Can recent surgery cause a blood clot? 

Undergoing surgery is a significant physical event that triggers the body’s natural healing and protective mechanisms. While these processes are essential for recovery, they also involve changes in how the blood clots. Recent surgery is one of the most common risk factors for developing a blood clot, known medically as a venous thromboembolism (VTE). 

This article explores the biological reasons why the risk of clotting increases after an operation, which procedures carry the highest likelihood of complications, and how the medical team works to keep you safe. By understanding the signs of a clot and the importance of post-operative movement, you can play an active role in your own recovery and long-term health. 

What We’ll Discuss in This Article 

• The biological link between surgical trauma and blood ‘stickiness’. 

• Why immobility during and after surgery affects circulation. 

• High-risk procedures, including orthopaedic and abdominal surgeries. 

• Common triggers that can lead to a post-operative clot. 

• Differentiation between normal surgical swelling and a DVT. 

• Proactive steps and medical tools used for clot prevention. 

How Surgical Procedures Increase the Risk of Blood Clots 

Yes, recent surgery is a well-recognised cause of blood clots, particularly Deep Vein Thrombosis (DVT) and pulmonary embolism (PE). The risk is elevated because surgery often involves three specific factors: damage to blood vessel walls, a natural increase in the blood’s ability to clot to prevent bleeding, and periods of immobility. This combination makes it easier for a thrombus to form in the deep veins, usually in the legs. 

The risk of a clot is highest in the first few weeks following a procedure, but it can remain elevated for up to three months. Hospital-acquired clots are a serious concern, which is why clinical guidelines from NICE and the NHS mandate a VTE risk assessment for every patient admitted for surgery. 

• Tissue Factor Release: During surgery, the body releases substances that activate the ‘clotting cascade’ to seal off damaged vessels. 

• Anesthesia Impact: General anesthesia causes blood vessels to relax and blood pressure to drop, which can slow down the speed of blood flow. 

• The 90-Day Window: While many think the danger ends when they leave the hospital, a significant portion of surgical clots occur after discharge. 

Clinical context shows that without preventative measures, certain surgeries, such as hip or knee replacements, carry a very high natural risk of clotting due to the extensive manipulation of bone and surrounding tissue. 

Causes of Post-Operative Clotting 

The increase in clotting risk is primarily driven by the body’s systemic response to trauma. Even a planned, successful surgery is interpreted by the body as an injury that needs to be ‘plugged’ to prevent haemorrhage. 

Specific causes include: 

• Endothelial Damage: The physical act of cutting or moving tissues can damage the lining of the veins, creating a ‘rough’ surface where platelets can easily catch and clump. 

• Hypercoagulability: The liver increases the production of clotting proteins like fibrinogen in response to the inflammation caused by surgery. 

• Venous Stasis: When you are under anesthesia or resting in bed, the ‘calf muscle pump’ which usually pushes blood back up to the heart is inactive, causing blood to pool. 

Triggers for Clots Following Surgery 

Beyond the surgery itself, several triggers can increase the likelihood of a clot forming during the recovery phase. Managing these triggers is a key part of post-operative care. 

• Prolonged Bed Rest: Staying in bed for long periods without moving the legs is the single most common trigger for a post-surgical clot. 

• Dehydration: If a patient is unable to drink well after surgery, or loses fluid through wound drainage, the blood becomes more concentrated and thicker. 

• Infection: Post-operative infections, such as a chest infection or wound site infection, trigger widespread inflammation that encourages clotting. 

• Underlying Health Profiles: Patients who smoke, have a high BMI, or have active cancer are at a higher baseline risk when surgery acts as an additional trigger. 

Differentiation: Surgical Healing vs. Blood Clot 

After surgery, some swelling, bruising, and discomfort are expected at the site of the operation. However, it is vital to distinguish these normal healing signs from the symptoms of a DVT. 

Feature	Normal Post-Surgical Healing	Deep Vein Thrombosis (DVT)
Location	Swelling is usually at the incision site or involves both legs mildly.	Swelling is usually in one leg and involves the whole calf or thigh.
Pain Level	Expected soreness that improves with prescribed painkillers.	A new, throbbing, or cramping pain, often starting in the calf.
Skin Colour	Some bruising or pinkness around the incision.	The skin may turn red, blue, or a dusky purple colour.
Vein Appearance	Veins look normal.	Surface veins may look swollen or more prominent than usual.
Breathlessness	Not a feature of normal wound healing.	Sudden breathlessness or chest pain (signs of a PE).

Conclusion 

In summary, recent surgery is a major risk factor for blood clots due to the combination of physical trauma, changes in blood chemistry, and reduced mobility. Fortunately, modern surgical teams use a variety of tools from blood-thinning injections to compression stockings to mitigate this risk. The most important thing a patient can do is follow the mobilization plan provided by their physiotherapist and stay well-hydrated. 

If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

You may find our free BMI Calculator helpful for understanding how your weight profile might influence your recovery and vascular risk after surgery. 

Authority Snapshot (E-E-A-T Block) 

This article was reviewed by Dr. Rebecca Fernandez, a UK-trained physician with extensive experience in general surgery, intensive care, and emergency medicine. Dr. Fernandez has hands-on experience in stabilising acute trauma cases and managing the complex post-operative needs of critically ill patients. This guide provides evidence-based information to help patients navigate the recovery process safely and identify potential vascular complications early.