Taking blood thinners before, during, and after surgery

A blood thinner is a medicine used to prevent or treat blood clots. There are two main types of blood thinners, anticoagulants and antiplatelet agents. While they both prevent blood from clotting, or more precisely, slow the formation of clots, they work in different ways.


Anticoagulant drugs work by interfering with normal blood clotting factors circulating in the body. This makes it harder for the blood to clot and increases the time it takes for the body to successfully form a clot.

Anticoagulants are more aggressive than antiplatelet drugs, so this type of drug is used when a patient requires the blood to be “thinned”.

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Antiplatelet drugs work by interfering with the chemical “signals” that the body sends out when it needs to form a clot. Typically, the signal activates platelets, a type of blood cell debris that clumps at the bleeding site and starts sticking together to form a clot.

With antiplatelet drugs in circulation, the propagation of the signal is delayed and the “volume” is turned down, so platelets decrease.

Why use blood thinners?

Surgery is a known risk factor for thrombosis, as patients are often at rest for extended periods of time during surgery and for hours or days after surgery. Immobility is a known risk factor for thrombosis, so thrombosis prevention is an important part of perioperative surgical care.

For some patients, blood thinners are used to thin the blood, which makes it take longer for the blood to clot. In other patients, blood thinners are used to prevent existing clots from getting worse (and prevent additional clots from forming).

A blood test determines if blood thinners are needed and the dose that should be given.

Some patients require prolonged use of blood thinners, such as those with a cardiac arrhythmia called atrial fibrillation. For others, such as patients who have recently had surgery, they may have blood thinning during the hospital stay but no longer need it.

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Before surgery

Blood thinners can be tricky before surgery. Surgeons must find a balance between preventing blood clots and allowing patients to bleed too much during surgery.

For some patients who routinely take blood thinners before surgery, the usual daily dose of blood thinners is stopped at least 24 hours and up to a week before surgery.

This brief interruption is usually sufficient to prevent excessive bleeding without significantly increasing the risk of blood clots.

However, if coumarin (warfarin) is used, it is stopped 5 to 7 days before surgery and transitioned to a short-acting drug like Lovenox. This requires extensive planning by both the patient and the surgeon.

Blood thinners can then be resumed the day after surgery, assuming blood tests show it to be appropriate.

During surgery

Blood thinners are medicines that are not usually used during surgical procedures unless there are special circumstances that make the use of blood thinners beneficial to the patient, such as the use of a heart-lung bypass machine.

Blood thinners do increase bleeding during surgery, so when blood loss is an expected part of surgery, this must be taken into account before giving such drugs.

after surgery

Blood thinners are often used after surgery to prevent blood clots in the legs, called deep vein thrombosis (DVT) and other types of blood clots. Blood clots should always be taken seriously because one blood clot can turn into many, or a blood clot in the leg can move and become a blood clot in the lungs.

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Hearts that don’t beat at their normal rhythm can also cause blood clots to form, which can lead to strokes, Therefore, monitor blood clots closely for best results.

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test thin blood

There are three blood tests used to test blood for clotting. These tests are called prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR).

You may also hear these tests called “clotting studies,” “clotting time,” or “PTPTTINR” because they’re usually ordered together.

common blood thinners

The most commonly used blood thinning drugs are as follows:

  • aspirin
  • Coumarin/Warfarin
  • heparin
  • Love Knox
  • Plavix

The choice of blood thinner is usually made by the surgeon, who is most likely to know how much bleeding to expect during a particular procedure. Depending on the nature of the disease and the procedure, they may want to inhibit clotting slightly, or they may need to significantly reduce the likelihood of clotting.

Usually, after surgery, heparin is injected into the abdomen 2 to 3 times a day. In some cases, Lovenox is used instead of heparin, but in the vast majority of cases, one or the other is used during recovery in the hospital.

Blood thinners may or may not be prescribed for patients who are discharged immediately after surgery because the patient is expected to walk throughout the day, which greatly reduces the risk of blood clots.

VigorTip words

If you have concerns about receiving blood thinners or are unsure why you should be receiving blood thinners, be sure to talk to your healthcare team.

Blood clots can be a serious risk in some surgeries and less common in others, meaning blood thinners may or may not be necessary for you, depending on The nature of your surgery and your state of health.

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These drugs do carry risks, but the risk of blood clots may be higher in some cases.

Frequently Asked Questions

  • Do blood thinners lower blood pressure?

    No, blood thinners do not lower blood pressure. However, because everyone can respond to medications differently, it’s important to let your healthcare provider know about each medication you take.

  • What are the side effects of blood thinners?

    Potential side effects of blood thinners may include bleeding, upset stomach, diarrhea, and nausea. Other side effects will depend on the type of medication being taken. If you experience any of these side effects while using blood thinners, call your healthcare provider right away.

  • What happens when you stop taking blood thinners?

    Depending on how long the effects of the drug last, your risk of developing blood clots increases when you stop taking blood thinners. There is a greater risk of thromboembolic events, such as deep vein thrombosis, within the first 90 days of stopping warfarin therapy.

  • Can a blood clot develop while taking blood thinners?

    Yes, you can get blood clots while using blood thinners. However, this can only happen if the dose you dispense is too small. On the other end of the spectrum, taking too much blood thinner can cause bleeding. Doctors who prescribe blood thinners do regular blood tests to make sure everyone’s dose is right for them.

  • How long does blood thinner stay in your system?

    How long blood thinners stay in your system depends on the type of medication you are taking. For example, after you stop warfarin, the drug may continue to work for two to five days.