy.

[Self-monitoring of oral coagulation: for which patients?]

Oral anticoagulant treatment with vitamin K antagonists (VKA) is prescribed to an increasing number of patients. These drugs are,however, one of the leading causes of iatrogenic disease. It is essential to monitor the intensity of anticoagulation very closely, by a biological measure (INR, international normalized ratio),to minimize the frequency of thrombotic and hemorrhagic events that may occur in the case of insufficient or excessive anticoagulation. Current methods of monitoring INR can be improved.Self-testing of INR and self-monitoring of oral coagulation treatment offer advantages over more conventional approaches. This self-testing can be performed by most patients capable of living alone, regardless of their social status or educational level. Despite the existence of very reliable self-testing devices, France is very far behind in the use of these instruments that allow management and improve the morbidity and mortality inherent in anticoagulant treatment.

Outpatient management of oral vitamin K antagonist therapy: defining and measuring high-quality management

Oral anticoagulation therapy with warfarin is the mainstay of prevention and treatment of thromboembolic disease. However, it remains one of the leading causes of harmful medication errors and medication-related adverse events. The beneficial outcomes of oral anticoagulation therapy are directly dependent upon the quality of dose and anticoagulation management, but the literature is not robust with regards to what constitutes such management. This review focuses on, and attempts to define, the parameters of high-quality anticoagulation management and identifies the appropriate outcome measures constituting high-quality management. Elements discussed include the most fundamental measure, time in therapeutic range, along with other parameters including therapy initiation, time to therapeutic range, dosing management when patients are not in therapeutic range, perioperative dosing management, patient education, and other important outcome measures. Healthcare providers who manage oral anticoagulation therapy should utilize these parameters as a measure of their performance in an effort to achieve high-quality anticoagulation management.

A visual medication schedule to improve anticoagulation control: a randomized, controlled trial

BACKGROUND

Misunderstanding between clinicians and patients may lead to medication-related errors and poor clinical outcomes, particularly in anticoagulant care.

METHODS

One hundred forty-seven chronic warfarin users were randomized to receive a visual medication schedule at each visit, along with brief counseling, versus standard care, and followed for 90 days. At baseline, patient and clinician reports of the prescribed warfarin regimen were recorded to identify patients as "discordant" versus "concordant" to determine whether the effect of the intervention varied with clinician-patient discordance.

RESULTS

At baseline, clinician-patient warfarin regimen discordance was common in intervention and control groups (38% versus 42%). Intervention subjects achieved anticoagulation control more rapidly than control subjects (median 28 versus 42 days; hazard ratio [HR], 1.43; confidence interval [CI], 1.00, 2.06). The benefit of the intervention was significant among subjects with baseline regimen discordance (median, 28 versus 49 days; HR, 1.92; CI, 1.08, 3.39) but not among subjects with baseline concordance (median 28 versus 35 days; HR, 1.14; CI, 0.71,1.83).

DISCUSSION

Among patients in poor anticoagulant control whose understanding of their warfarin regimen is discordant with their providers', a visual medication schedule, combined with brief counseling, reduced time to anticoagulation control. The study suggests a simple strategy to enhance medication safety and efficacy for at-risk patients.

Quality of clinical documentation and anticoagulation control in patients with chronic nonvalvular atrial fibrillation in routine medical care

OBJECTIVE

Anticoagulation quality and record documentation were retrospectively assessed in patients with chronic nonvalvular atrial fibrillation (CNVAF) managed in a routine care setting.

METHODS

Medical record data extraction from physician practices in 4 regions of the United States.

RESULTS

Of 686 patients, 59% had an electrocardiogram confirming CNVAF, 84% listed at least 1 stroke risk factor, and 60% indicated the goal target international normalized ratio (INR). Two thirds of INRs>3.0 or <2.0 had no recorded dose change, nor did 45% of INRs>5.0. Vitamin K was given (3%) or anticoagulation was temporarily discontinued (9%) for INRs>5.0. The median interval of INR testing was 21 days, which decreased to 7 days for INRs> 4.60. Patients spent 58% of the time in therapeutic range.

CONCLUSION

Serious deficiencies in quality and documentation of routine medical care of anticoagulation for patients with CNVAF continue to exist.

