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Red Blood Cells Explained


Mrs Kayon Lee 

Biomedical Scientist

Red blood cells (RBCs), also called erythrocytes, are cells that circulate in the blood and carry oxygen throughout the body. The RBC count totals the number of red blood cells that are present in a person’s sample of blood. It is one test among several that is included in a complete blood count (CBC) and is often used in the general evaluation of a person’s health.

Blood is made up of a few different types of cells suspended in fluid called plasma. In addition to RBCs, there are white blood cells (WBCs) and platelets. These cells are produced in the bone marrow and are released into the bloodstream as they mature. RBCs typically make up about 40% of the blood volume. RBCs contain haemoglobin, a protein that binds to oxygen and enables RBCs to carry oxygen from the lungs to the tissues and organs of the body. RBCs also help transport a small portion of carbon dioxide, a waste product of cell metabolism, from those tissues and organs back to the lungs where it is expelled.

The typical lifespan of an RBC is 120 days; thus the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding. There are a number of conditions that can affect the production of new RBCs and/or their lifespan, in addition to those conditions that may result in significant bleeding. These conditions may lead to a rise or drop in the RBC count. The normal range in men is approximately 4.7 to 6.1 million cells/ul (microliter). The normal range in women range from 4.2 to 5.4 million cell/ul, according to the National Institute of Health data.

Changes in the RBC count usually mirror changes in the haematocrit and haemoglobin level. Haemoglobin is a protein in the red blood cells that carries oxygen and gives blood its red colour. When the values of the RBC count, haematocrit, and haemoglobin decrease below the established reference interval, the person is said to be anaemic. When the RBC and haemoglobin values increase above the normal range, the person is said to be polycythaemia. Too few RBCs can affect the amount of oxygen reaching the tissues, while too many RBCs can cause decreased blood flow and related problems.



July 2018

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