Warfarin anticoagulation and outcomes in patients with atrial fibrillation: a systematic review and metaanalysis

OBJECTIVE: To examine the relationship between international normalized ratio (INR) and outcomes (major bleeding events and strokes) in patients with atrial fibrillation (AF) receiving anticoagulation with warfarin. METHODS: A systematic review and metaanalysis of studies published in the English language between January 1, 1985, and October 30, 2002, was performed. MEDLINE (PubMed), Current Contents, and relevant reference lists were searched. Studies enrolling patients with nonvalvular AF receiving warfarin anticoagulation were eligible for inclusion if they reported stroke and/or major bleeding events in relation to INR, or time spent in therapeutic range. The risk of bleeds in overanticoagulated patients (INR > 3) and the risk of strokes in underanticoagulated patients (INR < 2) were assessed. RESULTS: Twenty-one studies (6,248 patients) met all inclusion criteria. Of the 21 studies, a target conventional INR of 2 to 3 was used in 9 studies. An INR < 2, compared with an INR > or = 2, was associated with an odds ratio (OR) for ischemic events of 5.07 (95% confidence interval [CI], 2.92 to 8.80). An INR > 3, compared with an INR < or = 3, was associated with an OR for bleeding events of 3.21 (95% CI, 1.24 to 8.28). On average, in the four studies with a target INR range of 2 to 3, patients with AF receiving warfarin spent 61% of time within, 13% of time above, and 26% below the therapeutic range. CONCLUSION: Available evidence indicates that in patients with nonvalvular AF, the risk of ischemic stroke with insufficient warfarin anticoagulation (INR < 2), and the risk of bleeding events with overanticoagulation (INR > 3) are significantly higher relative to patients with AF maintained within the recommended INR of 2 to 3. However, the published data are sparse, heterogeneous, and primarily reported from clinical trials. More studies evaluating clinical outcomes in relation to INR are needed, especially in a real-world setting.     

Management and dosing of warfarin therapy

When initiating warfarin therapy, clinicians should avoid loading doses that can raise the International Normalized Ratio (INR) excessively; instead, warfarin should be initiated with a 5-mg dose (or 2 to 4 mg in the very elderly). With a 5-mg initial dose, the INR will not rise appreciably in the first 24 hours, except in rare patients who will ultimately require a very small daily dose (0.5 to 2.0 mg). Adjusting a steady-state warfarin dose depends on the measured INR values and clinical factors: the dose does not need to be adjusted for a single INR that is slightly out of range, and most changes should alter the total weekly dose by 5% to 20%. The INR should be monitored frequently (eg, 2 to 4 times per week) immediately after initiation of warfarin; subsequently, the interval between INR tests can be lengthened gradually (up to a maximum of 4 to 6 weeks) in patients with stable INR values. Patients who have an elevated INR will need more frequent testing and may also require vitamin K1. For example, a nonbleeding patient with an INR of 9 can be given low-dose vitamin K1 (eg, 2.5 mg phytonadione, by mouth). Patients who have an excessive INR with clinically important bleeding require clotting factors (eg, fresh-frozen plasma) as well as vitamin K1.     

Direct international normalized ratio determination using multicalibrators is more responsive than the conventional method for measuring prothrombin time

Direct international normalized ratio (INR) determination using certified INR plasmas was shown to improve precision and accuracy. We evaluated the utility of a multicalibrator in determining INR. INR values were measured in 493 blood samples from patients subjected to anticoagulation therapy (320) and control subjects (173). Study was performed using CA-7000 coagulation analyzer (Sysmex, Japan) with Thromborel S (Dade Behring, Germany). Direct INR values were obtained using PT-Multi Calibrator (Dade Behring) composed of five lyophilized calibrant plasmas. Conventional INR values were calculated from mean normal prothrombin time and instrument/reagent-specific international sensitivity index (ISI). We compared the difference between the INR results obtained with the two methods. The mean INR value of direct INR method was significantly higher than that of conventional method. The differences in values (direct INR – conventional INR) generated using the two methods increased in proportion to the INR values. Elevation of INR was observed in data obtained with the direct INR method, compared with conventional INR values. Accordingly, we conclude that direct INR method is more responsive than conventional method in determining INR.     

