Increased hemostatic molecular markers in patients undergoing anticoagulant therapy

We evaluated several molecular markers of hemostasis in 92 patients with hypercoagulable states treated with anticoagulant therapy. In all patients, the average values of the international normalized ratio (INR) were 1.70 +/- 0.50; this increase in INR was not, however, significant in patients under thrombotest (TT) monitoring. There were no thrombotic or severe bleeding complications in these patients during a period of 27 months. Plasma levels of thrombin-antithrombin complex (TAT), plasmin-plasmin inhibitor complex (PPIC), D-dimer, and soluble fibrin monomer (sFM) were slightly increased, suggesting that anticoagulant therapy was not completely effective in our Japanese patients based on the values of the TT. The INR was negatively correlated with TT, protein C, and protein S and particularly with TT between 10 and 80%. The range of TT was not correlated with the plasma level of TAT, PPIC, D-dimer, or sFM, but the range of INR was correlated with the plasma level of TAT, D-dimer, and sFM. The percentage of TAT, D-dimer, and sFM within normal range was significantly lower in patients with high INR. These findings show that INR is better than TT for the monitoring of warfarin therapy and that the therapeutic values of INR during the anticoagulant therapy should be > 1.7 in Japanese patients.     

Diagnosis of disseminated intravascular coagulation by hemostatic molecular markers

In the present study, the positive rate of thrombin-antithrombin complex (TAT), plasmin-plasmin inhibitor complex (PPIC), soluble fibrin monomer (sFM), and D-dimer for the diagnosis of disseminated intravascular coagulation (DIC) was evaluated. The study comprised 307 patients with DIC, 123 with pre-DIC, and 121 with non-DIC. Plasma levels of TAT, PPIC, sFM, and D-dimer were significantly higher in DIC and pre-DIC patients than in non-DIC patients. In DIC patients, the positive rate of sFM was high and that of D-dimer was low; the positive rate of PPIC was higher in patients with hematopoietic malignancy than in those without this disease. In pre-DIC patients, the positive rate of all markers was low (<0.16), and the positive rate of PPIC was relatively high. In non-DIC patients, the positive rate of all hemostatic markers was low (<0.16), that of sFM being the lowest. Scoring the positive rate of TAT, PPIC, and sFM disclosed the following results: 72% of DIC patients had three or more points, 17.6% of pre-DIC patients had three or more points, and almost all (96.6%) non-DIC patients had two or less points. Scoring the positive rate of TAT, PPIC, and D-dimer disclosed the following results: 52.9% of DIC patients and 27.4% of pre-DIC patients had three or more points and almost all (96.7%) non-DIC patients had 2 or less points. These data suggest that the combination of TAT, PPIC, and sFM is useful for making the diagnosis of DIC.     

Hemostatic molecular markers before the onset of disseminated intravascular coagulation

We retrospectively measured various hemostatic markers in 240 patients with disseminated intravascular coagulation (DIC) before the onset of DIC and in 110 non-DIC patients, and examined their usefulness for the diagnosis of pre-DIC. Changes in prothrombin time ratio and fibrinogen levels were not significant before the onset of DIC. The plasma levels of fibrinogen and fibrin degradation products before the onset of DIC were increased and the platelet count was gradually reduced in nonleukemic patients; these changes were already significant in the non-DIC state. The plasma levels of thrombin-antithrombin complex (TAT), plasmin-plasmin inhibitor complex (PPIC), D-dimer, and soluble fibrin monomer (sFM) were increased before the onset of DIC. In leukemic patients, the plasma levels of sFM on day 5, those of TAT on day 3, and D-dimer on day 1, were significantly increased before the onset of DIC. The levels of most hemostatic markers 7 days before the onset of DIC were not different from those observed in the non-DIC state. In nonleukemic patients, only D-dimer, sFM, and TAT levels were significantly increased 7 days before the onset of DIC compared with values in the non-DIC state. The positive rate of hemostatic markers for the diagnosis of DIC, TAT, and PPIC were high during the pre-DIC and non-DIC groups. The plasma levels of sFM and D-dimer were low in non-DIC and increased gradually during the pre-DIC state. These findings suggest that hemostatic molecular markers such as sFM, D-dimer, and TAT are useful for the diagnosis of pre-DIC, although their cutoff values were different among various diseases.     