Direct-to-patient expert system and home INR monitoring improves control of oral anticoagulation

BACKGROUND AND OBJECTIVE

Internet-based disease management programs have the potential to improve patient care. The objective of this study was to determine whether an interactive, internet-based system enabling supervised, patient self-management of oral anticoagulant therapy provided management comparable to an established anticoagulation clinic.

PATIENTS/METHODS

Sixty patients receiving chronic oral anticoagulant therapy who had access to the internet and a printer, were enrolled into this prospective, single-group, before-after study from a single clinic and managed between March 2002 and January 2003. Patients learned how to use a home prothrombin time monitor and how to access the system through the internet. Patients used the system for six months, with daily review by the supervising physician. The primary outcome variable was the difference in time in therapeutic range prior to and following introduction of internet-supervised patient self-management.

RESULTS

The mean time in therapeutic range increased from 63% in the anticoagulation clinic (control period) to 74.4% during internet-supervised patient self-management (study period). The mean difference score between control and study periods was 11.4% (P = 0.004, 95% confidence interval 5.5-17.3%). There were no hemorrhagic or thromboembolic complications.

CONCLUSIONS

This novel approach of internet-supervised patient self-management improved time in therapeutic range compared to an anticoagulation clinic. This is the first demonstration of an internet-based expert system enabling remote and effective management of patients on oral anticoagulants. Expert systems may be applicable for management of other chronic diseases.

Self-management of oral anticoagulant therapy: A systematic review and meta-analysis

BACKGROUND

A number of randomized controlled trials have compared self-management of oral anticoagulant therapy with conventional management. However, the results have not appeared consistent and a systematic review and meta-analysis are therefore needed in order to evaluate self-management of oral anticoagulant therapy. The aim of this study was to evaluate the efficacy and safety of self-management of oral anticoagulant therapy for patients on long-term oral anticoagulant therapy.

METHODS

A systematic review and meta-analysis including randomized controlled trials with highly selected patients comparing self-management of oral anticoagulant therapy with conventional treatment. Data were extracted in terms of study characteristics, quality of trials and outcome (death, minor and major complications (thromboembolic and bleeding events), and time within therapeutic INR target range).

RESULTS

Ten trials with a total of 2724 patients were included. Two of the trials could be classified as high quality trials. Considering all trials, self-management was associated with a reduced risk of death (relative risk (RR)=0.48, 95% confidence interval (CI) 0.29-0.79, p=0.004), major complications (RR=0.58, 95% CI 0.42-0.81, p=0.001) and with increasing time within therapeutic INR target range (weighted mean difference=6.53, 95% CI 2.24-10.82, p=0.003). No clear effect was found regarding minor complications (RR=0.98, 95% CI 0.49-1.99, p=0.96).

CONCLUSIONS

A majority of the existing trials have various methodological problems. However, self-management of oral anticoagulant therapy appeared at least as good and possible better than conventional management in highly selected patients.

The effect of hospitalization on oral anticoagulation control: A population-based study

BACKGROUND

For patients taking oral anticoagulants (OAC), the proportion of time spent in the therapeutic range is strongly associated with bleeding and thromboembolic risk. Previous studies examining OAC control may not generalize because the patient population was select or INR capture was incomplete.

OBJECTIVES

Measure OAC control for an entire population of elderly people and determine patient factors associated with OAC control.

PATIENTS

People in Eastern Ontario without valve replacement aged 65 years or greater who were treated with warfarin between 1 September 1999 and 1 September 2000.

DESIGN

Retrospective cohort study using population-based administrative databases. OAC control was measured as the proportion of days in therapeutic range (PDTR), defined as the number days with the INR between 2 and 3 divided by total number of days observation. Linear interpolation was used to determine INR levels between measures. Negative binomial regression was used to identify patient factors independently associated with PDTR. We also determined which factors were associated with proportion of days with a critically low (<1.5) or critically high (>/=5) INR.

RESULTS

7179 people were followed for a total of 3238 years. 15% of people were hospitalized during the study. Overall, PDTR was 59.2% (95% CI 59.1%-59.2%). Independent of all other significant factors, hospitalization was associated with a 15% decrease in the PDTR 15% (rate ratio 0.85, 95% CI 0.83-0.87). Hospitalization was also independently associated with greater proportion of time with a critically low INR (rate ratio 1.68, 95% CI 1.51-1.88) and a critically high INR (1.70, 95% CI 1.38-2.08).

