Semi-empirical anticoagulation model (SAM): INR monitoring during Warfarin therapy

The International Normalized Ratio (INR) monitoring is an essential component to manage thrombotic disease therapy. This study presents a semi-empirical model of INR as a function of time and assigned therapy (Warfarin, k-vitamin). With respect to other methodologies, this model is able to describe the INR using a limited number of parameters and is able to describe the time variation of INR described in the literature. The presented methodology showed great accuracy in model calibration [(trueness (precision)]: 0.2% (0.1%) to 1.2% (0.3%) for coagulation factors, from 5% (9%) to 9.7% (12%) for Warfarin-related parameters and 38% (40%) for K-vitamin-related parameters. The latter value was considered acceptable given the assumptions made in the model. It has two other important results: the first is that it was able to correctly estimate INR with respect to daily therapy doses taken from the literature. The second is that it introduces a single numeric semi-empirical parameter that is able to correlate INR/dose response to physiological and environmental condition of patients.

Upper-Extremity Deep-Vein Thrombosis: A Retrospective Cohort Evaluation of Thrombotic Risk Factors at a University Teaching Hospital Antithrombosis Clinic

BACKGROUND

Upper-extremity deep-vein thrombosis (UEDVT) causes significant morbidity and mortality and is not well characterized in the existing literature, particularly in underrepresented minorities such as African Americans.

OBJECTIVE

To describe the characteristics of a cohort of patients with UEDVT seen at an urban academic medical center.

METHODS

This was a retrospective cohort study among patients with a confirmed UEDVT at the University of Illinois Hospital and Health Sciences System between 1996 and 2011. Patients were identified by ICD-9 code for UEDVT. Variables collected include thrombotic risk factors and outcomes, including recurrent thrombosis and bleeding.

RESULTS

We identified 229 patients with UEDVT; 71% were African American, and 11% were diagnosed with sickle cell disease. The average number of UEDVT risk factors was 4.40 ± 1.5, the most common being central venous catheter (CVC) use (178, 78%). In the year following UEDVT, 13% experienced recurrent thrombosis, and 6% experienced major bleeding. Of 181 patients receiving warfarin after an UEDVT, 36% of international normalized ratio (INR) values were therapeutic. Patients with sickle cell disease had a lower proportion of INRs within the target range (25% vs 38%, P < 0.01), and were more likely to be lost to follow-up (67% vs 46%, P = 0.05) and experience a recurrent thrombotic event (29% vs 11%, P = 0.02).

CONCLUSION

A CVC is the most common risk factor for UEDVT; however, patients with sickle cell disease demonstrate additional unique demographics and risk factors. Patients included in this underrepresented demographic cohort had a low quality of anticoagulation control, particularly those with sickle cell disease.

Assessment of Dosing and Patient Factors on the Efficacy of Warfarin Following Total Joint Replacement

The purpose of this study was to determine the percentage of patients discharged with a subtherapeutic INR <1.8 using our institutions inpatient warfarin dosing nomogram following total joint arthroplasty (TJA). We examined predisposing risk factors for a subtherapeutic discharge (INR <1.8), including increased body weight, age, gender, end stage renal disease (ESRD), smoking, and peri-operative transfusion.

Chart review identified 249 patients for study inclusion. Logistic regression (LR) was used to identify associated risk factors for a subtherapeutic INR (<1.8) on day of discharge.

The majority of patients (58.6%, 146 of 249) following TJA surgery were found to have a subtherapeutic INR level (INR<1.8) at discharge (mean length of stay 2.6 days). Multivariate LR analysis found that weight greater than 180 lbs. (OR 2.08, CI 1.09, 3.98, P=0.027) was found to increase the odds of a subtherapeutic INR on day of discharge. Our results were not significant for weight 20% beyond ideal body weight, age (>65y), gender, peri-operative transfusion, smoking, ESRD or autoimmune disease.

A patient’s body weight influences response to warfarin following TJA. An inpatient warfarin dosing nomogram that takes into account a patient’s weight should be used to reduce the risk of subtherapeutic INR levels in obese TJA patients.

Thromboembolic and bleeding outcomes of extended duration low-intensity warfarin following elective total knee arthroplasty

INTRODUCTION

The purpose of this study was to describe the incidence of symptomatic venous thromboembolism (VTE), clinically-relevant bleeding, and death among a real-world population receiving warfarin prophylaxis targeting an international normalized ratio (INR) of 1.5 to 2.5 for four weeks following total knee arthroplasty (TKA).

MATERIALS AND METHODS

This retrospective, observational study included patients receiving warfarin following a TKA between August 1, 2005 and July 31, 2009 identified in the Kaiser Permanente Total Joint Replacement Registry. Patients<18 years, receiving warfarin for another indication, or without continuous KPCO membership during the study period were excluded.

RESULTS

There were 1487 patients with TKA included in the analysis. Mean patient age was 67.7 years and 61.7% were female. The median percent of time in therapeutic INR range during follow-up was 55% (interquartile range=35%-75%). Nineteen cases of symptomatic VTE [1.3%; 95% confidence interval (CI) 0.8%-2.0%] including ten pulmonary emboli (PE) (0.7%) were identified within 90 days of surgery. Clinically-relevant bleeding occurred in 1.7% (95% CI 1.1%-2.5%) of patients during warfarin prophylaxis and there were no deaths within 90 days of surgery.

CONCLUSIONS

The rates of symptomatic VTE and clinically-relevant bleeding following TKA in patients receiving warfarin prophylaxis with a target INR of 1.5 to 2.5 were low. Additional studies should include low-intensity warfarin to identify the regimen that optimally balances risks of bleeding and symptomatic VTE after major orthopedic surgery.