ISI/INR system in Japan: experience from simultaneous measurement of the same plasma at four different laboratories

In 1984, the Scientific and Standardization Committee (formerly ICTH) recommended the use of the International Sensitivity Index and International Normalized Ratio (ISI/INR) System for the monitoring of oral anticoagulant therapy. This system was introduced because the sensitivity of thromboplastin reagents used for the measurement of prothrombin time (PT) was widely different and comparison among hospitals employing different reagents was virtually impossible. In this study, we simultaneously measured the plasma from 7 patients with warfarin therapy at 4 different institutions for PT seconds, PT-INR, thrombotest (TT) seconds and TT-INR. The comparison between these laboratories revealed clinically important variances between the 4 laboratories even when PT was converted to PT-INR. Laboratory 1 and laboratory 3 were using the same thromboplastin reagents for the measurement of PT. The PT (seconds) in both laboratories showed similar numbers, but when they converted into INR, the variances were significant (maximum coefficient of variance 10.44). We investigated the reason why these differences occurred and found that the PT seconds (11.40) for normal control at laboratory 3 were somewhat larger than those of other laboratories. If we assume that PT-INR is identical to TT-INR, the estimated PT (second) for normal control at laboratory 3 can be calculated from TT-INR, and was found to be 10.56 +/- 0.10 seconds. This was nearly the same as the one that was used at laboratory 1. In conclusion, there still exist some difficulties that must be overcome before the ISI/INR system can be used reliably, and we suggest attention be given to the PT seconds used as normal control plasma.     

Optimal therapeutic range for oral anticoagulants in Japanese patients with prosthetic heart valves: a preliminary report from a single institution using conversion from thrombotest to PT-INR

The thrombotest (TT) technique has been widely used in Japan for monitoring oral anticoagulant therapy (OAT). The therapeutic range was originally recommended to be 10%–25%. However, the International Committee for Standardization in Hematology/International Committee on Thrombosis and Hemostasis (ICSH/ICTH) recommended using the international normalized ratio of prothrombin time (PT-INR) for monitoring OAT. It is necessary to use a universal standard measure for monitoring OAT in accordance with the ICSH/ISTH recommendation. We simultaneously measured TT and PT in blood samples from 1 157 patients on long-term warfarin therapy, and studied the correlation between TT and PT-INR. An excellent linear correlation was obtained between TT-INR and PT-INR with the regression equation PT-INR = 1.0420 TT-INR − 0.0987 (r = 0.905, P < 0.001). We also examined the correlation between the incidence of thromboembolism in 170 patients receiving warfarin therapy after prosthetic valve replacement; 50.5% received concomitant antiplatelet therapy. Thromboembolism occurred in 9 of 170 patients during a mean follow-up period of 2.44 years. The average TT values in patients with and without thromboembolism were 26.4% (PT-INR: 1.53) and 21.1% (1.73), respectively (P < 0.01). The incidence of thromboembolism did not differ significantly between patients on warfarin alone (average TT: 22.2%) and those on warfarin and antiplatelet agent (average TT: 20.9%). Our results suggest that the incidence of thromboembolism is low in Japan despite a less intensive regimen having been adopted. Received: June 22, 2000 / Accepted: October 4, 2000     

Decreased tissue factor and tissue-plasminogen activator antigen in relapsed acute promyelocytic leukemia

This study evaluated hemostatic data in 28 patients with newly diagnosed acute promyelocytic leukemia (APL) and 15 patients with relapsed APL. Activated partial thromboplastin time and prothrombin time were prolonged at initial onset of APL. Plasma level of fibrinogen was significantly decreased in patients with initial disease of APL, but it was not decreased significantly during the relapse of APL. Plasma fibrin and fibrinogen degradation products levels were significantly increased and platelet counts significantly decreased in both groups. Plasma levels of antiplasmin significantly decreased at initial onset but not during relapse. Plasma levels of antithrombin were within normal range in patients with initial disease but significantly decreased in those with relapse. Plasma levels of D-dimer, soluble fibrin monomer (sFM), plasmin-plasmin inhibitor complex (PPIC), and thrombin antithrombin complex (TAT) levels were significantly high in both groups. Plasma levels of PPIC, sFM, and D-dimer were significantly higher at initial onset of APL than during relapse. However, there was no significant difference in DIC score between patients with initial onset and those with relapse; plasma levels of tissue factor (TF) significantly increased in both groups, but they were significantly higher at initial onset of APL than during relapse. TF and tissue type plasminogen activator (t-PA) antigen levels in leukemic cell lysate were significantly increased in both groups, and they were significantly lower during relapse than at initial onset. Hemostatic abnormalities occurring in patients with relapsed APL might be the result of the decrease of TF and t-PA in leukemic cells. These findings suggest that DIC in APL patients with relapse might not be caused only by TF and t-PA and thus should be treated with different therapy from patients with initial onset of APL.     

