The Facts

Blood carries oxygen and nutrients to the tissues and organs and removes waste products. It is made up of several main components, including red blood cells, white blood cells, platelets, and plasma. Red blood cells carry and release oxygen throughout the body. White blood cells are part of your immune system and help fight infection. Platelets help the blood form clots, which stops bleeding.

Blood cells are suspended in a watery, yellowish liquid called plasma, which also contains proteins partly responsible for blood clotting and globulins that help fight infection and disease.

There are approximately 4 L to 5 L of blood in the body. Losing large amounts of blood quickly can lead to serious complications or death. Severe blood loss is usually treated with a transfusion or transfusion alternatives such as medications.


There are many possible causes of blood loss. Accidents, surgery, childbirth, stomach ulcers, and blood vessel rupture can cause a sudden loss of blood. In addition, illnesses such as cancer and leukemia often result in lower-than-normal numbers of blood cells. Some conditions, such as heavy menstrual bleeding, cause a gradual blood loss over a long period of time.

Although all types of blood loss may cause complications, it is the large and rapid blood losses that occur during surgery and trauma that are most likely to cause severe complications or death. The amount of blood loss that may lead to complications depends on the individual person. It is affected by factors such as body size and the presence of certain health conditions (e.g., anemia).

A person's risk of blood loss severe enough to require a transfusion during surgery depends on a number of factors, including health status (conditions such as hemophilia increase the risk of bleeding) and medications or herbs they may be taking (blood thinners such as warfarin* can increase the risk of bleeding).

Symptoms and Complications

The effects of blood loss depend on a person's general state of health, the amount of blood lost, and how quickly it was lost. Bleeding may be internal or external. With external bleeding, blood leaves the body through a break in the skin (from a wound, trauma, or surgery), or a body opening such as the mouth, anus, or vagina. With internal bleeding, blood is lost from the blood vessels, but stays inside the body, often leading to swelling and pain. Both internal and external bleeding can lead to serious complications. Internal bleeding may be harder to recognize and diagnose because the bleeding is not visible.

The more blood is lost, and the faster it is lost, the more severe the symptoms and complications.

The symptoms of blood loss include:

  • abdominal pain or swelling (a symptom of internal bleeding)
  • bleeding during surgery
  • bleeding from the mouth
  • blood coming from a break in the skin
  • blood coming from the vagina (unexpectedly, or much more than expected)
  • blood in the stool (the stool may be black and tarry or red)
  • blood in the urine (the urine may be pink, red, or brownish in colour)
  • bruising (a bruise forms when there is blood under the skin)
  • cool, clammy skin
  • dizziness, weakness, or confusion
  • fast, weak pulse
  • paleness
  • trouble breathing
  • vomiting blood or material that looks like coffee grounds

The complications of blood loss are related to the role blood plays in the body (see above). If too much blood volume is lost, a condition known as hypovolemic shock can occur. Hypovolemic shock is a medical emergency in which severe blood and fluid loss impedes the heart to pump sufficient blood to the body. As a result, tissues cannot get enough oxygen, leading to tissue and organ damage. If left untreated, this condition can be fatal. Complications can be more serious in people taking blood thinners or those with bleeding disorders.

Making the Diagnosis

Doctors diagnose blood loss based on signs and symptoms, medical history, and lab tests. In some cases, such as trauma and surgery, the presence and cause of blood loss will be obvious. Otherwise, the doctor may also check for other conditions such as bleeding stomach ulcers. Doctors may also ask about recent medications or herbs they may have taken that might contribute to bleeding. Depending on the suspected cause of bleeding, blood tests may be needed.

Treatment and Prevention

Treatment of blood loss focuses on two areas: stopping the bleeding and treating the effects of blood loss. The techniques used to stop bleeding depend on the cause and location of the bleeding. For external bleeding such as cuts and tears, direct pressure followed by bandaging or stitching can be used. For internal bleeding, surgery may be needed.

Treatment for the effects of blood loss depends on how much blood was lost; how quickly it was lost; and the person's medical conditions, medications, and religious beliefs. For mild blood loss, treatment with fluids and medications is often enough. For more severe blood loss, a blood transfusion or transfusion alternative is often needed. Some groups, such as Jehovah's Witnesses, will not accept transfusions for religious reasons.

Before the transfusion, the recipient (the person getting the transfusion) has their blood tested. Blood and blood products from a compatible donor (matched according to blood type and other factors) are given through a vein by injection. Blood transfusions usually involve giving the blood components (such as red blood cells or platelets) that a person is lacking.

Like any medical procedure, a blood transfusion has risks. Blood transfusion risks include:

  • transfusion reactions: If donor blood is not properly matched to the blood type of the recipient, or if blood is given to the wrong person by mistake, severe illness may result, including hemolysis (breakdown of red blood cells), kidney damage, and even death. The risk of incompatible blood type transfusion is about 1 in 14,000.
  • infectious disease: Even though the blood supply is thoroughly screened, there is still a small risk of getting a viral (including HIV, hepatitis, and West Nile virus), bacterial, or parasitic infection from a blood transfusion. The risk of contracting HIV from a blood transfusion is less than 1 in 21 million. The risk of getting hepatitis C is less than 1 in 12 million.
  • allergic reactions: Allergic reactions to the transfused blood may be mild and easily treated, or severe and potentially leading to death. The risk of a serious allergic reaction is about 1 in 40,000.

When receiving health care, a person must be informed and agree to a treatment before treatment can be given.

Since all medical therapy involves some degree of risk, patients make decisions about their treatment after weighing the risks and benefits of their options. This is called informed consent or informed choice. Any "competent" patient (a person who has the mental capacity to make their own treatment decisions, including an understanding of what may happen if they do not accept the suggested treatment) may refuse a treatment a doctor recommends, including blood transfusion.

Blood shortages and increased awareness of the risks associated with blood transfusions have spawned much research over the last decade into alternatives to blood transfusions. Today, there are a number of alternatives to blood transfusions. Blood transfusions can be minimized or avoided by using appropriate combinations of medications, medical devices, and surgical techniques. Many hospitals around the world now have blood conservation or bloodless medicine and surgery programs.

Medications can be used to stimulate the body to produce more blood cells. Erythropoietin is used to increase the body's production of red blood cells. G-CSF (granulocyte colony stimulating factor) and GM-CSF (granulocyte macrophage colony stimulating factor) are used to increase white blood cells. Other medications can be used to reduce bleeding during or after surgery or sudden blood loss. Special fluids such as pentastarch, saline, or Ringer's lactate can be used to temporarily replace the lost blood volume.

Devices such as blood salvage ("cell saver") machines can help reduce blood loss during surgery by collecting blood lost during surgery, processing it, and returning it to the patient. Specialized scalpels can cut through tissue and stop bleeding at the same time (by using heat, electric current, or ultrasonic vibration).

Surgical techniques and pre-surgery planning can also reduce blood loss. Large surgeries may be divided into several small ones, and new techniques such as laparoscopy reduce the need for large incisions. In pre-surgery planning, medications that increase the risk of bleeding are stopped or reduced before surgery, and other medications are taken to build up the body's reserve of blood cells. Some people choose to donate and store their own blood before an operation. In other cases, a technique called hypotensive anesthesia can be used to reduce surgical bleeding.

Not all of these transfusion alternatives will be available or appropriate for everyone. Like transfusions, transfusion alternatives also have risks. The risks and benefits of any treatment option will vary for each individual person. Before any treatment is chosen, it is important you and your doctor to review the options carefully.

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