CONCLUSIONS

Elderly people in eastern Ontario taking warfarin were therapeutic 59.2% of the time. Independent of other patient factors, patients who are hospitalized have the greatest risk of poor anticoagulation control. Control for anticoagulated patients who get hospitalized should be reviewed to determine if and how it could be improved.

The interval between prothrombin time tests and the quality of oral anticoagulants treatment in patients with chronic atrial fibrillation

BACKGROUND

The incidence of stroke in patients with atrial fibrillation (AF) can be significantly reduced with warfarin therapy especially if optimally controlled.

OBJECTIVES

To evaluate the effect of the interval between consecutive prothrombin time measurements on the time in therapeutic range (INR 2-3) in a cohort of patients with AF on chronic warfarin treatment in the community.

METHODS

All INR measurements available from a relatively large cohort of patients with chronic AF were reviewed and the mean interval between consecutive INR tests of each patient was correlated with the time in therapeutic range (TTR).

RESULTS

Altogether 251,916 INR measurements performed in 4408 patients over a period of seven years were reviewed. Sixty percent of patients had their INR measured on average every 2 to 3 weeks and most others were followed at intervals of 4 weeks or longer. A small proportion (3.6%) had their INR measured on average every week. A significant decline in the time in therapeutic range was observed as the intervals between tests increased. At one to three weeks interval the TTR was 48%, at 4 weeks interval 45% and at 5 weeks 41% (P<0.0005). A five percent increment in TTR was observed if more tests were performed at multiplications of exactly 7 days (43% vs 48% P<0.0001).

CONCLUSIONS

A better control with an increase in the TTR was observed in patients with atrial fibrillation if prothrombin time tests are performed at regular intervals of no longer than 3 weeks.

The importance of establishing regimen concordance in preventing medication errors in anticoagulant care

Miscommunication between patients and providers can have serious consequences, especially where medications are concerned. We examined whether regimen discordance between patient and provider, a possible result of miscommunication, contributes to unsafe medication management. We studied 220 patients taking warfarin in an anticoagulation clinic to characterize two medication assessment methods. We measured (1) adherence by asking patients to report any missed doses and (2) concordance between patients' and providers' reports of warfarin regimens. We categorized patients as having regimen adherence if they missed no doses, and concordance if there was patient-provider agreement in weekly dosage. We characterized anticoagulant outcomes as unsafe if international normalized ratio (INR) values were <2.0 (at risk for thrombosis) or >4.0 (at risk for hemorrhage), and explored relationships among adherence, concordance, and anticoagulant outcomes. One hundred fifty-five patients (71%) reported no missed doses during the prior 30 days. Poor adherence was associated with underanticoagulation (AOR 2.33, 1.56-3.45), but not overanticoagulation (AOR 1.36, 0.69-2.66). One hundred ten patients (50%) reported regimens discordant with clinicians' report. There was no relationship between patients' reports of adherence and concordance. Among adherent patients, discordance was associated with underanticoagulation (AOR 1.67, 1.00-2.78) and overanticoagulation (AOR 3.44, 1.32-9.09). Discordance regarding warfarin regimens is common and places patients at risk for adverse events. To promote safe and effective care, clinicians should separately determine adherence and regimen concordance during routine medication assessments. Systems need to be developed to ensure concordance in medication regimens.

Cost-effectiveness of self-managed versus physician-managed oral anticoagulation therapy

BACKGROUND

Patient self-management of long-term oral anticoagulation therapy is an effective strategy in a number of clinical situations, but it is currently not a funded option in the Canadian health care system. We sought to compare the incremental cost and health benefits of self-management with those of physician management from the perspective of the Canadian health care payer over a 5-year period.

METHODS

We developed a Bayesian Markov model comparing the costs and quality-adjusted life years (QALYs) accrued to patients receiving oral anticoagulation therapy through self-management or physician management for atrial fibrillation or for a mechanical heart valve. Five health states were defined: no events, minor hemorrhagic events, major hemorrhagic events, thrombotic events and death. Data from published literature were used for transition probabilities. Canadian 2003 costs were used, and utility estimates were obtained from various published sources.