高龄心房颤动患者抗血小板与抗凝策略的临床观察

目的 观察高龄心房颤动(房颤)患者抗血小板治疗与抗凝治疗现状及有效性和安全性. 方法 根据高龄房颤患者住院时的治疗情况分为华法林抗凝组(15例)和阿司匹林(或氯吡格雷)抗血小板组(52例)进行分析.每组分别测定用药前后的凝血酶原时间(PT)、活化凝血时间(ACT)、国际标准化比值(INR)、部分活化凝血活酶时间(APTT)、纤维蛋白原(FIB)、凝血酶时间(TT)、凝血因子(Ⅱ、Ⅴ、Ⅶ、Ⅷ、Ⅸ、Ⅹ)活性、纤维蛋白降解产物(FDP)和D-二聚体. 结果抗血小板组平均治疗时间(44.2±37.5)个月.抗凝组平均治疗时间(39.0±61.5)个月.抗血小板组有6例发生缺血性脑卒中,1例发生急性右下肢动脉栓塞,3例发生消化道出血.抗血小板组用药前后PT、ACT、INR、APTT、FIB、TT、凝血因子(Ⅱ、Ⅴ、Ⅶ、Ⅷ、Ⅸ、Ⅹ)活性比较、差异均无统计学意义.抗凝组共发生2例消化道出血及2例致死性出血性脑卒中.抗凝组华法林用药后PT延长(8.4±7.5)s,ACT下降(0.49±0.22)s.INR升高0.93±0.83,凝血因子Ⅱ、Ⅶ、Ⅸ及Ⅹ活性均较用药前有显著降低(均P<0.05). 结论 抗凝治疗能够有效预防高龄房颤患者的缺血性脑卒中发生,但出血事件发生率可能增多,总体不良事件发生并未显著减少.     

Evaluation of the phospholipid-rich dilute Russell's viper venom assay to monitor oral anticoagulation in patients with lupus anticoagulant.

The International Normalized Ratio (INR) is generally recommended to monitor anticoagulant therapy in patients treated with warfarin. However, there has been concern about the validity of the INR to monitor warfarin therapy in patients with lupus anticoagulant, particularly when there is prolongation of the baseline INR. An alternative approach is to use a chromogenic factor X assay that is not sensitive to lupus anticoagulant. However, this assay is expensive, not widely available, and does not have an established therapeutic range. We hypothesized that the phospholipid-rich dilute Russell viper venom time (prdRVVT), a simple, rapid and inexpensive assay, might be suitable to monitor warfarin therapy in this situation since Russell's viper venom directly activates coagulation factor X while the phospholipid in the reagent reduces or negates any effect of lupus anticoagulant on the assay. We measured the INR, chromogenic factor X, and prdRVVT in 50 patients stabilized on warfarin for at least 6 weeks, 12 of whom had lupus anticoagulant, and 37 patients not taking warfarin, 17 of whom had lupus anticoagulant. Factor X was negatively correlated with INR in anticoagulated patients both in the absence (r = -0.45, P = 0.01) and presence (r = -0.43, P = 0.17) of lupus anticoagulant. The prdRVVT was also strongly correlated with INR in anticoagulated patients without lupus anticoagulant (r = 0.60, P < 0.0001) but there was no correlation in the presence of lupus anticoagulant (r = -0.13, P = 0.68). Our results suggest that the prdRVVT is not suitable for monitoring warfarin therapy in patients with lupus anticoagulant.     

Monitoring Therapy with Vitamin K Antagonists in Patients with Lupus Anticoagulant: Effect on Different Tests for INR Determination

Background: Lupus anticoagulant (antiphospholipid antibodies) is associated with venous and arterial thrombosis in patients with and without autoimmune disorders. Vitamin K antagonists are the treatment of choice in patients with thrombosis, of which the dose is titrated by INR monitoring. Several recent reports suggest that the presence of the lupus anticoagulant disturbs the INR test and may lead to unreliable results with a large variation in INR values, dependent on the reagents used.Methods: We studied 11 lupus anticoagulant positive patients and 11 lupus anticoagulant negative patients, all using vitamin K antagonists. The INR value was determined using seven different tests and the variation in INR values was compared between the two groups. The amidolytic Factor X levels were used as an phospholipid independent measure for intensity of warfarin therapy. Factor VII and X activity were measured to assess the stability of warfarin therapy.Results: The variation of the results with different INR tests within one patient was minimal and comparable in the two groups for INR's in the therapeutic range. The coefficient of variation for the cases and control group was 10.43 and 9.35, respectively. Variation in both groups increased at supratherapeutic levels of anticoagulation and when the anticoagulation was unstable (measured with Factor X/Factor VII ratio). The relationship between INR values and Factor X analysis revealed no influence of the lupus anticoagulant.Conclusions: In this study, lupus anticoagulant antibodies do not disturb INR laboratory tests. Differences in INR measurements are seen in patients with a high intensity of anticoagulation and in patients who either just started or in whom no stable anticoagulation has been achieved.Abbreviated Abstract. This study investigates the influence of lupus anticoagulant on INR determination tests in patients treated with warfarin. Eleven cases and eleven lupus anticoagulant negative control patients, also on warfarin therapy, were included. Seven INR results per patient were obtained using different laboratory tests. A factor X assay was performed to obtain an independent measure for the intensity of warfarin therapy.The variation of INR results between the cases and controls revealed no difference in these groups. In addition, the relationship between INR values and Factor X analysis indicated no influence of the lupus anticoagulant. What was observed was an increased difference in INR values in patients with a high intensity of anticoagulation and in patients who either just started or in whom no stable anticoagulation has been achieved     

中国汉族人群CYP3A4基因变异对华法林初始抗凝治疗反应性的影响

目的探讨细胞色素P450酶3A4基因(cytochrome P-450 3A4,CYP3A4)多态性对中国汉族人华法林初始抗凝治疗反应性的影响。方法入选2000年至2008年在广东省人民医院行瓣膜置换术后长期口服华法林抗凝治疗的中国汉族患者798例。通过文献检索,选取与华法林药动学可能相关的CYP3A4的2个SNPs多态性位点(rs2242480、rs2246709),采用SNaPshot进行基因单核苷酸多态性(SNP)的检测,并按基因型分组,分别比较CYP3A4不同基因型间华法林日平均剂量、凝血酶原时间国际标准化比值(prothrombin time-internationalnormalized ratio,PT-INR)达标时间和过度抗凝发生率的差异。群体代表性检验采用Hardy-Weinberg遗传平衡检验。结果在华法林初始治疗的20 d内,华法林日剂量在男性明显高于女性,差异有统计学意义[(2.92±1.18)mg/dvs.(2.64±0.98)mg/d,P0.05],而PT-INR达到目标值(1.8)平均需要时间和初始治疗阶段过度抗凝的比率在男女之间比较,差异无统计学意义(P0.05)。CYP3A4不同基因型之间华法林日剂量、达标时间和过度抗凝比率比较,差异均无统计学意义(P0.05)。结论 CYP3A4基因变异对中国汉族人群初始治疗20 d内的华法林日剂量无明显影响,常规剂量给药方案在服药初期CYP3A4突变个体出血风险无明显增加。     

心房颤动患者抗凝治疗前后微栓子及血浆D-二聚体水平观察

目的：观察心房颤动患者华法林治疗前后微栓子检出率及血浆 D-二聚体水平。方法选择 CHADS2评分≥1分的持续性房颤患者40例,每例患者华法林抗凝治疗前后分别行微栓子监测和 D-二聚体水平检查,比较治疗前后结果差异。结果抗凝治疗前微栓子阳性12例、阴性28例,治疗后微栓子阳性5例、阴性35例,抗凝治疗后微栓子检出率显著降低（30．0％ vs．12．5％,χ2＝3．66,P ＜0．05）;D-二聚体水平抗凝治疗前为（273±81）μg／L,治疗后为（170±67）μg／L。治疗后血浆 D-二聚体水平显著降低（t ＝10．09,P ＜0．05）。结论微栓子与 D-二聚体水平均可以作为房颤患者栓塞风险的评估指标。     

