Self-monitoring of warfarin is safe and cost-effective

This NIHR-funded systematic review investigated the clinical and cost-effectiveness of self-monitoring by people receiving long-term anticoagulation using vitamin K antagonists, most commonly, warfarin. People receiving warfarin require regular blood tests to see how their blood is clotting and to adjust their dose to avoid bleeding from too high a dose or thrombosis (clots) if the dose drops too low. This is usually done at their GP practice or in hospital clinics. Self-monitoring involves two aspects of care; people self-testing their blood on a machine at home and self-managing, adjusting their warfarin dosage themselves.

This review found self-monitoring halved the number of blood clots compared with standard care. Health and social costs were more equal, but the two devices had an 80% chance of being value for money at the usual threshold for the NHS. Self-monitoring could be offered to people who would like to self-monitor, and where they, or their carer, are able to do so.

Why was this study needed?

Oral anticoagulants are used to treat a variety of heart and blood vessel conditions that raise the risk of blood clots and stroke.  These drugs “thin the blood” helping to lower the risk of blood clots. But they also raise the risk of bleeding. Around 1.4% of UK adults require long-term oral anticoagulant therapy. Warfarin is the most commonly prescribed.

People taking warfarin require regular blood tests to monitor whether they are striking a safe balance between preventing blood clots and raising the risk of bleeding. These might be needed every week, or up to every eight weeks, and usually involve a trip to the GP practice or hospital clinic.

Self-monitoring allows people to monitor themselves (self-test) and adjust their warfarin dose (self-management) at home. This is potentially more convenient for the person, and benefits the NHS by reducing costs associated with GP or hospital visits.

The NIHR-funded this systematic review for NICE to help with producing guidance on the use of self-monitoring.

What did this study do?

This systematic review of randomised controlled trials that evaluated the clinical and cost effectiveness of self-monitoring using three blood monitoring systems: CoaguChek®, INRatio2® PT/INR monitor and ProTime Microagulation system®. The review included trials comparing these self-monitoring systems with standard care, monitoring by GP or hospital clinics, in people needing long-term anticoagulation because of atrial fibrillation (irregular and often fast heartbeat) or heart valve disease.

The systematic review was well designed. However, the authors note that the definition of standard care varied greatly between studies. This means different studies may not have been comparing like with like. 22 of the 26 trials included were judged to be at medium or high risk of bias, so this bias within the studies may affect the reliability of the results.

What did it find?

  • 26 trials were included in the clinical effectiveness review; the majority (22 trials) evaluated the CoaguChek® system.
  • Self-monitoring led to almost a halving of blood clots compared with standard care (relative risk [RR] 0.58, 95% confidence interval [CI] 0.40 to 0.84). There were 54 thromboses among 2403 people self-monitoring, compared to 106 of 2237 on standard care.  There was no significant difference in the number of bleeds (major and minor) between self-monitoring and standard care.
  • Looking specifically at people with artificial heart valves: testing combined with adjustment of anticoagulant dose halved the risk of blood clots (RR 0.56, 95% CI 0.38 to 0.82) and death from any cause (RR 0.54, 95% CI 0.32 to 0.92) compared with standard care. There was no significant difference for people who were self-testing only, without adjusting the dose.
  • There was little difference in the total health and social care costs at 10 years between self-monitoring (£7,333 CoaguChek®, £7,295 InRatio2®, £8,609 ProTime) and standard care (£7,324). They estimated the number of blood clots would be 2.4% lower at 10 years using self-monitoring compared with standard care. Improved clinical outcomes would off-set initial and on-going costs of self-monitoring, such as training costs and annual device cost. Driven by the reduced number of clots, self-monitoring with CoaguChek XS® or INRatio2® had about an 80% chance of being cost-effective at the usual threshold ratio of £20,000 per QALY gained.
  • The proportion of blood test results staying within the recommended range was comparable for self-monitoring (52 to 80%) and standard care (55 to 77%). Adherence was generally high for self-monitoring (around 90% across 13 trials) and preference for self-monitoring was high (77 to 98% in four trials). Few people reported difficulties in using the self-monitoring devices.