RESULTS

Self-management resulted in 3.50 fewer thrombotic events, 0.78 fewer major hemorrhagic events and 0.12 fewer deaths per 100 patients than physician management. The average discounted incremental cost of self-management over physician management was found to be 989 dollars (95% confidence interval [CI] 310 dollars-1655 dollars) per patient and the incremental QALYs gained was 0.07 (95% CI 0.06-0.08). The cost-effectiveness of self-management was 14,129 dollars per QALY gained. There was a 95% chance that self-management would be cost-effective at a willingness to pay of 23,800 dollars per QALY. Results were robust in probabilistic and deterministic sensitivity analyses.

INTERPRETATION

This model suggests that self-management is a cost-effective strategy for those receiving long-term oral anticoagulation therapy for atrial fibrillation or for a mechanical heart valve.

Effect of Study Setting on Anticoagulation Control

BACKGROUND

For patients receiving therapy with oral anticoagulants (OACs), the proportion of time spent in the therapeutic range (ie, anticoagulation control) is strongly associated with bleeding and thromboembolic risk. The effect of study-level factors, especially study setting, on anticoagulation control is unknown.

OBJECTIVES

Describe anticoagulation control achieved in the published literature. We also used metaregressive techniques to determine which study-level factors significantly influenced anticoagulation control.

STUDIES

All published randomized or cohort studies that measured international normalized ratios (INRs) serially in anticoagulated patients and reported the proportion of time between INRs ranging from 1.8 to 2.0 and 3.0 to 3.5.

RESULTS

We identified 67 studies with 123 patient groups having 50,208 patients followed for a total of 57,154.7 patient-years. A total of 68.3% of groups were from anticoagulation clinics, 7.3% were from clinical trials, and 24.4% were from community practices. Overall, patients were therapeutic 63.6% of time (95% confidence interval [CI], 61.6 to 65.6). In the metaregression model, study setting had the greatest effect on anticoagulation control with studies in community practices having significantly lower control than either anticoagulation clinics or clinical trials (-12.2%; 95% CI, -19.5 to -4.8; p < 0.0001). Self-management was associated with a significant improvement of time spent in the therapeutic range (+7.0%; 95% CI, 0.7 to 13.3; p = 0.03).

CONCLUSIONS

Patients who have received anticoagulation therapy spend a significant proportion of their time with an INR out of the therapeutic range. Patients from community practices showed significantly worse anticoagulation control than those from anticoagulation clinics or clinical trials. This should be considered when interpreting the results of, and generalizing from, studies involving OACs.

Differential associations of beta-blockers with hemorrhagic events for chronic heart failure patients on warfarin

PURPOSE

Beta-blockers have many different physiologic effects that could potentially influence the risk of hemorrhagic events in chronic heart failure patients (CHF) on warfarin. We examined how different beta-blockers vary in their associated risk of a hemorrhagic event.

METHODS

We used databases from the Department of Veterans Affairs (VA) that contain information on medications prescribed, diagnoses, and hospitalizations. We identified patients with CHF on warfarin and either metoprolol, carvedilol, atenolol, or no beta-blocker during 1999-2001. We modeled time to first hemorrhagic event using a Cox proportional hazards model, adjusting for age, ethnicity, comorbidities, and other factors. INR levels were examined in a subsample of 3546 patients.

RESULTS

We identified 66,988 CHF patients on warfarin. Hemorrhagic events occurred in 15.3% of the sample and, in 3.8% of the sample, the hemorrhage was considered severe. Compared to patients on carvedilol, the hazards ratio for a new hemorrhagic event was 1.25 (1.17, 1.34) for no beta-blocker, 1.27 (1.18, 1.38) for atenolol, and 1.38 (1.28, 1.48) for metoprolol. No differences in INR levels were evident among the four groups.

CONCLUSIONS

The risk for a hemorrhagic event among CHF patients on warfarin may be affected by beta-blocker use and varies depending on which beta-blocker is prescribed.

Point-of-care antithrombotic monitoring in children

INTRODUCTION

The use of oral anticoagulant therapy is increasing in children. Managing anticoagulant therapy in children presents unique challenges, including poor venous access. The advent of point-of-care (POC) monitoring of anticoagulant therapy offers a potential solution to this challenge. This paper reviews the published literature relating to POC monitoring of oral anticoagulant therapy in children.

MATERIALS AND METHODS

A Medline search was conducted and identified key publications. Papers were reviewed with respect to their objectives, populations and POC device investigated. Study limitations were identified.

