Editing Red blood cell (section)

==Clinical significance==

=== Disease ===
[[Image:Sicklecells.jpg|frame|right|Affected by [[Sickle-cell disease]], red blood cells alter shape and threaten to damage internal organs.]]

[[Blood diseases]] involving the red blood cells include:
* [[Anemia]]s (or anaemias) are diseases characterized by low oxygen transport capacity of the blood, because of low red cell count or some abnormality of the red blood cells or the hemoglobin.

:* [[Iron deficiency anemia]] is the most common anemia; it occurs when the dietary intake or absorption of iron is insufficient, and hemoglobin, which contains iron, cannot be formed.

:* [[Pernicious anemia]] is an [[autoimmune disease]] wherein the body lacks [[intrinsic factor]], required to absorb [[vitamin B12|vitamin B<sub>12</sub>]] from food. Vitamin B<sub>12</sub> is needed for the production of red blood cells and hemoglobin.

:* [[Sickle-cell disease]] is a genetic disease that results in abnormal hemoglobin molecules. When these release their oxygen load in the tissues, they become insoluble, leading to mis-shaped red blood cells. These sickle shaped red cells are less deformable and [[Blood Viscoelasticity|viscoelastic]], meaning that they have become rigid and can cause blood vessel blockage, pain, strokes, and other tissue damage.

:* [[Thalassemia]] is a genetic disease that results in the production of an abnormal ratio of hemoglobin subunits.

:*[[Hereditary spherocytosis]] syndromes are a group of inherited disorders characterized by defects in the red blood cell's [[cell membrane]], causing the cells to be small, sphere-shaped, and fragile instead of donut-shaped and flexible. These abnormal red blood cells are destroyed by the [[spleen]]. Several other hereditary disorders of the red blood cell membrane are known.<ref>{{cite journal | vauthors = An X, Mohandas N | title = Disorders of red cell membrane | journal = British Journal of Haematology | volume = 141 | issue = 3 | pages = 367–375 | date = May 2008 | pmid = 18341630 | doi = 10.1111/j.1365-2141.2008.07091.x | s2cid = 7313716 }}</ref>

:* [[Aplastic anemia]] is caused by the inability of the [[bone marrow]] to produce blood cells.

:* [[Pure red cell aplasia]] is caused by the inability of the bone marrow to produce only red blood cells.

[[Image:Osmotic pressure on blood cells diagram.svg|thumb| right|Effect of [[osmotic pressure]] on blood cells]]
[[File:Human Erythrocytes OsmoticPressure PhaseContrast Plain.svg|thumb|right|Micrographs of the effects of osmotic pressure]]
* [[Hemolysis]] is the general term for excessive breakdown of red blood cells. It can have several causes and can result in [[hemolytic anemia]].

:* The [[malaria]] parasite spends part of its life-cycle in red blood cells, feeds on their hemoglobin and then breaks them apart, causing fever. Both [[sickle-cell disease]] and [[thalassemia]] are more common in malaria areas, because these mutations convey some protection against the parasite.
* [[Polycythemia]]s (or erythrocytoses) are diseases characterized by a surplus of red blood cells. The increased viscosity of the blood can cause a number of symptoms.

:* In [[polycythemia vera]] the increased number of red blood cells results from an abnormality in the bone marrow.
* Several [[microangiopathy|microangiopathic diseases]], including [[disseminated intravascular coagulation]] and [[thrombotic microangiopathies]], present with [[pathognomonic]] (diagnostic) red blood cell fragments called [[schistocyte]]s. These pathologies generate [[fibrin]] strands that sever red blood cells as they try to move past a [[thrombus]].

=== Transfusion ===
{{main|Blood transfusion}}
Red blood cells may be given as part of a [[blood transfusion]]. Blood may be [[blood donation|donated]] from another person, or stored by the recipient at an earlier date. Donated blood usually requires [[screening (medicine)|screening]] to ensure that donors do not contain risk factors for the presence of blood-borne diseases, or will not suffer themselves by giving blood. Blood is usually collected and tested for common or serious [[blood-borne disease]]s including [[Hepatitis B]], [[Hepatitis C]] and HIV. The [[blood type]] (A, B, AB, or O) or the blood product is identified and matched with the recipient's blood to minimise the likelihood of [[acute hemolytic transfusion reaction]], a type of [[transfusion reaction]]. This relates to the presence of [[antigen]]s on the cell's surface. After this process, the blood is stored, and within a short duration is used. Blood can be given as a whole product or the red blood cells separated as [[packed red blood cells]].

