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What is a red blood cell (RBC)?

Red blood cells are the most abundant cells in the blood. They give blood its characteristic red color. Men have an average of 5,200,000 red blood cells per cubic millimeter. Women have an average of 4,600,000 red blood cells per cubic millimeter. Red blood cells account for about 40 to 45 percent of the blood. The actual percentage of red blood cells is frequently measured and is called the hematocrit. Normally, the ratio of cells in the blood is 600 red blood cells for each white blood cell and 40 platelets.

Red blood cells have several factors that make them unusual:

  • They have a strange shape - a biconcave disc (round and flat, sort of like a shallow bowl).
  • They have no nucleus. The nucleus leaves the cell as it matures.
  • They can change their shape to an amazing extent without breaking. This occurs as the cells squeeze single file through the capillaries.
  • They contain hemoglobin, a special molecule designed to hold oxygen and carry it to cells.

Red blood cells (RBCs) are perhaps the most recognizable component of whole blood. RBCs contain hemoglobin, a complex iron-containing protein that carries oxygen through the body and gives blood its red color. The percentage of blood volume composed of red blood cells is called the “hematocrit.” There are about one billion red blood cells in two to three drops of blood, and for every 600 red blood cells, there are about 40 platelets and one white cell. Manufactured in the bone marrow, RBCs are continuously produced and broken down. They live for about 120 days in the circulatory system. RBCs are prepared from whole blood by removing plasma, or the liquid portion of the blood, and they are used to treat anemia while minimizing an increase in blood volume. Improvements in cell preservation solutions over several decades have increased the shelf-life of RBCs from 21 to 42 days. RBCs may be treated and frozen for extended storage of up to 10 years.

William Lee Dubois
Endocrinologist

Red blood cells (RBCs) are FedEx trucks. They are highly specialized cells whose job is to deliver oxygen from the lungs to every cell in your body and to pick up packages of carbon dioxide to take back to the lungs to exhale.

Cool RBC facts:

  • Red blood cells aren’t actually “proper” cells at all. The adult ones have no nuclei or organelles (crudely put brains and guts), unlike almost all other living cells.
  • Red blood cells don’t divide to reproduce themselves. They are “built” in the bone marrow inside your skeleton.
  • Every day your body produces 100 billion new red blood cells. That’s an ounce of blood, by the way. (You produce 2 million per second, I’m told.)
  • Baby red blood cells are blue.
  • By cell standards, RBCs are small. A single RBC contains 250 million hemoglobin molecules. Each hemoglobin molecule can transport 4 molecules of oxygen. All that math adds up to each RBC can carry a billion oxygen molecules.
  • RBCs look like miniature flying saucers, but they are more pancake than Frisbee. They can twist, turn, and even roll themselves up like burritos to get through capillaries smaller than they are.
  • RBCs don’t use oxygen themselves. Crazy!
  • Women have a lower red blood cell count than men do.
  • When oxygen rich, a red blood cell is described as “scarlet or ruby red.” When low on oxygen the cell is dark red.
  • The life span of a red blood cell is 120 days. Slightly longer than a mosquito.

Red blood cells (RBCs) are cells in the blood that carry oxygen to every part of the body. Bone marrow makes RBCs, and RBCs make hemoglobin. RBCs have instructions (genes) that tell them how to make hemoglobin. RBCs stay in the bone marrow until they’re fully grown. When they’re big enough and have all their hemoglobin, RBCs head out into the bloodstream to deliver oxygen to the body. When the RBCs are worn out they get pulled out of the bloodstream by the spleen. This happens when RBCs are about 120 days old. The spleen recycles all the worn out RBCs. The hemoglobin made by the RBCs is recycled. The body keeps the good parts and gets rid of the junk. Hemoglobin gets broken down into pieces that go back to the blood.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.