Anemia is caused due to low amounts of haemoglobin in blood. