The use of warfarin therapy has declined over the last decade with the introduction of direct oral anticoagulants (DOACs). However, it remains the mainstay of treatment for several groups of patients including those with mechanical heart valves, valvular atrial fibrillation and antiphospholipid syndrome.
Safe and effective warfarin management requires regular international normalised ratio (INR) monitoring. The INR is a standardised test of blood coagulation that can be performed by venous blood test, usually processed by a hospital laboratory, or capillary blood test, performed using a point-of-care (POC) testing device, similar to devices used for monitoring blood sugar levels in diabetic patients. All patients taking warfarin have a therapeutic INR target range indicating the safest level of anticoagulation for them; typically, this is an INR value between 2 and 3. The aim of warfarin management is to balance over-anticoagulation and its associated risk of bleeding with under-anticoagulation and its associated risk of thrombotic events.
The COVID-19 pandemic disrupted the normal process of warfarin management since many warfarin patients were identified as ‘clinically extremely vulnerable’ and asked by the UK government to ‘shield’ (ie stay at home and avoid contact with others). Despite allowing for medical appointment attendance in the guidance, many patients were disinclined to do so for fear of contracting COVID-19.
Anticoagulation clinics were faced with the challenge of maintaining safe anticoagulation in patients reticent to come for INR tests. The need to prevent adverse events from over or under-anticoagulation had to be balanced with the risks of coronavirus transmission, particularly in light of the evidence suggesting an increased risk of supratherapeutic INRs in those who developed COVID-19 (Speed et al, 2020).
National guidance was first issued for maintaining safe anticoagulation by NHS England and NHS Improvement in 2020—since updated (NHS England and NHS Improvement, 2021)—with additional guidance following from the Medicines and Healthcare Products Regulatory Agency (2020).
National guidance (NHS England and NHS Improvement, 2021) supported a multi-faceted response; patients were reviewed for their potential to switch to a DOAC, which require less monitoring than warfarin (Patel et al, 2021), and those unable to switch to a DOAC were assessed for their ability to use POC testing for INR monitoring in their own homes. South East London Clinical Commissioning Group (SELCCG) responded by issuing its anticoagulation service providers with Roche CoaguChek XS INR POC testing devices for distribution to their most vulnerable patients. CoaguChek XS devices have been thoroughly tested and deemed a safe and effective device for INR monitoring by the National Institute for Health and Care Excellence (NICE) (2017).
King's College Hospital NHS Foundation Trust has anticoagulation clinics at two of its sites, one a large inner city teaching hospital, and the other a district general hospital based in an outer London suburb.
Before the pandemic, the clinics managed 128/4100 (3%) INR self-testing patients across the two sites. Although a relatively small proportion of the total number of patients, the clinics had experience supporting patients with self-testing and the necessary processes in place to ensure governance and safety using this method of testing. The protocol used by the Trust is based on the Pan London INR self-testing framework (London Stroke Clinical Network, 2016).
Overarching national guidance in place before the pandemic states that, where possible, patients on long-term warfarin and other vitamin K antagonists (VKAs) should be supported to self-test to reduce the number of hospital appointments required and also due to a potential reduction in the risk of bleeding and stroke (NICE, 2018).
This review aims to document the experience of a hospital-based anticoagulation service in southeast London in supporting patients to switch to INR self-testing. In particular, the review aims to describe the process of identifying patients suitable for switching to self-testing, describe the procedure for the training and issue of the devices, and evaluate the success of the intervention in terms of patient satisfaction and impact on warfarin control.
Method
Patient identification
The anticoagulation clinics at King's College Hospital NHS Foundation Trust care for a combined total of approximately 4100 warfarin (or alternative VKA) patients, therefore careful selection of patients who would benefit the most from self-testing, but also had the physical and cognitive capacity needed to perform self-tests, was necessary. The process involved identifying patients requiring long-term warfarin therapy with a clinical or social requisite for self-testing. Clinical factors considered by the teams included poor warfarin control, poor venous access, and needle phobia, while social considerations included being housebound, shielding during the COVID-19 pandemic, or being in full-time education or work (Table 1).
Table 1. Patient self-testing selection considerations
| Clinical/social need | Suitability |
|---|---|
|
|
Initiation of self-testing for INR monitoring
A shortlist of patients was compiled using warfarin dosing software and the clinical team's knowledge of the patients under their care. Selected patients were telephoned and further screened for their motivation as well as motor and cognitive ability to perform tests. If consenting and deemed to be able to self-test, they were invited to attend the hospital for a self-testing initiation appointment. The appointments were typically 45 minutes long and undertaken by anticoagulation clinical nurse specialists. They involved training the patient and/or carer how to use the device and performing an INR test on the patient's device and a correlation test on the clinic's POC device or venous laboratory test as a quality control. In line with local and national guidance (Jennings et al, 2014; London Stroke Clinical Network, 2016), patients were asked to review the Trust's INR self-testing policy and sign the document if they were in agreement with the conditions. The contract sets out the processes for patient self-testing and the roles and responsibilities of both the clinic and the patient to optimise quality of care and ensure patient safety (Figure 1).