华法林对超高龄患者抗凝治疗价值研究

目的分析华法林抗凝治疗在80岁以上患者中临床应用的现状,评价其临床适应证、疗效及风险,探讨在超高龄患者中华法林的合理应用方法。方法回顾性分析2006年1月至2010年12月于北京大学第一医院心内科31例华法林抗凝治疗的80岁以上患者的临床资料,总结华法林的起始及维持剂量、国际标准比值(INR)监测及栓塞和出血事件的发生。结果 93.55%患者均属于被动抗栓治疗。70.97%的患者INR达2.0～3.0,70.97%的患者达标剂量<3 mg/d,41.94%的患者维持1.5 mg起始剂量。发生缺血性卒中2例,INR<2.0;出血事件2例,INR>2.5。结论 80岁以上超高龄患者的华法林抗凝治疗,1.5 mg/d的起始剂量安全有效;INR维持在2.0～2.5较为适宜。     

Comparative evaluation of warfarin utilisation in two primary healthcare clinics in the Cape Town area

Background

Although warfarin remains the anticoagulant drug of choice in a wide range of patients, its narrow therapeutic window makes patients susceptible to a high risk of bleeding complications or failure to prevent clotting. This has necessitated therapeutic monitoring in warfarinised patients. Factors that could be responsible for the fluctuating responses to warfarin vary from pharmacogenetic to concomitant morbidity, diet and medication. In order to assess the quality of management of warfarin treatment in a local primary-care setting, the current study evaluated warfarin utilisation and monitoring records in two hospitals with different patient groups.

Methods

A retrospective study was undertaken in the specialised warfarin clinics at Wesfleur and Gugulethu hospitals (Western Cape, South Africa) covering all warfarin-related therapy records over a 12-month period. Data extracted from the patients’ folders included age, gender, race, weight, address, concurrent chronic illnesses, treatment and medication, indication for warfarin and INR history.

Results

A total of 119 patients’ folders were analysed. Attendance at the clinics reflects the demographics and racial distribution of the host location of the hospitals. While all the patients were maintained above the minimum international normalised ratio (INR) value of 2, about 50% had at least one record of INR above the cut-off value of 3.5. However, over a third of the patients (32.2%) had at least one record of INR greater than 3.5 in Gugulethu Hospital, compared to over half (58.3%) in Wesfleur Hospital.In total, atrial fibrillation was the most common indication for warfarinisation while hypertension was the most common concurrent chronic condition in warfarinised patients. All patients who received quinolone antibiotics had INR values above the cut-off point of 3.5 within the same month of the initiation of antibiotic therapy, suggesting drug-induced warfarin potentiation. Other co-medications, including beta-lactam antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs) and anti-ulcer drugs appeare to alter warfarin responses as measured by recorded INR values.

Conclusion

The study found inter-individual variability in the response to warfarin therapy, which cut across racial classifications. It also confirms the possible influence of concomitant morbidity on patient response to anticoagulant therapy.     

Standardization of Prothrombin Time/International Normalized Ratio (PT/INR)

The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized ratio (INR) for use in monitoring anticoagulant therapy with vitamin K antagonists such as warfarin in order to provide test results that are adjusted for thromboplastin and instrument used. The INR is created using two major PT ‘correction factors’, namely the mean normal PT (MNPT) and the international sensitivity index (ISI). Manufacturers of reagents and coagulometers have made some efforts to harmonizing INRs, for example, by tailoring reagents to specific coagulometers and provide associated ISI values. Thus, two types of ISIs may be generated, with one being a ‘general’ or ‘generic’ ISI and others being reagent/coagulometer-specific ISI values. Although these play a crucial role in improving INR results between laboratories, these laboratories reported INR values are known to still differ, even when laboratories use the same thromboplastin reagent and coagulometer. Moreover, ISI values for a specific thromboplastin can vary among different models of coagulometers from a manufacturer using the same method for clot identification. All these factors can be sources of error for INR reporting, which in turn can significantly affect patient management. In this narrative review, we provide some guidance to appropriate ISI verification/validation, which may help decrease the variability in cross laboratory reporting of INRs.     

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.     

Relationship between prothrombin time international normalized ratio and thrombo test (%)]

OBJECTIVES: The optimal therapeutic range for laboratory evaluation of oral anticoagulant therapy is now defined by the prothrombin time international normalized ratio (PT-INR). However, the thrombo test (TT), an alternative method to measure intensity of anticoagulation, is also currently used throughout Japan. The relationship between PT-INR and TT (%) has yet to be clarified. This study investigated the relationship between PT-INR and TT (%). METHODS: The PT-INR and TT (%) were simultaneously measured of 505 consecutive samples from patients treated with warfarin in our hospital. Fourteen functions were used for regression analyses: a fractional function (Y = a/X + b), a square root function (Y = aX0.5 + b), a natural logarithmic function (Y = a.lnX + b), a power series function (Y = aXb), a quotient function (Y = abX), and polynomial functions [Y = anXn + an - 1Xn - 1 +......+ a1X1 + b, (1 < or = n < or = 9)]. The results were confirmed by the same methods in 383 samples and 296 samples from another two laboratories. RESULTS: The power series function showed the most significant (p < 0.0001) and highest adjusted R2 (0.858) correlation, with a regression formula of TT (%) = e4.48 (PT-INR)-2.09 in our laboratory. Using the same analyses, the power series function also showed the most significant and highest adjusted R2 in samples from the other two laboratories. CONCLUSIONS: This study showed that a power series function is the most appropriate for expressing the relationship between PT-INR and TT (%) among the 14 functions. The function between PT-INR and TT (%) is mainly derived from the relationship between TT (%) and TT (sec). Both internal validity and external validity confirmed the relationship between PT-INR and TT (%).     

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.     

Home prothrombin time monitoring: a literature analysis

The anticoagulant activity of warfarin sodium is monitored by the prothrombin time (PT) using the international normalized ratio (INR). Standard oral anticoagulant therapy monitoring requires frequent patient visits to physicians' offices and/or laboratories to optimize warfarin dosage. Home PT monitoring by patients can increase testing frequency and may thus decrease complications associated with oral anticoagulant therapy. Clinical studies suggest that home PT monitoring is more effective than uncoordinated management and is as effective as care through specialized anticoagulation clinics for keeping INRs within a therapeutic range. There are accurate and reliable instruments available, but paramount to the success of home PT monitoring is sound patient selection, appropriate patient training, and consistent quality control.     

Evaluation of the blood coagulation mechanism and platelet aggregation in individuals with mechanical or biological heart prostheses.

Oral anticoagulants have been widely employed to decrease thrombotic risk by reducing the levels of vitamin K-dependent clotting factors. Paradoxically, the use of oral anticoagulants also decreases the levels of natural anticoagulants (protein C and protein S), which favors the hypercoagulability state. Increased platelet activation has been reported in patients undergoing warfarin treatment. These findings have raised questions about the antagonistic effect of oral anticoagulants and their implications for hemostatic balance. The aim of this study is to determine the relationship between warfarin dosage and prothrombin time [International Normalized Ratio (INR)], platelet aggregation, vitamin K-dependent clotting factors, and protein C and protein S. Blood samples from 27 patients were analyzed, seven with mechanical prostheses and 20 with biological prostheses, and 27 controls. Multiple regression analysis showed that factor II most significantly determines the INR. Results showed that the INR, clotting factors, and protein C and protein S activity did not correlate with warfarin dosage, highlighting the need for accurate laboratory monitoring of those undergoing anticoagulant therapy.     

Determination of markers of coagulation activation and reactive fibrinolysis in patients with mechanical heart valve prosthesis at different intensities of oral anticoagulation.

In a group of 60 patients with mechanical heart valve prosthesis prothrombin fragment 1 + 2, thrombin-antithrombin III complexes and D-dimer have been determined in order to assess the residual coagulation activation and the extent of the reactive fibrinolysis. The patients were divided into three subgroups of 20 patients each with different intensities of oral anticoagulation as indicated by International Normalized Ratio (INR) values in the ranges 4.8-3.6, 3.5-2.5 and 2.4-2.1. From the two markers of coagulation activation studied (prothrombin fragment 1 + 2 and thrombin-antithrombin III (TAT)) the prothrombin fragment 1 + 2 was dependent on the INR level in all groups, although the median values were still significantly beneath the lower limit of the reference range. The D-dimer concentrations were unexpectedly high with respect to the low coagulation activation levels, as indicated by the D-dimer/TAT and D-dimer/F 1 + 2 ratios. This demonstrates the enhanced presence of fibrin degradation products as a scarcely described side-effect of oral anticoagulation. The anticoagulant properties of fibrin degradation products might contribute partly to the in vivo haemorrhagic risk in high-intensity oral anticoagulation. These results show, inasmuch as the prothrombin fragment 1 + 2 is concerned, that from the laboratory point of view the residual thrombin activity is low enough to be adequate under the therapeutical regimen followed in this study. However, the question of the efficacy of anticoagulation intensities can only be finally answered by clinical trials.