Preoperative INR and postoperative major bleeding and mortality: A retrospective cohort study

Little research has been done on the current cut-off international normalized ratio (INR) value of 1.5 for patients undergoing surgery. The objectives of this study are to assess the association between INR and postoperative major bleeding and mortality in patients undergoing surgery and to identify an ideal pre-operative INR for surgical patients. We analyzed data from the American College of Surgeons’ National Surgical Quality Improvement Program database between 2008 and 2011 (636,231 patients). The primary outcomes were major bleeding and mortality at 30 days postoperatively. Multivariate logistic regression analyses were carried out to assess these associations. Compared to an INR of <1, the adjusted odds ratio (aOR) for major bleeding was 1.22 (95 % CI 1.18–1.25) for INR 1–1.49, 1.48 (95 % CI 1.40–1.56) for INR 1.5–1.9, and 1.49 (95 % CI 1.39–1.60) for INR ≥2. The aOR for mortality at 30 days post-operation compared to INR of <1 was 1.51 (95 % CI 1.41–1.62), 2.31 (95 % CI 2.12–2.52), and 2.81 (95 % CI 2.56–3.10) for INR 1–1.49, 1.5–1.9, and ≥2, respectively. The ideal pre-operative INR value to predict an increased risk for major bleeding was 1.10 and 1.13 for mortality. In conclusion, preoperative INR is significantly and independently associated with postoperative major bleeding and mortality.     

CoaguChek XS血凝仪检测国际标准化比值和凝血酶原时间的准确性和可靠性

目的比较罗氏CoaguChek XS快速凝血分析仪与标准实验室静脉血测定的国际标准化比值(INR)和凝血酶原时间之间的差异,判断CoaguChek XS测量INR的准确性。方法 80例患者同时抽取静脉血及指端毛细血管血,分别行标准实验室INR测定及罗氏CoaguChek XS快速凝血分析仪INR测定。结果 2种测量方法差异无统计学意义(P0.05)。CoaguChek XS INR与标准实验室测定的INR呈正相关(r=0.987,P0.05)。92.5%的患者更愿意接受CoaguChek XS测定INR。结论罗氏CoaguChek XS快速凝血分析仪测定INR结果可靠,具有快速、简便、准确、疼痛小、依从性好等特点,能很快提供可靠数据,便于临床医师及时调整抗凝药物剂量。     

International normalized ratio control and subsequent clinical outcomes in patients with atrial fibrillation using warfarin

Journal of Thrombosis and Thrombolysis - We explored associations between INR measures and clinical outcomes in patients with AF using warfarin, and whether INR history predicted future INR...     

Anti-Xa and anti-IIa drugs alter international normalized ratio measurements: potential problems in the monitoring of oral anticoagulants.

Several of the newly developed anti-Xa and anti-IIa agents have been shown to influence the International Normalized Ratio (INR) values. During phase I trials with normal healthy volunteers and phase II study patients who were given warfarin and concomitant anti-IIa or anti-Xa agents, it has been reported that INR values were falsely elevated. It is of critical importance to know of the effects of these agents on INR to avoid dosage errors. To study the influence of these agents on INR, we used several anti-IIa agents (argatroban, recombinant hirudin, efegatran, and PEG-hirudin) and anti-Xa drugs (pentasaccharides such as fondaparinux and idraparinux, DX-9065a and JTV-803). The anti-IIa drugs were supplemented in citrated plasma at a concentration of 0 to 1 microg/mL level and anti-Xa drugs in the range of 0 to 25 microg/mL. The IC(50) values for each of these agents were calculated. Four different commercially available prothrombin time (PT) reagents were used to perform the PT assays and to calculate the relative INR values. Direct synthetic factor IIa and Xa inhibitors exhibited a concentration-dependent increase in the INR values. Hirudin, efegatran, and PEG-hirudin showed a weaker effect, whereas argatroban showed a much higher elevation of the INR values. Synthetic indirect anti-Xa agents such as the pentasaccharide did not show any effect on the INR values. Furthermore, prothrombin time reagents with high ISI values exhibited disproportionally higher INR values for both the direct anti-Xa and anti-IIa agents. Elevation of INR values has therapeutic implications when non-oral anticoagulant drugs are used in combination with drugs such as warfarin. Because of the false elevation of INR values with some of the non-oral anticoagulant drugs, patients who are on concomitant warfarin therapy should be carefully evaluated for their corresponding INR values for proper dosing. To avoid dosing errors it is best not to use the INR values in the therapeutic monitoring of anti-Xa and anti-IIa agents either in the monotherapeutic or polytherapeutic modalities. These data also warrant the development clinically relevant methods for the monitoring of the concomitant use of newly developed anti-Xa and anti-IIa drugs with oral anticoagulants.     

