Red blood cells, also known as RBCs, red cells, red blood corpuscles, haematids, erythroid cells or erythrocytes (from Greek erythros for "red" and kytos for "hollow vessel", with -cyte translated as "cell" in modern usage), are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the body's capillaries.
The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. The cell membrane is composed of proteins and lipids, and this structure provides properties essential for physiological cell function such as deformability and stability while traversing the circulatory system and specifically the capillary network.
In humans, mature red blood cells are flexible and oval biconcave disks. They lack a cell nucleus and most organelles, in order to accommodate maximum space for hemoglobin; they can be viewed as sacks of hemoglobin, with a plasma membrane as the sack. Approximately 2.4 million new erythrocytes are produced per second in human adults. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Each circulation takes about 60 seconds (one minute). Approximately a quarter of the cells in the human body are red blood cells. Nearly half of the blood's volume (40% to 45%) is red blood cells.
Packed red blood cells (pRBC) are red blood cells that have been donated, processed, and stored in a blood bank for blood transfusion.
Since an RBC count is performed as part of
a complete blood count (CBC), results from other components are taken into
consideration. A rise or drop in the RBC count must be interpreted in
conjunction with other tests, such as haemoglobin, haematocrit, reticulocyte
count, and/or red blood cell indices.
Test |
Reference
Range |
Examples
of Causes of Low Result |
Examples
of Causes of High Result |
Red Blood Cell Count (RBC) |
Conventional Units Men: 4.5-5.9 x 106/microliter Women: 4.1-5.1 x 106 microliter Men: 4.5-5.9 x 1012/L Women: 4.1-5.1 x 1012/L |
Known as anaemia
|
Known as polycythemia
|
Some causes of a low RBC count (anaemia)
include:
·
Trauma that leads to loss of blood
·
Conditions that cause red blood cells to be destroyed, such as
haemolytic anaemia caused by autoimmunity or defects in the red cell itself;
the defects could be a hemoglobinopathy (e.g., sickle cell anaemia),
thalassemia, an abnormality in the RBC membrane (e.g., hereditary
spherocytosis), or enzyme defect (e.g., G6PD deficiency).
·
Sudden (acute) or chronic bleeding from the digestive tract (e.g.,
ulcers, polyps, colon cancer) or other sites, such as the bladder or uterus (in
women, heavy menstrual bleeding, for example)
·
Nutritional deficiency such as iron deficiency or vitamin B12 or folate
deficiency
·
Bone marrow damage (e.g., toxin, radiation or chemotherapy, infection,
drugs)
·
Bone marrow disorders such as leukaemia, multiple myeloma,
myelodysplastic syndrome, or lymphoma or other cancers that spread to the bone
marrow
·
Chronic inflammatory disease or condition
·
Kidney failure—severe and chronic kidney diseases lead to decreased production
of erythropoietin, a hormone produced by the kidneys that promote RBC
production by the bone marrow.
`Some causes of a high RBC count
(polycythemia) include:
·
Dehydration—as the volume of fluid in the blood drops, the count of RBCs
per volume of fluid artificially rises.
·
Lung (pulmonary) disease—if someone is unable to breathe in and absorb
sufficient oxygen, the body tries to compensate by producing more red blood
cells.
·
Congenital heart disease—with this condition, the heart is not able to
pump blood efficiently, resulting in a decreased amount of oxygen getting to
tissues. The body tries to compensate by producing more red blood cells.
·
Kidney tumour that produces excess erythropoietin
·
Smoking
·
Genetic causes (altered oxygen sensing, abnormality in haemoglobin
oxygen release)
·
Polycythemia vera—a rare disease in which the body produces too many
RBCs
Published on 2 June 2019