Point-of-care devices for measuring coagulation status in people receiving long-term vitamin K antagonist therapy allow both self-testing and self-management, defined as follows:
l Self-testing: point-of-care test carried out by the patient with test results managed by their health-care
provider [e.g. general practitioner (GP), nurse, specialised clinic].
l Self-management: point-of-care test carried out by trained patient, followed by interpretation of test
result and adjustment of dosage of anticoagulant according to a predefined protocol.
Self-testing and self-management are together referred to as self-monitoring for the purposes of this report. The purpose of this assessment was to appraise the current evidence for the clinical effectiveness and
cost-effectiveness of self-monitoring (self-testing and self-management) using either the CoaguChek®
system (Roche Diagnostics, Basel, Switzerland), the INRatio2®PT/INR monitor, (Alere Inc., San Diego, CA,
USA) or the ProTime Microcoagulation system®(International Technidyne Corporation, Nexus Dx, Edison,
NJ, USA), compared with standard clinical monitoring in people with atrial fibrillation or heart valve disease for whom long-term vitamin K antagonist therapy is indicated.
All of these point-of-care devices, which are currently available for use in the NHS, are CE marked and Food and Drug Administration (FDA) approved. Point-of-care instruments work basically in the same way: a drop of capillary whole blood is obtained by a finger puncture device, applied to a test strip and inserted into a coagulometer. However, they differ in terms of methods of clot detection and general
intended for patient self-monitoring. The CoaguChek XS model comprises a meter and specifically designed test strips for blood sample analysis (fresh capillary or untreated whole venous blood). The CoaguChek XS system purports to have the following advantages over the CoaguChek S: (1) the thromboplastin used in the prothrombin time test strips is a human recombinant thromboplastin, which is more sensitive and has a lower International Sensitivity Index (ISI) of 1.0 compared with 1.6; (2) test strips have onboard quality control that is automatically run with every test, rather than having to perform external quality control; (3) test strips do not have to be refrigerated; (4) a smaller blood sample can be used; and (5) the meter is smaller and lighter. The CoaguChek XS Plus model is aimed primarily at health-care professionals and possesses additional features to the XS system, including increased storage and connectivity for data management.
Summary of INRatio2 PT/INR monitor
The INRatio2 PT/INR monitor performs a modified version of the one-stage prothrombin time test using a recombinant human thromboplastin reagent. The clot formed in the reaction is detected by the change in the electrical impedance of the sample during the coagulation process. The system consists of a monitor and disposable test strips and the results for prothrombin time and INR are reported.
Summary of ProTime Microcoagulation system
The ProTime Microcoagulation system is designed for measuring prothrombin time and INR. The test is performed in a cuvette which contains the reagents. Two different cuvettes are available depending on the amount of blood that needs to be collected and tested: the standard ProTime cuvette and the ProTime3 cuvette.
Identification of important subgroups
There are a number of clinical conditions which require long-term vitamin K antagonist therapy to reduce the risk of thrombosis. These conditions include atrial fibrillation and heart valve disease.
Atrial fibrillation
Atrial fibrillation results in unorganised atrial electrical activity associated with mechanically ineffective fibrillation, that contraction which can lead to blood stagnating in parts of the atria and as a result forming a clot. This clot may then move from the heart, causing thromboembolism, most commonly in the brain where it causes stroke. People with atrial fibrillation are at a five to six times greater risk of stroke, with 12,500 strokes directly attributable to atrial fibrillation every year in the UK. Treatment with warfarin reduces the risk by 50–70%.1,22,23
Artificial heart valves
Valve disease can affect blood flow through the heart in two ways: valve stenosis, where the valve does not open fully, and valve regurgitation (or incompetence), where the valve does not close properly, allowing blood to leak backwards. The most effective treatment for many forms of valve disease is heart valve replacement. Replacement heart valves are either artificial (mechanical), or from humans or animals (tissue). The human valve could be from the same patient (autograft) when the native pulmonary valve is used in the aortic position (part of the Ross procedure); or from another patient (heterograft). People with mechanical heart valves generally require long-term anticoagulant treatment to prevent clotting related to the valve.
l the patient (or a designated carer) is both physically and cognitively able to perform the self-monitoring test
l an adequate supportive educational programme is in place to train participants and/or carers
l the patient’s ability to self-manage is regularly reviewed
l the equipment for self-monitoring is regularly checked via a quality control programme.
Comparators
In UK clinical practice, INR monitoring is currently managed by a range of health-care professionals, including nurses, pharmacists and GPs. INR monitoring can be carried out in primary care and secondary care. Primary care anticoagulant clinics use point-of-care tests or laboratory analysers. In the latter, blood
samples are sent to a central laboratory based at a hospital (‘shared provision’). In the case of secondary
care, INR monitoring can be carried out in hospital-based anticoagulant clinics using point-of-care tests or laboratory analysers.