See how a clot forms at a vessel injury, and how anticoagulant medication intervenes to prevent dangerous blockages.
Anticoagulants — often called blood thinners — are medicines that reduce the blood's ability to form clots. They do not literally thin the blood, but interrupt key steps in the clotting cascade, making it harder for dangerous clots to develop inside blood vessels.
They are prescribed to people at elevated risk of harmful clots forming in veins or arteries. Left untreated, these clots can travel to the lungs (pulmonary embolism), brain (stroke), or heart, with potentially fatal consequences. Anticoagulants are highly effective — but they require careful, ongoing monitoring to keep you safe.
A long-established anticoagulant that works by blocking Vitamin K, which is essential to the clotting process. Because many factors alter its effect — including diet, other medicines, and illness — it requires regular INR blood tests to ensure the dose is correctly calibrated.
Newer agents — including apixaban, rivaroxaban, edoxaban and dabigatran — work differently from warfarin. They generally have a more predictable effect and do not require routine INR monitoring, but patients still need regular GP review to ensure continued safety.
Anticoagulation is prescribed for several conditions where there is an increased risk of dangerous blood clot formation.
AF causes an irregular heart rhythm, which can allow clots to form in the heart and travel to the brain, causing a stroke. Anticoagulation significantly reduces this risk.
Deep vein thrombosis (DVT) and pulmonary embolism (PE) are treated and prevented with anticoagulation, both acutely and as long-term prophylaxis where ongoing risk remains.
Patients with mechanical prosthetic valves must take warfarin long-term. The artificial valve creates turbulent flow which increases clotting risk — lifelong anticoagulation is essential.
Following a TIA (mini-stroke) or ischaemic stroke, anticoagulation may be prescribed to reduce future stroke risk, particularly in patients with underlying conditions such as AF.
After major surgery — especially hip and knee replacements — short-term anticoagulation prevents DVT and PE during recovery, when mobility is limited.
This autoimmune condition causes the blood to clot more readily than normal. Long-term anticoagulation is typically required to prevent recurrent thrombotic events.
We run a dedicated nurse-led clinic for patients who are already established on warfarin and classed as clinically stable. Appointments are efficient, friendly, and focused on keeping you safe.
Your INR is measured via a simple finger-prick or venous draw to check your warfarin is working within your therapeutic range.
Our trained nurse reviews your result and adjusts your warfarin dose if needed, following established clinical protocols and consulting your GP where required.
Your next monitoring appointment is scheduled before you leave. Frequency depends on stability — typically every 4–12 weeks for stable patients.
This clinic is for established, stable warfarin patients. Those newly starting warfarin, or with unstable INR readings, may initially be managed via the hospital anticoagulation service before transferring to us.
INR (International Normalised Ratio) measures how long your blood takes to clot relative to a normal sample. The ideal target range depends on your condition:
| Condition | Target INR |
|---|---|
| Atrial Fibrillation | 2.0 – 3.0 |
| DVT / Pulmonary Embolism | 2.0 – 3.0 |
| Mechanical Valve (aortic) | 2.0 – 3.0 |
| Mechanical Valve (mitral) | 2.5 – 3.5 |
| Antiphospholipid Syndrome | 2.0 – 3.0 |
INR above target increases bleeding risk. Contact the surgery promptly if you notice unusual bruising, prolonged bleeding, or blood in your urine or stools.
INR below target means insufficient protection against dangerous clots. Do not skip or delay your monitoring appointments.
Recent changes to prescribing guidance mean we can no longer issue anticoagulant prescriptions without first confirming that monitoring is up to date.
Anticoagulants can be dangerous if not carefully monitored. To protect patient safety, GPs must now confirm that required monitoring has been completed before any prescription is issued.
To ensure you can receive your prescription without delay, please ensure the following:
Suddenly stopping anticoagulation can dramatically increase your risk of stroke, DVT, or pulmonary embolism. Request your repeat prescription at least 5–7 days before your supply runs out. If you are concerned about running out, call us immediately on 0208 574 5136.
Anticoagulants are safe and effective when taken correctly and monitored regularly. Here is what every patient on anticoagulation should know.
Contact the surgery or call 999/NHS 111 urgently if you experience any of the following:
Always inform your doctor, pharmacist, and dentist that you take anticoagulants before starting any new medication or undergoing a procedure.
Available 24 hours a day, 365 days a year — free from all landlines and mobiles. For urgent medical advice when your GP is closed, including concerns about your anticoagulation.
Dial 999 immediately for severe uncontrolled bleeding, symptoms of stroke (facial drooping, arm weakness, speech difficulty), chest pain, or any life-threatening emergency.