Bone marrow is a spongy tissue found in the center of bones that produces bone marrow stem cells and other substances, which in turn produce blood cells. Bone marrow is essential for the production of different types of cells that are vital to sustaining life, including red blood cells, white blood cells, and platelets. Each type of blood cell made by the bone marrow has an important job. Red blood cells carry oxygen to tissues in the body, platelets stop bleeding by helping blood clot, and white blood cells fight infections. Bone marrow also stores fat that turns into energy as needed.

Bone marrow transplants are sometimes necessary after certain treatments, such as high dose chemotherapy and radiation therapy, that treat cancer. These treatments tend to damage healthy stem cells as well as destroy cancer cells. Bone marrow transplants can replace diseased, nonfunctioning bone marrow with healthy functioning bone marrow, regenerate a new immune system that fights existing or residual leukemia or other cancers that chemotherapy or radiation therapy has not killed, and replace bone marrow and restore its usual function after a person receives high doses of chemotherapy or radiation therapy to treat a malignancy.

Bone marrow tests can help diagnose certain conditions, especially those related to blood and blood-forming organs. Testing provides information on iron stores and blood production. Bone marrow aspiration uses a hollow needle to remove a small sample of bone marrow for examination under a microscope. A healthcare professional usually inserts a needle into the hip or sternum in adults or into the upper part of the tibia in children. They use suction to extract the sample.