Blood viscosity and oral anticoagulant therapy.

During administration of bishydroxycoumarin, hematocrit, viscosity of whole blood, and viscosity of plasma decreased in samples from nine healthy volunteers and 31 patients who had coronary heart disease. The relationships between viscosity of blood and intensity of anticoagulant therapy varied from patient to patient. Discontinuation of the drug was followed by return of viscosities to pretreatment levels in two to four days. The decrease of viscosity of blood by anticoagulant therapy may explain the relief of anginal pain in patients who have coronary heart disease.     

Control of oral anticoagulant therapy

In an effort better to standardize the control of oral anticoagulant therapy, it has recently been recommended that the prothrombin time be reported in the form of an International Normalized Ratio (INR) based upon calibration of the locally employed thromboplastin with an International Reference Preparation. It has been demonstrated in our laboratory that the INR does minimize the differences in results which ensue from variations in the source of thromboplastin and instrumentation and should hopefully allow for better interlaboratory comparisons in the future. Recent studies have also suggested that many American patients tend to be over anticoagulated and at greater risk for hemorrhage. Based upon those findings, over 40 percent of our specimens were above the currently recommended levels.     

The efficacy of long-term oral anticoagulant therapy and its laboratory assessment.

The activated partial thromboplastin time is compared with the corresponding prothrombin ratio in 6378 samples of platelet-poor plasma from 446 patients treated for a total of more than 4500 patient/months with oral anticoagulatnts. A relative decrease in the activated partial thromboplastin time following deep vein thrombosis is described, which tends to become less obvious during the first year of treatment and is greater in older patients. Although this relative decrease is also found in patients treated after cerebrovascular accidents, it is not found in patients treated after myocardial infarction or in patients with mitral valve disease treated prophylactically with long-term oral anticoagulants. It is though possible that these changes following deep vein thrombosis might be useful in helping to determine the duration of oral anticoagulant treatment.     

Maintenance control of oral anticoagulant therapy by a chromogenic substrate assay for factor X.

An amidolytic assay employing the chromogenic substrate S 2337 (Kabi Diagnostica) was used to assay factor X in 35 healthy controls and in 100 outpatients receiving oral anticoagulant therapy. This method correlated well with a coagulation assay of factor X in the control group (r = 0.88). When compared with two routine tests for the control of anticoagulant theray (Thrombotest and prothrombin ratio) good correlation was obtained between the methods, r = 0.84 and r = -0.74 respectively. These results suggest that a chromogenic substrate assay for factor X might be a suitable method for the maintenance control of oral anticoagulant therapy.     

Survey of oral anticoagulant treatment in children.

AIMS: To find out which children are treated with oral anticoagulants and how their treatment is controlled in the United Kingdom. METHODS: Two questionnaires were used. The first was sent to general haematologists and the other to paediatric cardiologists and cardiac surgeons. RESULTS: There were 273 (58%) replies to the first questionnaire. Most children were treated because of artificial cardiac valve replacement. The mean target International Normalised Ratio (INR) used was 2.73 to 4.0 for children with heart valves and 2.1 to 3.25 for children with venous thrombosis. The second questionnaire elicited replies from 11 of 22 cardiac centres. The mean target INR used for children with cardiac valves ranged from 2.59-3.77. Of 68 children covered in the survey, there have been two major bleeds and two thrombotic episodes: 78.8% of children were controlled with a venous prothrombin time and 21.2% with a capillary test. There was no consistency in the dose regimens used for the induction of oral anticoagulant treatment with warfarin. CONCLUSIONS: The levels of anticoagulation used for maintenance are similar to those recommended by the British Society for Haematology for adults (3.0 to 4.5). They seem to be safe for children too.     

A critical evaluation of the prothrombin time for monitoring oral anticoagulant therapy

The Quick prothrombin time is the most common clotting test performed, principally for monitoring oral anticoagulant therapy. The International Normalized Ratio (INR) for comparing patient results from prothrombin time measurements and the International Standardized Index (ISI) for achieving greater consistency of results using different thromboplastins have made it possible to compare the results of vitamin K antagonist drug therapy that was impossible before the introduction of the INR and ISI. However, INR values obtained from the same patient plasma sample using different thromboplastins are significantly different. This is so even when the thromboplastins have nearly the same ISI values. We suggest that investigation of patient-specific differences can provide a means by which the INR discrepancies can be identified and understood and thus lead to better methods for monitoring oral anticoagulant therapy.     

A micromethod prothrombin time for oral anticoagulant control.

A capillary prothrombin time method was described using the Australasian Reference Thromboplastin (A.R.T.). The method was used for the control of oral anticoagulant therapy in 59 patients on 225 occasions and was found to be reliable and convenient. The capillary prothrombin ratio could be correlated with the conventional plasma prothrombin ratio.     

Control of oral anticoagulant treatment by chromogenic prothrombin assay.

Doses of oral anticoagulants in 50 patients on long term treatment were easily and satisfactorily monitored over six months by an automated chromogenic assay of prothrombin (CPA). It is suggested that chromogenic assay of one or more of the vitamin K dependent coagulation factors would provide a readily standardised alternative to those conventional tests which depend on human brain derived reagents, now regarded as a biohazard.     

Computer assisted anticoagulant therapy

The constantly workload increase has led to the development of Computerised Decision Support Systems (CDSS) for a better management of patient care. Many clinical situations have been investigated to verify the utility of CDSS: few have demonstrated stable effects. One area where success has been reported is the field of oral anticoagulation management. CDSS system has demonstrated to be able to improve the treatment quality in comparison to manual method. In the future scenario of oral anticoagulant management CDSS will have a pivotal part, the constant increase of patients number and their pressure on thrombosis centres had led to the development of alternative models for delivery OAT: Primary care, General Practitioner, Patient self testing and self management and the use of CDSS has been central to the decentralisation process and may be useful in maintaining the efficacy and quality of anticoagulant control. GP with the aid of CDSS are able to deliver OAT as well as expert physician of Thrombosis Centre in terms of time spent by patient in therapeutic range.