Self-testing INR continuation
After the initial training appointment, patients were permitted to perform subsequent INR tests on their device at home and communicate results to the clinic by email or telephone. They were subsequently contacted by the clinic with their warfarin dose and next test date and asked to continue testing in this way, providing both parties were satisfied that the method was working for them. A small number of patients encountered difficulties using the device at home and required further support from the clinic, either via telephone or with an additional clinic appointment.
NICE (2018) guidance requires that equipment for self-testing is regularly checked for quality control by testing patients' equipment against a Trust device. At initiation of self-testing, patients were informed that they would be required to attend the hospital every 6 months to have their machine checked and perform a test on their own and the clinic's device to ensure good correlation. A variation of ≤0.5 between the two readings is deemed acceptable (London Stroke Clinical Network, 2016). Patients were given verbal and written guidance regarding the appropriate action according to their INR result as summarised in Table 2.
Table 2. Protocol for patient action according to international normalised ratio (INR)
| INR result | Action |
|---|---|
| Between 2 and 4.9 | Contact anticoagulation clinic for dosing advice as normal |
| Less than 2 | Repeat INR with POC on the same dayFor repeat INR use a different, clean finger and a new lancet and testing stripContact the clinic with both readings for advice |
| 5 and over | |
| Unrecordable | |
| Over 8 | Contact anticoagulation clinic and repeat INR with venous sample |
Anticoagulation control
A common way to assess anticoagulation control on warfarin is to review the percentage of time the patient spends with an INR within their therapeutic INR range, usually calculated over a 6- or 12-month period. This measure is termed ‘time in therapeutic range’(TTR) (Rosendaal et al, 1993).
Time in therapeutic range was measured for all patients for the 6-month period prior to self-testing and compared with the 6-month period after commencement of self-testing (where this was not possible, a minimum of 3 months after initiation of self-testing was used).
Patient experience of switching to self-testing
All patients were asked to complete a survey to assess their experience of the switching process. The survey was administered via telephone by a ward-based haematology nurse for all consenting patients 3-6 months after switching to self-testing. A staff member outside of the anticoagulation team was selected to perform the survey to encourage authentic responses but it is likely that some inherent bias remained. The survey consisted of 10 multiple-choice questions with the option to elaborate further. The survey explored the effectiveness of the training and support provided by the anticoagulation clinics, the viability of using self-testing machines for warfarin patients, the impact self-testing had on patient lifestyle and whether self-testing altered patient perception of their warfarin control.
Findings
Between June 2020 and January 2021, 71 patients and two nursing homes were trained in the use of the CoaguChek XS device at King's College Hospital NHS Foundation Trust. Only one patient was unable to use the device after training. The mean age was 54 years (range: 16-82 years) and 59% (42/71) were female. The predominant indication for anticoagulation in this cohort was venous thromboembolism (VTE) followed by ‘other’, which included indications such as left-ventricular thrombus, antiphospholipid syndrome and arterial thrombus and then mechanical heart valves (Figure 2).
Of the 71 patients initiated on self-testing, five ceased self-testing within 6 months, of these, one patient died and four patients did not master self-testing despite ongoing training and support, reinforcing the notion that patient selection is a very important determinant of success.
Anticoagulation control after switching to a POC device
The team found that, although modest, a statistically significant improvement in TTR was evident (mean before POC 52.0%, SD 24.8, vs mean after 60.7%, SD 19.7; P<0.009). It should be noted that causation of this improvement cannot be attributed to self-testing alone due to the many confounding factors, not least the effects of the global COVID-19 pandemic.
The number of missed INR test appointments (DNAs) in the new self-testing cohort of patients reduced by 39% in the 6-month period after self-testing was commenced compared with the 6 months prior.
Patient experience of switching to a POC device
In total 46/71 (65%) patients completed the satisfaction survey. The majority of respondents (39/46, 85%) stated that they found using the POC device ‘very easy’ or ‘easy’ during their training appointment, but this dropped to 67% (31/46) when performing the tests on their own at home. The main difficulty patients had both in training and at home was obtaining a sufficient sized blood sample for the test to work. Just over half the patients (24/46, 52%) managed to get an INR reading on the first attempt when at home, it took two or three attempts for 35% (16/46) of patients and 13% (6/46) needed four or more attempts. For safety purposes, patients were asked not to perform additional tests beyond those requested by the clinic, despite this, 46% (21/46) admitted to performing one to three additional tests and 2% (1/46) performed four or more additional tests. These additional test results were not always reported to the anticoagulation clinic.
High levels of satisfaction were found in self-testers, with 94% (43/46) stating that they were either ‘very satisfied’ or ‘satisfied’ with self-testing. Similarly, 85% (39/46) of patients in the survey said that self-testing had a ‘very positive’ or ‘positive’ impact on their lifestyle. In addition to the multiple choice answers, some patients expanded on the impact self-testing had on them:
‘I feel more in control; it has given me more confidence. I feel safe and looked after even without leaving my house.’
Many patients cared for by the central London hospital site rely on public transport to attend appointments—an additional risk and burden during the pandemic:
‘It made my life easier. I don't need to worry about going to the hospital. I'm not taking public transport anymore and I don't worry about COVID.’
One patient described a dissonant effect on them, referring to the difficulty they experienced in performing the tests:
‘I find it very convenient but more stressful.’
A minority of respondents (4%, 2/46) reported dissatisfaction and a negative impact on lifestyle. This outcome was seen in patients who had great difficulty performing INR tests independently at home, which led to feelings of frustration and anger. One of the few patients who reported a negative impact on their lifestyle described their lack of confidence in the device:
‘The machine gives me incorrect readings. That is my problem, I feel safer in hospital. Always incorrect reading and I returned it to the clinic.’
Patients were asked if they felt self-testing had influenced their warfarin control; 59% (27/46) felt there was no difference but 37% (17/46) perceived their control to be ‘much better’ or ‘somewhat better’. When their perceptions were compared with the actual difference in their warfarin control, 59% (26/43) were correct in their perception.
Discussion
Overall the switch to POC testing in this cohort was successful with high levels of patient satisfaction and significant improvements in warfarin control. For further roll out to be considered, cost-effectiveness must also be evaluated. A meta-analysis of 26 randomised controlled trials investigating the clinical and cost-effectiveness of POC testing for patients on warfarin therapy reported a modest but significant improvement in TTR associated with INR self-testing, concordant with the findings from this project. The meta-analysis also found evidence of a reduction in thromboembolic events and all-cause mortality (Sharma et al, 2015). The authors concluded that, without these improved health outcomes, self-testing was unlikely to be cost-effective when the cost of the machine, consumables, training and support were considered.
Conversely, NICE (2017) looked at the thromboembolic outcomes of 21 trials and found that, although warfarin self-management (self-testing and self-dosing) halved the risk of thromboembolic events compared with the standard care, there was no significant reduction in thromboembolic events associated with self-testing alone.
The other end of the risk spectrum for patients on warfarin is bleeding. The relationship between bleeding and INR self-testing remains uncertain. The meta-analysis by Sharma et al (2015) did not show a reduction in the number of minor or major bleeds in self-testing patients, whereas NICE (2017) found that minor bleeding rates actually increased in self-testing patients compared with those receiving standard of care (Sharma et al, 2015). This perhaps highlights the limitations of TTR as a safety and efficacy indicator since it does not take into consideration the distribution of INRs outside the TTR and is affected by the frequency of testing (Reiffel, 2017). A hypothesis requiring further investigation is that the reduced likelihood of self-testing patients missing tests, as seen in our population, may contribute to improved clinical outcomes.
Some strong themes emerged from the qualitative data gained from the survey, those of control, safety, independence and convenience. Patients appreciated the liberation from attending hospital appointments with all the associated challenges such as parking, travel costs, long waiting times and, during the pandemic, risk of contracting COVID-19. Patients also valued having control and autonomy over their warfarin management.
At present, the positive impact on lifestyle and patient satisfaction may provide the strongest rationale for promoting self-testing, given the disparities in the two reviews around clinical outcomes associated with self-testing (Sharma et al, 2015; NICE, 2017).
Conclusion
The use of INR self-testing in physically and cognitively able patients is advantageous, particularly in the context of a global pandemic. Benefits included high levels of patient satisfaction and a positive impact on patient lifestyle, as well as a reduction in missed appointments. Due to the associated costs of the equipment and clinical support, self-testing may not be cost-effective for all patients. Further data are needed to evaluate the incidence of safety and efficacy outcomes for warfarin patients self-testing with POC devices in comparison with venous blood draw testing.
KEY POINTS
- Point-of-care testing of International normalised ratio (INR) is a good option for motivated patients with sufficient cognitive and motor function
- Self-testing had a positive influence on warfarin control and test adherence in the chosen cohort
- Point-of-care testing was associated with excellent patient satisfaction and lifestyle impact outcomes
- Anticoagulation clinics need appropriate governance and safety protocols in place and the expertise to support patients to self-test
- Point-of-care testing is not cost efficient in all patients on warfarin therapy.
CPD reflective questions
- What are the challenges of managing patients taking warfarin therapy—particularly during a pandemic?
- What are the potential benefits of warfarin self-testing for patients and healthcare organisations?
- What governance and safety processes need to be in place for self-testing to be supported?