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Information for Surgical Patients

Information about Blood Transfusions

During the course of surgery, a patient may require a blood transfusion. This page contains information about the nature of blood transfusions, risks associated with them, and who to contact for more information.

What is a blood transfusion?
Why might I need a transfusion?
What is blood made up of?
What other options do I have?
What are the risks if I do not have a transfusion?
What are the risks if I have a transfusion?
What to tell us before the transfusion
How do I know if I am having a reaction?
After I leave the hospital
Important documents

What is a blood transfusion?

A blood transfusion is a medical procedure that gives you components of blood that your body needs to stay healthy.

You get a transfusion through a needle inserted into a vein. The transfusion can take anywhere from one to four hours.

Why might I need a transfusion?

You may need a transfusion if:

  • you have lost blood due to surgery, trauma, gut or stomach bleeding, or other conditions
  • you are anemic (you have a low red blood cell count)
  • your platelets or clotting factors are low or not working properly.

What is blood made up of?

The main parts of blood that may be given by transfusion are:

Red blood cells

Red blood cells are filled with hemoglobin, which carries oxygen to the body’s tissues and organs and helps keep them healthy. You may need a red blood cell transfusion to have more oxygen delivered to your tissues and organs.


Platelets are small cells that help prevent or stop bleeding. You may need a platelet transfusion if you do not have enough platelets or if they do not work properly.

Plasma and cryoprecipitate (Cryo)

Plasma and cryoprecipitate contain many substances, such as clotting factors. You may need a plasma or cryoprecipitate transfusion if your clotting factors are low.

Other blood products

Other blood products are sometimes needed, but only in special situations. Some examples are:

  • Immune globulins(Ig) such as RhIg, Intravenous Ig (IVIg), Subcutaneous Ig (SCIg), Hepatitis B Ig
  • Albumin
  • Clotting factor concentrates
  • Specific protein concentrates

Your health care provider will discuss these with you if you are likely to need them.

What other options do I have?

There may be other options to transfusion available to you. Ask your health care provider about these options.

What are the risks if I do not have a transfusion?

Ask your doctor or health care provider what the risks are if you do not have a transfusion. Different blood components and products are given for different reasons.

For example, if you lose too many red blood cells, your body will not get enough oxygen. Without enough oxygen, there is the risk of damage to important organs such as the brain or heart. Or, if your platelets are low, then you may be at risk for bleeding.

The timing and reason for needing a transfusion is different from person to person. The decision to give you blood will be based on your condition at that time.

Your health care team will always compare the benefits to the risks before using blood for any reason. Used properly, blood can save your life.

What are the risks if I have a transfusion?

Most transfusions are problem free. In some cases, reactions may occur. The risks from transfusion include:

  • Allergic reactions: These are usually mild and easy to treat. Severe allergic reactions are extremely rare.
  • Fever: These common reactions are usually not severe and resolve with treatment.
  • Hemolytic reactions: These are rare. They would occur if your blood destroys the transfused red blood cells from the donor blood. These reactions can sometimes be severe, and may cause bleeding or kidney failure.
  • Infectious diseases: Blood is collected by Canadian Blood Services from volunteer donors. These donors are screened before they can donate blood to make sure they are suitable to donate.
    • All donor blood is tested for specific infectious diseases.
    • The risk of infection caused by viruses, parasites or bacteria that may be transmitted by transfusion is very small. However, the tests cannot take away the risk of infection entirely.

The table below shows some of the risks of a blood transfusion. The larger the number in the column on the right side (your chances), the lower the risk that a transfusion will cause the problem listed on the left.

For example, the risk of infection with HIV (1 in 10,000,000) is much lower than the risk of infection with Hepatitis B (1 in 2,000,000).

Disease Your chances (risk per unit)
Infectious risks
HIV 1 in 21,400,000*
Hepatitis C (HCV) 1 in 12,600,000*
Hepatitis B (HBV) 1 in 7,500,000*
HTLV 1 in 7,600,000**
West Nile Virus Less than 1 in 1,000,000**
Bacterial sepsis 1 in 100,000 platelet pools***
1 in 250,000 red blood cells**
Non-infectious risks
Fluid overload 1 in 100**
Hives, itchiness (minor allergic) 1 in 100**
Fever 1 in 300**
Delayed hemolytic reaction 1 in 31,800****
Acute hemolytic reaction 1 in 77,407**


* O’Brien SF, et al.Residual risk of HIV, HCV and HPV in Canada. Transfuse Apheresis Sci (2017),
** Callum JL et al. Bloody Easy4 (2016). 4th Ed., p. 42-45
*** Ramirez-Arcos S et al. Residual risk of bacterial contamination of platelets: six years of experience with sterility testing.
**** Transfusion Transmitted Injuries Surveillance System (TTISS summary results for 2009-2013)

What to tell us before the transfusion

Please tell your health care team if:

  • you had a reaction to a previous transfusion. Some reactions can be prevented by giving medication before the transfusion.
  • you were told that you need special blood because you have a rare blood type, have antibodies or because of your condition.

How do I know if I am having a reaction?

A reaction can occur during a transfusion, a day after the transfusion, or even up to a few weeks after the transfusion.

While you are in the hospital, your nurse will monitor you during the transfusion for a reaction. If you have a reaction, the transfusion may need to be stopped.

Please let your nurse know right away if you have any of the following signs or symptoms:

  • bleeding, pain, or new bruising where the IV was put in
  • severe back pain
  • fever, chills
  • nausea, vomiting
  • rash, hives, itching
  • headache, dizziness
  • cold, clammy skin
  • chest pain
  • fast heartbeat, palpitations
  • trouble breathing, wheezing
  • dark or reddish urine
  • yellowing of the skin or eyes

After I leave the hospital

Watch for any of the symptoms that you may be having a reaction to the blood transfusion. If you notice any of these signs or symptoms:

  • contact your family doctor or St. Michael's doctor or nurse immediately
  • call 911 or go to the nearest Emergency Room

Important documents

Wallet card

If we find that you need special blood, you will get a wallet card on discharge.

  • Keep this wallet card on you at all times and show it to your health care provider.

Letter from the hospital

After you leave the hospital, we will send you a letter if you received a transfusion during your hospital stay. This letter is for information only. Keep this letter with your medical records, and feel free to share it with your family doctor.


The phone number at St. Michael’s Hospital is 416-864-6060. For more information, you can talk to:

  • Your doctor, surgeon, nurse practitioner or nurse
  • Patient blood management coordinators, extension 6733 or 3036
  • Transfusion safety nurse, extension 6732
  • Transfusion Medicine (laboratory), extension 5084
  • Your family doctor