What does current guidance say on this issue?

2014 NICE guidance recommends the use of the CoaguChek® or INRatio2® PT/INR by people with atrial fibrillation or heart valve disease, who would prefer to self-monitor, and if they or their carer are physically and cognitively capable of self-monitoring. These recommendations are based on the findings of this systematic review, combined with the expertise of the Diagnostics Advisory Committee.

What are the implications?

The findings of this systematic review informed 2014 NICE guidance, recommending that self-monitoring be offered option to people with atrial fibrillation or heart valve disease who would like to self-monitor and where either they – or their carer – are able to do so.

Non-vitamin K anticoagulants are available. They require less monitoring and dose adjustment but are not suitable for everyone, so vitamin K antagonists are still needed. This systematic review found that self-monitoring was clinically effective at reducing blood clots and was cost-effective compared with standard care, monitoring by either a GP or hospital clinic.


Sharma P, Scotland G, Cruickshank M et al. The clinical effectiveness and cost-effectiveness of point-of-care tests (CoaguChek system, INRatio2 PT/INR monitor and ProTime Microcoagulation system) for the self-monitoring of the coagulation status of people receiving long-term vitamin K antagonist therapy, compared with standard UK practice: systematic review and economic evaluation. Health Technol Assess 2015; 19(48).

This project was funded by the National Institute for Health Research HTA programme (project number 13/06/01).


British Heart Foundation. Warfarin. London: British Heart Foundation; no update date given.

Heneghan C, Ward A, Perera R et al. Self-monitoring of oral anticoagulation: systematic review and meta-analysis of individual patient data. Lancet 2012;379(9813):322-34.

Heneghan CJ, Garcia‐Alamino JM, Spencer EA, et al. Self‐monitoring and self‐management of oral anticoagulation. Cochrane Database Syst Rev. 2016;(7):CD003839.

NHS Choices. Anticoagulants, warfarin. London: Department of Health; updated 2013.

NICE. Atrial fibrillation and heart valve disease: self‑monitoring coagulation status using point‑of‑care coagulometers (the CoaguChek XS system and the INRatio2 PT/INR monitor). DG14. London: National Institute for Health and Care Excellence; 2014.

Tompson A, Heneghan C, Fitzmaurice D et al. Supporting patients to self-monitor their oral anticoagulation therapy: recommendations based on a qualitative study of patients' experiences.  Br J Gen Pract 2014;65(636):e438-46.

Ward A, Tompson A, Fitzmaurice D et al. Cohort study of Anticoagulation Self-Monitoring (CASM): a prospective study of its effectiveness in the community. Br J Gen Pract 2015;65(636):e428-37.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


Expert commentary

The NIHR Health Technology assessment adds to a substantial evidence base that supports self-monitoring and self-management of oral anticoagulation.

This review is supplemented by a recent NIHR-funded study which reported that even with little training people on oral anticoagulation can successfully self-monitor, and even self-manage, in the community. Individual patient data analysis with 12,800 person-years of follow-up has reported that self-monitoring was effective in the long term and across a wide age range of participants.

Therefore the evidence clearly supports the adoption of self-monitoring as part of a co-ordinated anticoagulation pathway that better supports effective strategies to reduce thromboembolic events in high risk individuals.

Professor Carl Heneghan, Professor of Evidence-Based Medicine and Director of CEBM, Nuffield Dept of Primary Care Health Sciences University of Oxford

Author commentary

This systematic review highlights that self-monitoring of anticoagulation appears to be safe and cost-effective. Based on this, National Institute for Health and Care Excellence (NICE) issued a policy guidance recommending CoaguChek® system and INRatio2® PT/INR coagulometers for self-monitoring of anticoagulation therapy. Paucity of evidence for alternative technologies hampered the comparisons according to the type of coagulometers. This uncertainty may impact on decision making as to which device(s) should be adopted in clinical practice. Further research assessing the longer-term outcomes of self-monitoring as well as the comparative effectiveness of various point-of-care coagulometers would be useful.

Pawana Sharma, Research Fellow, Health Services Research Unit, University of Aberdeen