Red blood cells, Opens dialog

Immune system, Opens dialog

Test Overview

Coombs tests are done to find certain antibodies that attack red blood cells. Antibodies are proteins made by the immune system. Normally, antibodies bind to foreign substances, such as bacteria and viruses, and cause them to be destroyed.

The following conditions cause antibodies to be made.

Transfusion reaction

Human blood is typed by certain markers (called antigens) on the surface of red blood cells (Figure 1). If you get a blood transfusion, the transfused blood must match your type. That means the transfused blood must have the same antigens as your red blood cells. If you get a transfusion of blood with antigens different from yours (incompatible blood), your immune system (Figure 2) destroys the transfused blood cells. This is called a transfusion reaction and can cause serious illness or even death. This is why matching blood type is so important.

Rh sensitization

Rh is an antigen. The full name for this antigen is Rhesus factor.

If a pregnant woman with Rh-negative blood is pregnant with a baby (fetus) with Rh-positive blood, Rh sensitization may occur. The baby may have Rh-positive blood if the father has Rh-positive blood. Rh sensitization happens when the baby's blood mixes with the mother's blood during pregnancy or delivery. This causes the mother's immune system to make antibodies against the baby's red blood cells in future pregnancies. This antibody response is called Rh sensitization and, depending on when it happens, can destroy the red blood cells of the baby before or after it is born. If sensitization happens, a fetus or newborn can develop mild to severe problems (called Rh disease or erythroblastosis fetalis). In rare cases, if Rh disease is not treated, the fetus or newborn may die.

A woman with Rh-negative blood can get a shot of Rh immunoglobulin (such as WinRho) that almost always stops sensitization from occurring. Problems from Rh sensitization have become very rare since Rh immunoglobulin was developed.

Autoimmune hemolytic anemia

A type of hemolytic anemia called autoimmune hemolytic anemia is a rare disease that causes antibodies to be made against a person's own red blood cells.

Two blood tests can check for antibodies that attack red blood cells: the direct Coombs test and the indirect Coombs test. The direct Coombs test is done on a sample of red blood cells from the body. It detects antibodies that are already attached to red blood cells. The indirect Coombs test is done on a sample of the liquid part of the blood (serum). It detects antibodies that are present in the bloodstream and could bind to certain red blood cells, leading to problems if blood mixing occurs.

Figure 1 - Red blood cells

The red blood cells carry oxygen to the body's tissues and remove carbon dioxide and other wastes.

Current as of: December 13, 2023

Author: Ignite Healthwise, LLC Staff
Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

Figure 2 - Immune system

The immune system is the body's natural defence system that helps fight infections. The immune system includes the following.

The tonsils.

These are on either side of the back of the throat. The tonsils help make antibodies.

The thymus gland.

This is found in the upper chest at the bottom of the neck, behind the breastbone. The thymus also helps make antibodies.

Bone marrow.

This is soft tissue that is found mainly inside the long bones of the arms and legs, the vertebrae, and the pelvic bones. The marrow makes white blood cells that destroy bacteria, viruses, and other organisms that cause infection.

The spleen.

This organ is found in the upper left side of the abdomen. It filters the blood by removing old or damaged blood cells and platelets. The spleen helps the immune system by destroying bacteria and other foreign substances.

Lymph nodes and vessels (the lymphatic system).

This system is found throughout the body. It carries fluid, nutrients, and waste material between the body tissues and the bloodstream. The lymph nodes filter lymph fluid as it flows through them. The nodes trap bacteria, viruses, and other foreign substances, which are then destroyed by special white blood cells. These cells are called lymphocytes.

Current as of: September 25, 2023

Author: Ignite Healthwise, LLC Staff
Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.