Blood transfusion explained: reasons, process and risks

In a blood transfusion, blood or blood components are administered via a vein to compensate for a deficiency, for example in the event of blood loss

Text in simple language Our content is pharmaceutically and medically tested

Everything is encrypted: every blood unit can be traced back

© W & B / Fotolia

Briefly explained: blood transfusion

  • Blood or blood components given via an infusion
  • can be done with foreign blood or autologous blood
  • usually only comprises a portion of the total blood
  • is often only used from a certain blood deficiency (anemia)
  • requires the consent of the patient

When is a blood transfusion necessary?

A healthy body replaces smaller blood losses with the increased formation of new blood. But in the event of greater blood loss, these compensation options of the body are no longer sufficient at some point. This can be the case, for example, in the event of an injury or an operation. Long-term (chronic) blood loss can also make a blood transfusion necessary. This is the case with some tumor diseases or with blood formation disorders, for example leukemia. When a blood transfusion is necessary depends not only on the amount of blood lost, but also on the individual health of the person concerned. For example, people with heart disease tend to have problems more quickly after they have lost blood.

How does the blood transfusion work?

Blood transfusions are medical activities. This means that only medical staff are allowed to decide on the gift and then carry it out themselves. Clarification must be given before a blood transfusion. All risks are also mentioned here. At the end you confirm with a signature that you agree to a transfusion. Due to emergencies it can happen that one could not actively consent before the blood transfusion. In these cases, too, a so-called safety explanation takes place afterwards so that those affected know what to look out for if a problem arises.

Then, with every donation of foreign blood, it is ensured that the blood groups of the donor match those of the recipient. Only blood that is tolerated may be given, as otherwise life-threatening defense reactions against the donor blood can occur. The so-called cross match also takes place before the transfusion. Blood from the blood supply is mixed with a blood sample from the recipient. If there is clumping in the sample, this means an intolerance and the blood reserve must not be given. In order to avoid mixing up blood reserves, the so-called bedside test is also carried out immediately before the transfusion. Here, the tolerance is tested one last time directly on the patient (“next to the bed”). The correct identity is also checked one last time, so you should not be confused if you are asked for your name and date of birth shortly before the gift. A vein access is required before the blood transfusion is started. This small plastic tube can be placed directly in front of it. The blood transfusion is done like a normal infusion - the blood drips from a bag into the vein. Monitoring is necessary during the transfusion and for at least half an hour.

A finished blood bag with all the important data

© Panthermedia / Vaximilian

What is a blood bag?

As a rule, the blood supply does not contain whole blood, i.e. not all of the blood, but only the portions that are required.

These can be the following components of the blood:

  • red blood cells (erythrocytes)
  • white blood cells (granulocytes)
  • Blood platelets (thrombocytes)
  • Blood fluid (plasma or plasma components)

The transfusions are called erythrocyte concentrate, granulocyte concentrate, thrombocyte concentrate or fresh frozen plasma. Depending on the size and amount of the cells contained, the concentrates contain 200 to 300 milliliters.

Before donating blood, all people who donate blood receive an examination to determine whether they are suitable for donation. The laboratory tests the donated blood preparations again for possible pathogens.

Platelet concentrates are waiting to be used

© W & B / Valerie Till

When is autologous blood donation an option?

There is donation of blood from others and autologous blood donation. When donating blood from another person, the blood comes from someone stranger; when donating blood from someone else's own blood, it is taken from the person being treated in advance. The autologous blood donation takes place before planned operations, in which the probability is over ten percent that a blood transfusion will be necessary. This can be the case, for example, in cardiovascular operations or major general surgical operations. However, it takes some time to prepare the donated blood until it can be stored as a preserve. The blood must be drawn three to six weeks before the operation. This is then stored as a blood reserve and can be used in the event of major blood losses during the operation. Donating your own blood reduces the risk of intolerance and the risk of infection.

Blood transfusion risks, side effects, and complications

Every blood transfusion comes with risks. The need for a transfusion must therefore always be carefully weighed against the risks involved. Some of the most common complications are explained here:

Minor complications

This could include bruising or infection at the injection site. Blood clots (thromboses) can also form. Occasionally people react to cell and protein components from the donor blood

  • fever
  • malaise
  • chills

Transfusion reaction

A dreaded complication of blood transfusions is the transfusion incident when blood group incompatible with blood is administered. For example, a person with blood group A receives blood with blood group B. The immune system can then react against the donor blood with the destruction of numerous red blood cells, a process known as hemolysis. There is a risk of circulatory shock, kidney failure and blood clotting disorders. A transfusion reaction can occur immediately or delayed for up to two weeks after the transfusion.

infection risk

Despite strict legal regulations in the Transfusion Act and careful examination of the donated blood preparations, it cannot be ruled out with absolute certainty that pathogens are passed on during the blood transfer. These include, for example, hepatitis viruses, which can cause liver inflammation, and HI viruses, which can lead to AIDS. Due to the high safety standard, the risk of infection with blood transfusions in Germany has become extremely low. For example, it is significantly less than 1 in 1 million for the transmission of hepatitis C or HIV, so it is very unlikely.

Allergic reaction

Allergic reactions to a blood transfusion can range from an itchy rash to an allergic shock with circulatory and respiratory failure.


The formation of antibodies against transferred blood components can in rare cases lead to intolerance reactions or a loss of efficacy when re-transfusions are carried out.

Iron deposits

In people who receive many red blood cell (packed) red blood cell transfusions, iron, also known as hemosiderosis, can build up in the liver, pancreas, and heart. It has an adverse effect on the affected organs.

Dr. Christof Weinstock

© W & B / private

Consulting expert: Dr. med. Christof Weinstock, Head of the Blood Group Serology and Immunohematology Department at the Institute for Clinical Transfusion Medicine and Immunogenetics in Ulm.

Important NOTE:
This article contains general information only and should not be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor. Unfortunately, our experts cannot answer individual questions.