Blood carries oxygen and nutrients through your blood vessels to your organs to keep them healthy. Without enough blood, you'll feel sick and might even die.
Blood is made up of different types of cells and a liquid called plasma.
The different types of cells include:
Plasma is mainly water. It carries minerals (electrolytes) and nutrients to all the tissues in your body. It also carries useful proteins your body makes, such as those that help your blood clot or help fight off infection. Plasma also receives waste products from your tissues and delivers them to the kidneys to be eliminated in urine.
A blood transfusion is when blood donated by other people is given to you through an IV (a tube in your vein).
Doctors rarely give transfusions of whole blood. Usually the lab separates out the different parts of blood so you can be transfused with only what you need. For example, you may just get:
But there are different blood types. If you need a transfusion, you need to get blood that matches your type.
Red blood cells have two main chemical markers on their surface. The markers are called A and B. Your blood type is determined by which of those markers are on your red blood cells:
There's also an Rh marker. If you have it, your blood type is "positive" (+). If you don't have the Rh marker, your blood type is "negative" (-). So, for example, you could be type A+ or A-.
A volunteer donates about a pint (450 mL) of blood at a time. The blood is sent to a blood bank for storage.
Before people donate blood, they have to answer questions to make sure their blood is safe to give to other people. They're asked about countries they've visited and behavior that could have put them at risk for certain diseases. Such diseases include hepatitis and HIV infection. After blood is donated, it's tested for certain infections. Testing makes blood transfusion very safe, although it can't eliminate all possible risk.
Sometimes, you can donate blood for yourself. For example, if you're scheduled for surgery that could involve a lot of bleeding, your doctor may have you donate your own blood a few weeks before the surgery. Then until the surgery, you'll take iron pills to help your body make more blood. If you need blood during the surgery, the doctor can transfuse your own blood.
Blood transfusions usually don't cause problems because health care providers giving the blood transfusion take precautions to keep you safe. When people do have problems, most of them are mild, but they can be serious.
The most serious, but very rare, side effects are:
Getting too much fluid, which can cause difficulty breathing
Damage to your lung that can make it hard to breathe
Breakdown of red blood cells because the blood type in the transfusion doesn't match yours—this can cause dark urine and a yellow color in the white part of your eye
Infections from viruses or bacteria in the donated blood
The most common side effects are fever and allergic reactions.
You may have itching, rash, swelling, dizziness, headache, chest pain, back pain, and fast heart beat
Sometimes you may also have breathing trouble, wheezing, or urinating (peeing) without meaning to
Doctors will stop the transfusion and give you an allergy medicine that relieves itching and lowers swelling
For any future transfusions, they may filter the donated blood to lower your chance of an allergic reaction
Before your transfusion, health care providers will:
During the transfusion, health care providers will: