Inter-test Reliability of Point of Care Platelet Function Tests
Research type
Research Study
Full title
Inter-test Reliability of Point of Care Platelet Function Tests: An Aid to Risk Stratification Prior to Regional Anaesthesia in Patients Taking Clopidogrel - A pilot cross-sectional study
IRAS ID
244631
Contact name
Elliott Sharp
Contact email
Sponsor organisation
Brighton and Sussex University Hospitals NHS Trust
Duration of Study in the UK
0 years, 8 months, 21 days
Research summary
Research Summary
Many people with peripheral arterial disease take clopidogrel (a blood thinning drug). National guidelines recommend stopping clopidogrel 7 days before anaesthesia and surgery to prevent excess bleeding. For emergency surgery, stopping 7 days early is not possible.
New and quick blood tests exist called "platelet function tests" that measure numerically how thin someone’s blood is. These tests may be able predict someone’s risk of excess bleeding during anaesthesia and surgery which may reduce patient harm. How the results of different tests compare to each other is not clear as patients do not routinely have multiple tests performed on their blood.
Our main aim to able to compare the results of these two tests to improve how reliably these tests can predict excess bleeding in patients.
With the data we collect, we will also be able to estimate if people with peripheral arterial disease respond to clopidogrel as they are expected to.
We will achieve these aims by recruiting participants who will be attending a claudication clinic as part of their routine care at our hospital. They will initially be approached by their vascular nurse specialist and then meet with a researcher. If they provide informed consent, 6ml of blood (approximately one tablespoon) from each participant. After this, the patient will not have any more contact with the researchers.
This blood sample will be then be analysed by the researcher using two different platelet function tests. The results of these two tests will be compared and adjusted for variables contained within the participant's medical notes thought to affect platelet function and clopidogrel metabolism.
Summary of Results
Point of care platelet function tests to aid pre-operative decision making: A cross-sectional study comparing Multiplate® and TEG® 6S results in patients with peripheral arterial disease taking clopidogrel
Overview and purpose of the study
This was a single centre cross-sectional study (an observational study analysing data from a group of people at a single point in time), sponsored by University Hospitals Sussex NHS Foundation Trust. It was approved by the Health Research Authority and funded by the Vascular Anaesthesia Society of Great Britain and Ireland. The study was conducted by members of the Sussex Peri-operative Research Team at the Royal Sussex County Hospital (RSCH) in Brighton led by Dr Vanessa Fludder, consultant anaesthetist. A patient advisory group was consulted during the study design; they helped to ensure that the patient information leaflet was written in a way that was easy to understand. Participants (n = 58 in total) were recruited between October 2019 and September 2023 from the vascular ward (n = 23 patients) and out-patient clinics (n = 35).
This research was designed to help address the question: Do two commonly available point of care (POC - otherwise known as near-patient or bedside testing) platelet function tests (PFTs) give the same results as each other and how well are the test results correlated? It is important to know the answer to this question to help us develop the best guidance for clinicians using POC PFTs when deciding on timing of surgery and type of anaesthesia for urgent limb (or life) -saving surgery on blood vessels.
Background
Platelets are a component of blood involved in clotting. Platelet function tests measure platelet activity and how much the activity is affected by drugs such as clopidogrel. When clopidogrel works as expected, it delays blood clotting and helps to prevent complications of arterial disease. Published evidence suggests that clopidogrel doesn’t work as well as expected in a high proportion of people with peripheral arterial disease (PAD – a blockage of the blood vessels affecting blood supply to the legs).
PAD is a common problem, affecting approximately 1 in 5 people over the age of 60. Each year in the UK approximately 14,000 patients will have an operation to treat PAD and a large proportion of them are taking clopidogrel. This is because national guidance recommends people with PAD are treated with clopidogrel to prevent worsening of vascular disease.
Occasionally clopidogrel can work better than expected resulting in an increased risk of bleeding. It is important to detect any increased risk of bleeding before embarking on surgery. Currently, to minimise any risk of bleeding associated with clopidogrel, guidelines suggest that people stop taking it for 5-7 days before surgery. Sometimes this is not possible, such as in urgent or emergency surgery when national guidance recommends surgery within 5 days. A better approach would be to test platelet function in people who take clopidogrel to guide timing of surgery and reduce unnecessary delays. PFTs cost in the region of £20- £50 per patient, which is considerably less than the cost of complications of surgery or delays to surgery (thousands of pounds).
This was a simple study in which we took a small sample of blood from participants who were regularly taking clopidogrel and analysed the blood to assess its effect on their platelet function. The study did not involve any intervention, only a blood test. No adverse effects were seen.
Results
The average age of participants was 68yrs, two-thirds of them were male (67%) reflecting the higher prevalence of PAD in males. We found that in a high proportion of participants clopidogrel was not working as well as expected; this phenomenon is known as clopidogrel resistance. Clopidogrel resistance was found by both analysers (Multiplate and TEG 6S) in two-thirds (67 & 72%) of participants in this study.
We found what is considered to be an acceptable rate of similarity between the two types of measurement used (the Multiplate ®method and the TEG®6S method). Most of the time, whichever POC test was used, the test result gave the same answer to the question ‘is there resistance to clopidogrel and could we proceed with surgery and anaesthesia’. There were no occasions where one test gave a result meaning higher risk of clotting whilst the other gave a result meaning higher risk of bleeding, this is very reassuring. This means that we can use either method to test platelet function with a reasonable expectation of getting the same result. Results from this study have helped us to develop a clinical guide to aid decision making about timing of urgent surgery and anaesthesia in people who have been taking clopidogrel.
Patients were not informed of their individual test results according to the study protocol. Test results were occasionally shared with the vascular team caring for the patient if specifically requested. Members of the research were not privvy to any decisions made by surgeons based on these results.
Next Steps
We hope to do further work in this area to evaluate how well the clinical decision aid works in practice and looking at any correlation between platelet function test results and any complications after surgery and anaesthesia.
The Sussex Peri-Operative Research Team would like to thank everyone who participated in this study which has enabled us to learn more about the platelet function testing machines available to aid our clinical decision-making. We would also like to thank the Vascular Anaesthesia Society for their support in funding this study.
The full manuscript will soon be submitted to the British Journal of Anaesthesia in anticipation of publication. Participants who agreed they wanted to receive a copy of the results when they consented to the study will be sent this lay summary. If participants would like to receive a copy of the full manuscript submitted for publication, they can request this by email to vanessa.fludder@nhs.net.
This lay results summary has been reviewed by the UHSussex Research Champions, including members of the public, patients and patient representatives.
REC name
London - Fulham Research Ethics Committee
REC reference
19/LO/1172
Date of REC Opinion
11 Oct 2019
REC opinion
Further Information Favourable Opinion