Blood is often transfused when there is known anaemia, active bleeding, or when there is an expectation of serious blood loss, such as prior to an operation. Before blood is given, a small sample of the recipient's blood is tested with the transfusion in a process known as [[cross-matching]].

In 2008 it was reported that human [[embryonic stem cell]]s had been successfully coaxed into becoming red blood cells in the lab. The difficult step was to induce the cells to eject their nucleus; this was achieved by growing the cells on [[stromal cell]]s from the bone marrow. It is hoped that these artificial red blood cells can eventually be used for blood transfusions.<ref>{{Cite web| vauthors = Coghlan A |date=2008-08-19 |title=First red blood cells grown in the lab|url=https://www.newscientist.com/article/dn14565-first-red-blood-cells-grown-in-the-lab/|access-date=2023-03-26|website=New Scientist|language=en-US}}</ref>

A human trial is conducted in 2022, using blood cultured from stem cells obtained from donor blood.<ref>
{{ Cite web
 | url          = https://www.medicalnewstoday.com/articles/researchers-are-trialing-lab-grown-blood-transfusions-what-to-know#Transfusing-lab-made-red-blood-cells
 | title        = Researchers are trialing lab-grown blood transfusions: What to know
 | website      = medicalnewstoday.com
 | date = 11 November 2022
 | publisher    = MedicalNewsToday
 | access-date  = 2022-11-17
 | url-status   = live
 | language     = en
 | archive-url  = https://web.archive.org/web/20221115050210/https://www.medicalnewstoday.com/articles/researchers-are-trialing-lab-grown-blood-transfusions-what-to-know
 | archive-date = 2022-11-15
 | quote        = A team of researchers led by the National Health Service (NHS) Blood and Transplant unit recently launched the first clinical trial to transfuse lab-grown red blood cells into a live human.
}}
</ref>

=== Tests ===
[[File:Poikilocytes - Red blood cell types.jpg|thumb|Variations of red blood cell shape, overall termed [[poikilocytosis]]]]
Several [[blood test]]s involve red blood cells. These include a ''RBC count'' (the number of red blood cells per volume of blood), calculation of the [[hematocrit]] (percentage of blood volume occupied by red blood cells), and the [[erythrocyte sedimentation rate]]. The [[blood type]] needs to be determined to prepare for a [[blood transfusion]] or an [[organ transplantation]].

Many diseases involving red blood cells are diagnosed with a [[blood film]] (or peripheral blood smear), where a thin layer of blood is smeared on a microscope slide. This may reveal [[poikilocytosis]], which are variations in red blood cell shape. When red blood cells sometimes occur as a stack, flat side next to flat side. This is known as ''[[rouleaux]] formation'', and it occurs more often if the levels of certain serum proteins are elevated, as for instance during [[inflammation]].

=== Separation and blood doping ===
Red blood cells can be obtained from [[whole blood]] by [[centrifugation]], which separates the cells from the [[blood plasma]] in a process known as [[blood fractionation]]. [[Packed red blood cells]], which are made in this way from whole blood with the plasma removed, are used in [[transfusion medicine]].<ref>{{cite web|url=http://www.aabb.org/resources/bct/Documents/coi0809r.pdf|title=Circular of Information for Blood and Blood Products|publisher=American Association of Blood Banks, American Red Cross, America's Blood Centers|access-date=1 November 2010|url-status=dead|archive-url=https://web.archive.org/web/20111030212757/http://www.aabb.org/resources/bct/Documents/coi0809r.pdf|archive-date=30 October 2011}}</ref> During [[blood donation|plasma donation]], the red blood cells are pumped back into the body right away and only the plasma is collected.

Some athletes have tried to improve their performance by [[blood doping]]: first about 1&nbsp;litre of their blood is extracted, then the red blood cells are isolated, frozen and stored, to be reinjected shortly before the competition. (Red blood cells can be conserved for 5 weeks at {{convert|−79|C|F|disp=or}}, or over 10 years using cryoprotectants<ref>{{cite book | vauthors = Valeri CR | chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK233117/| chapter = Frozen Red Cell Technology| veditors = Sparacino L, Manning FJ | title = Blood Groups and Red Cell Antigens |date=8 February 1996|publisher=National Academies Press (US)|via=www.ncbi.nlm.nih.gov}}</ref>) This practice is hard to detect but may endanger the human [[cardiovascular system]] which is not equipped to deal with blood of the resulting higher [[viscosity]]. Another method of blood doping involves injection with [[erythropoietin]] to stimulate production of red blood cells.  Both practices are banned by the [[World Anti-Doping Agency]].