Science Facts

How Do Blood Transfusions Work? – Full Process

Blood Transfusion

About every two seconds, someone in the United States needs blood. That is a lot of blood to transfuse from donors to patients. The faults and failures of early transfusions have significantly helped shape how blood transfusion procedures work today. Long before anyone understood blood, scientists knew that blood was a life force flowing through us all.

To harness the power of blood and infuse it into another person, usually someone sick or dying. Patients would usually drink the blood, which of course, did not affect. The idea of a blood transfusion didn’t occur until William Harvey’s 1628 discovery that blood circulates through the body in one direction. It was then that scholars and doctors realized that transfusions were a possible method of rejuvenating the sick.

What is blood transfusion?

A blood transfusion is a standard procedure that involves taking blood from one person, the donor, and giving it to a person who requires more blood. The most common reason for a blood transfusion is to address a shortage of red blood cells in the blood. Red blood cells are necessary for carrying oxygen around the body. Sometimes this happens because the bone marrow which produces red blood cells can’t make enough of them.

When is a patient transfused? It depends on what’s going on with the patient, their vital signs, and how they tolerate that low blood level. Recent guidelines by the American Association of blood banks recommend transfusing blood when hemoglobin levels fall to 7 to 8 grams per deciliter.

Normal hemoglobin level:

  • Male, 14 to 18 grams per deciliter.
  • In females, it’s 12 to 16 grams per deciliter.

How do blood transfusions work?

Blood carries oxygen and nutrients to tissues and removes carbon dioxide and other waste products from them. It also helps fight infection and heal wounds. Blood consists of a liquid portion and cellular components. The liquid called plasma is where nutrients, hormones, clotting factors, and other chemicals are dissolved. The cellular components are suspended in the plasma.

  • They consist of red blood cells which transport oxygen and carbon dioxide.
  • White blood cells fight infection.
  • Platelets are small subcells that help the blood clot.

Blood cells are made in the bone marrow, a soft tissue housed inside many bones. A blood transfusion uses donor blood to replenish:

  • Red blood cells.
  • White blood cells.
  • Platelets.
  • Clotting factors.
  • Plasma.

Whole blood circumstances may require a blood transfusion include:

  • Blood loss due to trauma.
  • Heart or other major surgery.
  • Organ transplants.
  • Bleeding disorders such as Hemophilia.
  • Severe anemia, including sickle cell Anemia.
  • Treatment for leukemia or other types of cancer.
  • Disorders that destroy blood cells or bone marrow.
  • Rh incompatibility in newborn babies.

A bag containing the donor blood will be hung nearby to begin the transfusion, and the intravenous needle inserted into a vein in the hand or arm. The blood will drip slowly through a tube attached to the IV needle allowing it to run through the vein into the bloodstream. The donor’s body temperature, heart rate, breathing, and blood pressure will be monitored throughout the transfusion.

After the bag is empty, another bag will be attached to the IV tube if the patient requires more blood. When the transfusion is completed, the needle will be removed. After transfusion doctor will monitor vital signs to make sure not to have an adverse reaction. For emergency, the patient may be given a diuretic to reduce any swelling or fluid retention.

By the end of the 17th century, physicians used quills as needles and silver pipes to transfer blood from a donor to a recipient. But the donor was usually an animal. No one knew at the time was animal blood cells are incompatible with human blood. It wasn’t until obstetrician James Blundell started using human blood to replace blood lost in childbirth in the early 1800s. That transfusion began working, at least some of the time.

Physician Karl Landsteiner set out to figure out why some blood transfusion patients lived and others died. A line of inquiry led him to discover the ABO blood type groups in 1901. Landsteiner’s groundbreaking work helped classify blood into four categories: A, B, AB, and O. the antigens and antibodies define these on the cells.

People with type A blood, for example, have the A antigen on the surface of their red cells. And their bodies won’t produce the anti-A antibodies. So if any type A blood is introduced into that person’s body, it won’t recognize the new cells as foreign and won’t attack them. But if type B blood is injected into a type A blood person, the anti-B antibodies on the donated blood will be seen as foreign. The host’s body will reject the transfusion.

Another factor for rejection comes down to a protein on the surface of red blood cells called the Rhesus or Rh factor. Blood cells either possess the protein. It means that Rh is positive or negative. These factors combine to make eight blood types. Now all of this is important because blood type determines compatibility with a donor. The red blood cells of people with type O blood have A or B antigens on their surface, making them universal donors. People with type AB blood don’t produce any antibodies. So they are universal recipients. But everyone else is only compatible with their specific type.

So knowing what we’ve learned over centuries of trial and error, blood transfusions have become simpler. There’s no need for a living donor. Instead, donated red blood cells can be stored for as long as 42 days. It means a patient in need is given an IV and a bag of blood to replenish what they’re missing or restore blood lost in an accident.

Blood transfusion procedure

A blood transfusion is a straightforward procedure that a nurse carries out. At first, Donar will need to sign a consent form. Before blood transfusion, a nurse or doctor will go through with this. They can ask as many questions as they like. A nurse or doctor will take a small blood sample to check the blood type. Donors must be given blood that’s compatible with the receiver’s blood type. So donors must be correctly identified at each stage of the blood transfusion.

Then donors will be asked to state their full name and date of birth. When they have their blood transfusion, some people will be given a card to say that they can only get specific blood types.

Donar can be sitting up or lying down during transfusion and at roughly 15-minute intervals throughout the transfusion. The blood is usually given through a tiny tube called an intravenous line inserted directly into a vein in the arm using a fine needle. The insertion may cause slight discomfort for a moment, but the donor shouldn’t feel anything during the transfusion. It may take up to four hours to give the patient each bag of blood.

However, this can be safely speeded up when necessary or if it’s urgent. The patient may be given more than one bag of blood as part of your treatment. Blood transfusions are very safe, and it has many benefits. Donate your blood and save a life.

More Articles:


“Blood Transfusion | National Heart, Lung, and Blood Institute (NHLBI).”
Adams RC, Lundy JS. “Anesthesia in cases of poor surgical risk. Some suggestions for decreasing risk”.
“Five Things Physicians and Patients Should Question,” Choosing Wisely: an initiative of the ABIM Foundation, American Association of Blood Banks.

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