RESULTS

Five publications and one abstract were identified, reporting studies using five different POC monitors. Three studies had a strong clinical management focus. Outcome measures assessed included target therapeutic range achievement and frequency of adverse events. Correlation between POC and laboratory-based results ranged from 0.83 to 0.96. Home monitoring and self-management using POC monitors were both reported to be preferred compared to standard laboratory testing.

CONCLUSIONS

POC monitoring of oral anticoagulant therapy in children offers considerable advantages. The reviewed literature would suggest such monitoring can be performed accurately and reliably. The impact of quality control issues, such as calibration of thromboplastin ISI in POC devices, has not been explored in a paediatric population. Further studies are needed to clarify such issues and confirm the safety, reliability and efficacy of POC monitoring of oral anticoagulant therapy in children, including its home monitoring and self-management programs.

Optimal INR for prevention of stroke and death in atrial fibrillation: a critical appraisal

INTRODUCTION

Patients with nonvalvular atrial fibrillation are at increased risk for systemic embolism, predominantly disabling stroke. To study how stroke and mortality rates vary with different degrees of anticoagulation reflected by the international normalised ratio (INR) we critically assess information from different sources.

MATERIALS AND METHODS

1. Computerized search of the medical literature published between 1980 and July 2004 was performed using MEDLINE applied to various combinations of the search terms of atrial fibrillation, warfarin, anticoagulation, anticoagulation intensity, and INR, not restricted by language. 2. We performed a record linkage analysis with death hazard estimated as a continuous function of INR based on 21,967 patients. Similarly the risk of admission to hospital or death due to diseases of the vessels of the brain was estimated. 3. Re-analysis of data earlier published by Hylek et al. from year 2003.

RESULTS AND CONCLUSIONS

1. One randomised study showed a significantly lower risk of stroke for mean INR 2.4 compared to mean INR 1.3 combined with aspirin. Remaining studies found INRs of 2-2.5 to be as efficacious as higher anticoagulation intensities.2. Mortality as well as risk of admission to hospital or death due to diseases of the vessels of the brain followed U-shaped curves with minimum at INR 2.2 and 2.4, respectively. At high INR the risk increased 2.3 times per 1 unit increase of INR for death and 1.7 times for events in the vessels of the brain.3. The re-analysing of data of Hylek et al. indicated that there might be a substantial increase of the risk of intracranial hemorrhage when INR is increased from 2.5 to 4. We conclude that INRs in the interval 2.0--2.5 give the lowest risk of stroke and death in patients with nonvalvular atrial fibrillation.

Search for Predictors of Nontherapeutic INR Results with Warfarin Therapy

BACKGROUND

The effectiveness and safety of warfarin require maintaining an international normalized ratio (INR) within the therapeutic range.

OBJECTIVE

To identify predictors of nontherapeutic INR results in patients receiving warfarin.

METHODS

A retrospective study was conducted using 350 ambulatory care patients from a broad geographic region, all receiving long-term warfarin therapy and followed in a tertiary-care cardiology clinic. Possible predictors of nontherapeutic INR results (gender, age, body weight, body mass index, height, race, tobacco use, alcohol use, warfarin dose, therapeutic indication, regimen intensity, INR monitoring frequency/category, interacting medications, adverse events) were assessed with logistic regression models. Subset analysis involved 146 patients concurrently monitored with capillary whole blood INR (CoaguChek).

RESULTS

As measured on venous specimens, 52% (182/350) of the patients had subtherapeutic INR results and 13% (44/350) had supratherapeutic INR results despite frequent (≤4 wk) monitoring in 75% of the patients. Due to the small sample size, supratherapeutic INR results could not be further analyzed. Of 19 predictors tested, only daily warfarin dose (p < 0.02) and regimen intensity (p < 0.03) were significant independent and additive predictors of subtherapeutic results. Patients on the high-intensity regimen (INR 2.5–3.5) and receiving warfarin ≤6 mg/day had >50% risk of having subtherapeutic INR results. Subtherapeutic CoaguChek results were independent predictors of subtherapeutic venipuncture INR results in the subset (p = 0.001).

CONCLUSIONS

In the absence of readily identifiable predictors, only higher warfarin dosing and/or more frequent monitoring (possibly with point-of-care/home monitoring devices) may minimize the time that INRs are subtherapeutic, especially in patients receiving low-dose and/or high-intensity anticoagulation therapy.