European Concerted Action on Anticoagulation. Correction of displayed international normalized ratio on two point-of-care test whole-blood prothrombin time monitors (CoaguChek Mini and TAS PT-NC) by independent international sensitivity index calibration

The international normalized ratio (INR) on two widely used point-of-care test (POCT) prothrombin time (PT) monitors (CoaguChek Mini and TAS PT-NC) differed considerably and also differed from the 'true' INR obtained on the same samples using a manual PT and the same species thromboplastin international reference preparation. Agreement between the displayed INR and difference from 'true' INR has been reassessed following an independent international sensitivity index (ISI) calibration of the two systems. The displayed INRs taken at seven centres were compared with 'true' INRs from the same blood donations and INRs based on the resulting ISI. The overall difference between the displayed INRs on the two monitor systems was reduced from 21.0% to 3.5%. The overall difference in mean INR of system A from the 'true' INR was reduced from 19.0% to 9.5% and of system B from 6.8% to 0.3%, but individual centre's results still showed considerable mean INR variability. Differences between overall displayed INR with the two monitor systems have been reduced by an independent multicentre calibration, and agreement with 'true' INR on the same blood samples improved. However, marked variability in mean INR at individual centres remained after ISI correction, which demonstrates the need for external quality control of individual POCT whole-blood PT monitors.     

Patient self-testing is a reliable and acceptable alternative to laboratory INR monitoring

SAn ageing population and the continuing expansion of clinical indications for coumadin therapy have increased pressure on hospital anticoagulant clinics. One solution is patient self-testing (PST) of the international normalized ratio (INR) using capillary blood samples on point-of-care coagulation monitors at home. We conducted a prospective study to determine whether patients can achieve accurate INR values through PST, using the CoaguChek S (Roche Diagnostics, Lewes, UK). The main outcome measurements were: comparability of INR values obtained by PST and the hospital laboratory, patient acceptability as assessed by a questionnaire and anticoagulant control. Eighty-four patients [53 men, 31 women; median age 59 years (range 26-83)], receiving long-term oral anticoagulation (warfarin), were recruited from our Anticoagulation Clinic. Patients were randomized to weekly self-testing or continuing 4-weekly hospital laboratory monitoring of INR. Comparison of INRs (n = 234) showed no significant differences between the CoaguChek (median INR 3.02) and laboratory testing (median INR 3.07). There was excellent correlation between the two methods (r = 0.95), with 85% of CoaguChek results within 0.5 INR units of the laboratory method. On four occasions, differences of >1 unit INR were obtained, but in each case the patient's anticoagulation was unstable (INR >4.5 by both methods) and the differences in INR would not have altered patient management. 87% of patients found self-testing straightforward, 87% were confident in the result they obtained and 77% preferred self-testing. We conclude that PST is a reliable alternative to hospital clinic attendance and is acceptable to the majority of suitably trained patients.     

Mathematical derivative applied to international normalised ratio and analytical variations in oral anticoagulant therapy control

A reliable prothrombin time (PT) testing and a careful drug dosage can prevent thrombotic or bleeding complications of the oral anticoagulant therapy. The international normalised ratio (INR) as PT standardisation introduced an analytical variation that increases with higher PT measures and higher international sensitivity index (ISI) values. Our study was conducted to investigate the INR accuracy through the mathematical derivative application to reduce the analytical component of the INR uncertainty. The evaluation of accuracy among four different systems (prothrombin activity percent, PT seconds, PT ratio and INR) was determined by the simulation of a systematic error. Plasma samples were diluted 1:2; then they were compared observed with the expected values. We analysed the calculation system of the INR through the mathematical derivative in 87 PT ratio measurements. The analytical incidence of thromboplastin ISI was performed through an elaboration of INR mathematical derivative considering 10 different ISI values ranging from 1.1 to 2. The data expressed as PT ratios revealed a lower systematic error propagation suggesting that a linear system is more accurate. According to the calculation formula of INR, analytical variability increases with the PT measurements, then with the intensity of anticoagulation. Mathematical derivative suggests that the INR uncertainty due to the ISI can be reduced using a thromboplastin reagent with a low ISI or with ISI close to 1.     

