Reasons you may be taking an oral anticoagulant

More and more people require life-long oral anticoagulation (Vitamin K Antagonists, also called coumarin derivatives) as a result of various medical conditions described in detail below.

Sine everyone reacts differently to these drugs and many interferences exist such as diet, stress, other drugs, etc., the periodic measurement of Prothrombin Time (PT) or International Normalized Ratio (INR) is the test performed to adjust dosage of oral anticoagulation therapies to the proper individual "therapeutic range". This therapeutic range will be defined by your doctor or healthcare professional, who will need the PT/INR tests to monitor it.The human body has a complex mechanism called coagulation that causes blood to clot if a wound occurs. Under normal circumstances this is desirable; it allows the body to heal itself. Yet in some clinical conditions, coagulation can cause unwanted blood clots that can be life threatening.

These are some common reasons why a blood clot forms and why an anticoagulant may be prescribed:

  • Atrial fibrillation (irregular heartbeat)
  • Mechanical or artificial heart valves – can cause a "foreign body" reaction.
  • Deep Vein Thrombosis (DVT) – slow-moving or stationary blood in a vein deep within a muscle of the leg or pelvis. (blood clot)
  • Heart attack causing damage to heart muscle.
  • Stroke

If a blood clot (thrombus) develops due to any of the above causes, there is a risk that it may "break off" and move to another part of the body where it can cause a blockage and further damage.

To read more about these conditions, download our information booklet listed in the right-hand column.

Expand All | Collapse All
Atrial Fibrillation (AF)

Atrial Fibrillation (AF) is a type of cardiac arrhythmia, and it affects over 1 million people in the UK. People with AF have an irregular and uncoordinated heartbeat, which is caused by a disruption to the electrical signal controlling the heart. Those affected, may experience distressing symptoms such as palpitations, tiredness and shortness of breath. Others may experience little to no symptoms at all. Atrial fibrillation can affect people of any age, although it is particularly common in older age people. Untreated or inappropriately managed AF can have life threatening consequences. It can make the heart less efficient at pumping blood around the body causing blood to pool and potentially clot, which means people affected can be more vulnerable to strokes.

Mechanical Heart valve replacement

We all have four valves that control the flow of blood through our hearts. These valves are sometimes weakened after a heart attack, or by high blood pressure, birth defects and severe lung disease. There are approximately 50,000 heart valve replacements in Europe every year, and over 50 per cent of patients have a mechanical heart valve¹.

Deep Vein Thrombosis and Pulmonary Embolism

Venous thromboembolism (VTE) is a term which encompasses both Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE). You will have probably heard of DVT, which is where a blood clot forms in a deep vein, such as in the calf. In some cases, the clot can travel up toward the heart or lungs, and this is commonly known as a pulmonary embolism (PE).

There may be increased risk of DVT under conditions of:

  • Prolonged immobility, for example long journeys where you sit still without being able to stretch your legs or move about
  • A medical condition that restricts normal movement or activity
  • Surgery such as orthopaedic surgery or illness that requires treatment such as chemotherapy
  • Genetic or inherited conditions
  • Existing vein damage from a previous DVT
  • The contraceptive pill and hormone replacement therapy
  • Pregnancy

Some people may only realise they have a DVT when a pulmonary embolism develops as a result of the blood clot in the leg breaking away and being carried to the lungs in the blood stream. Pulmonary Embolism is a very serious condition.

A Pulmonary Embolism (PE) is a blood clot in the lung that usually originates from smaller blood vessels in the leg. A clot from a DVT travels to the lungs and through the vessels of the lung until it reaches smaller vessels where it becomes lodged. The clot then prevents any further blood from travelling to that section of the lung which can eventually lead to stroke.

Common symptoms may include:

  • Chest pain that is sharp and is worse when taking a deep breath
  • Shortness of breath
  • Low blood pressure
  • Sweating
  • Anxiety

All the above can also be symptoms for other conditions; however Pulmonary Embolism can be life threatening so if you are concerned, seek the advice of a doctor or go to your nearest accident and emergency department.

People that experience a PE may be in hospital for several days until their anticoagulant medication is introduced and stabilised. They may remain on anticoagulation therapy for six months or longer.


1. NICE Diagnostics guidance [DG14]. September 2014