An international collaborative study on the INR calibration of freeze-dried reference plasmas

A study was carried out to calibrate potential European Reference Plasmas for prothrombin time (PT) standardization. The International Normalized Ratio (INR) values of three freeze-dried candidate plasmas (one pooled normal and two pools from anticoagulated patients) were determined in 20 laboratories using six thromboplastin reagents comprising three International Reference Thromboplastins (human, rabbit and bovine), two recombinant human reagents and one placental human reagent. Interlaboratory variability of INR estimation was low with geometric coefficients of variation (gcv) <10% except in one case. Significant differences in mean INR were found between the different thromboplastins with lowest INR values found with the bovine reagent. INR values from the International rabbit and human reagents differed by <6% and were combined to give proposed assigned INR values. Significant differences in INR estimates from four thromboplastins of human origin may indicate that single assigned INR values are not applicable for use with all thromboplastin reagents. Field trials to assess the validity of single assigned INR values in clinical practice are required.     

Reliability of delayed INR determination: implications for decentralized anticoagulant care with off-site blood sampling

In order to develop decentralized anticoagulant care by off-site blood sampling and transport of samples to a centralized laboratory for International Normalized Ratio (INR) determination we have performed a direct comparative study of INR stability. Analysis was performed daily for 5 d using nine thromboplastins. The overall mean difference of INR after 3 d was only 0.05 INR units for samples with a therapeutic INR. After 5 d there was a mean difference of 0.11 INR units with 'non-Manchester' reagents and 0.44 INR units with 'Manchester' reagents. With over-anticoagulated samples mean differences of 0.55–0.72 INR units were observed after 3 d and 1.16–2.46 INR units after 5 d. Although there was some variation in stability of results with different thromboplastins, the difference over time with each thromboplastin was much less than the difference between thromboplastins.
In conclusion, there is no clinically significant change in INR when analysis is delayed for up to 3 d. Off-site blood sampling can accommodate a large increase in patient workload without a major revenue increase in primary care and with continued total quality management and central expert advice.     

Accuracy, reproducibility and clinical utility of the CoaguChek S portable international normalized ratio monitor in an outpatient anticoagulation clinic

The accuracy and reproducibility of the CoaguChek S, and its clinical agreement with conventional laboratory international normalized ratio (INR) determination, were evaluated in an outpatient anticoagulation clinic setting. Forty-three patients provided 248 paired INR measurements for analysis. The paired results were highly correlated (r = 0.90). The mean coefficient of variation for the CoaguChek S for a random sample of 21 patients with three repeated tests each, was 4%. Clinical applicability was also measured by discrepant INR values, as defined in the literature by expanded and narrow agreement, and by INR values resulting in a different clinical decision by a blinded haematology registrar. Expanded agreement and narrow agreement between the two INR values occurred 90 and 88% of the time, respectively. The stricter criteria set down by the clinician resulted in 73% of paired results producing the same dosage decision. The CoaguChek S displayed good correlation with laboratory determination of INR and compared relatively well with expanded and narrow clinical agreement criteria.     

Bleeding events and associated factors in a cohort of adult patients taking warfarin in Sarawak,Malaysia

Evidence is emerging that rates of adverse events in patients taking warfarin may vary with ethnicity. This study investigated the rates of bleeds and thromboembolic events, the international normalised ratio (INR) status and the relationship between INR and bleeding events in Malaysia. Patients attending INR clinic at the Heart Centre, Sarawak General Hospital were enrolled on an ad hoc basis from May 2010 and followed up for 1 year. At each routine visit, INR was recorded and screening for bleeding or thromboembolism occurred. Variables relating to INR control were used as predictors of bleeds in logistic regression models. 125 patients contributed to 140 person-years of follow-up. The rates of major bleed, thromboembolic event and minor bleed per 100 person-years of follow-up were 1.4, 0.75 and 34.3. The median time at target range calculated using the Rosendaal method was 61.6 % (IQR 44.6–74.1 %). Of the out-of-range readings, 30.0 % were below range and 15.4 % were above. INR variability, (standard deviation of individuals’ mean INR), was the best predictor of bleeding events, with an odds ratio of 3.21 (95 % CI 1.10–9.38). Low rates of both major bleeds and thromboembolic events were recorded, in addition to a substantial number of INR readings under the recommended target range. This may suggest that the recommended INR ranges may not represent the optimal warfarin intensity for this population and that a lower intensity of therapy, as observed in this cohort, could be beneficial in preventing adverse events.     

Impact of short-term hypothyroidism on systemic anticoagulation in patients with thyroid cancer and coumarin therapy.

Unlike hyperthyroidism, few data exist regarding the impact of hypothyroidism on systemic anticoagulation with coumarin derivates. Therefore, we evaluated a potential impact of short-term hypothyroid conditions on systemic anticoagulation with coumarin derivates in patients after complete thyroidectomy for treatment of thyroid cancer. Fifteen patients with differentiated thyroid cancers and continued international normalized ratio (INR)-adjusted therapy with coumarin derivates were included in this retrospective analysis. A total of 88 laboratory tests was analyzed. INR values were compared between thyroid-stimulating hormone (TSH) values greater than 10 and 10 mU/L or less. An INR value of less than 2.0 was defined as being out of the therapeutic range. Analysis of significant differences between categorized TSH and INR values were performed by using X(2) analysis, correlation of continuous TSH and INR values by using the Pearson's analysis. When TSH was greater than 10 mU/L (n = 50) the INR value was less than 2.0 in 76.0% (n = 38) cases. In contrast, the INR value was less than 2.0 in only 21.1% (n = 8; p < 0.0001) of patients with TSH of 10 mU/L or less (n = 38). Correlation between continuous TSH and INR values was r = -0.589 (p < 0.0001). Based on the results of the present study, it seems to be necessary to monitor the anticoagulation parameters more often in patients with hypothyroidism and either to correct the hypothyroid state, or in cases of desired hypothyroid conditions, to adjust the therapy with coumarin derivates in order to ensure a sufficient anticoagulation.     

Renal artery stenosis in hypertensive patients with antiphospholipid (Hughes) syndrome: outcome following anticoagulation

OBJECTIVE: We have demonstrated a point prevalence of 26% renal artery stenosis in patients with antiphospholipid syndrome (APS) and uncontrolled hypertension. We describe the effect of anticoagulation on blood pressure control and renal function. METHODS: We studied 23 patients retrospectively with renal artery stenosis (RAS). Fourteen received oral anticoagulation for more than 1 yr (target International Normalized Ratio (INR) of 3.0-4.5). Five patients had primary APS. Patients were divided into two groups based on their INR (< 3.0 and > or = 3.0). Nine patients had repeat magnetic resonance angiography (MRA) or an angiogram of the renal arteries after 2 yr. RESULTS: Only 8/14 patients managed to maintain their INR > or = 3.0 (median INR 3.1, range 2.8-3.7) while six had a INR < 3.0 (median INR 1.9, range 1.2-2.4). Patients with a median INR < 3.0 had poorly controlled blood pressure and there was significant deterioration in mean serum creatinine values (Wilcoxon's test, P < 0.03). Nine patients underwent follow-up renal artery imaging. Three of nine patients with an INR < 3.0 (median INR 1.9) had re-stenosis and a fourth developed bilateral renal artery stenosis. Five patients with INR > or = 3.0 (median INR 3.1) did not show re-stenosis of the renal arteries; their renal function was stable and blood pressure was well controlled. One other patient with secondary APS (mixed connective tissue disorder) with INR > 3.0 showed recanalization of the stenosed renal artery. CONCLUSION: Anticoagulation with INR maintained > or = 3.0 helped to control the blood pressure and prevent the progression of renal disease.     

老年心房颤动病人华法林抗凝治疗的有效性安全性评价

目的　评价华法林用于老年心房颤动病人抗凝治疗的有效性、安全性。方法　选择符合本研究抗凝标准的132例老年心房颤动病人随机分为两组 ,华法林治疗组 (治疗组 ) 5 8例 ,给予华法林 3mg/ d开始 ,监测凝血酶原时间(PT)及国际标准化比值 (INR) ,7～ 15 d使 INR达到 1.8～ 2 .5范围内 ,以后每月查 1次 INR。若病人增加或减少药物有出血倾向时随时再测 INR。阿司匹林对照组 (对照组 ) 74例 ,给予阿司匹林 30 0 mg/ d,分 2次口服 ,密切随访。结果　治疗组 7～ 15 d,平均 (9.1± 2 .8) d,INR达 1.8～ 3.0 (平均 2 .1± 0 .13) ,其中 INR在 1.8～ 2 .5 (平均 1.92±0 .2 3)之间者占 92 .7% ,治疗组有 1例心瓣膜病人出现脑梗死 ,而对照组有 7例发生脑梗死 ,差异显著 ,其余不良反应率两组差异无显著性。结论　老年心房颤动病人选择华法林 2～ 3mg/ d时 ,加强服药后监测及各药物间的相互作用 ,使 INR保持在 1.8～ 2 .5之间是有效、安全的     

Reversible and irreversible binding of fibrinogen to platelets

Abstract

Atrial fibrillation (AF) is the most common sustained arrhythmia and associated with adverse outcomes and increased risk for thromboembolic events. Warfarin is still the most extensively prescribed oral anticoagulant in AF to prevent ischemic complications. We aimed to determine the differences at platelet indices with warfarin usage layered by International Normalized Ratio (INR). A total of 250 patients with permanent non-valvular AF (mean age 70.2?±?9.1; 153 female) were divided into two groups. Group 1 included 125 patients whose INR is between 2.0 and 3.0 (called as “effective”) and Group 2 included 125 patients whose INR is <2.0 (called as “ineffective”). Also 123 age- and sex-matched individuals in sinus rhythm enrolled as control group (Group 3). After physical and echocardiographic examination, complete blood counts and INR were studied. There was no statistically significant difference in age, sex, co-morbidities and medications, also hemoglobin, white blood cell and platelet counts among the groups. The CHA₂DS₂-VASc scores were similar between Groups 1 and 2. The mean platelet volume (MPV), platelet distribution width (PDW) and plateletcrit (PCT) were significantly higher in Group 2 than Groups 1 and 3 and similar between Groups 1 and 3. MPV was positively correlated with PDW and PCT and also inversely correlated with INR value and platelet count. On multivariate logistic regression analysis, MPV, PDW and PCT were independent predictors of ineffectiveness of INR. The results of this study showed that MPV, PDW and PCT are increased in patients with non-valvular AF without effective warfarin treatment. Warfarin usage adjusted by INR is associated with lower values of these platelet indices, even lower as the values of subjects in sinus rhythm. MPV, PDW and PCT are independent predictors of INR ineffectiveness and seem to be useful parameters for monitoring the effectiveness of warfarin treatment.     

Effects of anticoagulation on infarct size and clinical outcome in acute cardioembolic stroke

Effects of anticoagulation on infarct size and outcome have not been fully elucidated in patients with acute cardioembolic stroke, although the anticoagulation therapy reduces both occurrence and recurrence of ischemic stroke greatly. The authors retrospectively investigated the relationship of anticoagulation intensity to infarct size and outcome. In 104 consecutive patients (mean age 70.8 +/- 10.0 years) who had suffered acute supratentorial cardioembolic infarction or transient ischemic attacks, they analyzed risk factors for atherosclerosis, underlying heart diseases, the infarct size (maximal area) on brain computed tomography, and modified Rankin scale score upon discharge. They compared these clinical data between patients who had received warfarin before the ictus and those who had not. In addition, they investigated the effects of the international normalized ratio (INR) on infarct size and outcome in 19 patients who had been receiving anticoagulant therapy and had measurement of INR within 24 hours after stroke onset. There were 25 patients who had received anticoagulation before the stroke (A/C group) and 79 patients who had not (non-A/C group). The infarct size in the A/C group tended to be smaller than that in the non-A/C group (p = 0.081, Mann-Whitney U test). In the 19 patients who had prior anticoagulation and measurement of INR within 24 hours of stroke onset, large infarcts were seen in 6 of 13 patients with INR < 1.6 and in none of 6 patients with INR > or = 1.6. Poor clinical outcome was observed in 5 patients with INR < 1.6, but in none with INR > or = 1.6. In conclusion, anticoagulant therapy with INR > or = 1.6 appears to effectively prevent a large infarct and poor outcome, even when ischemic stroke dose occurs in patients with an emboligenic heart disease.     

Assessment of agreement and time in therapeutic range of capillary versus venous international normalised ratio in frail elderly people in a nursing home

Vitamin K antagonists are widely used, yet have a slim therapeutic margin and high iatrogenicity. Patients are monitored through international normalised ratio (INR) by venipuncture, but coagulometers could measure INR by capillary puncture. This prospective study evaluated the clinical concordance of capillary INR versus venous INR in 31 nursing home patients. Concordance was good and mean time in therapeutic range (TTR) markedly increased. Capillary INR is thus reliable, could improve TTR and decrease iatrogenicity.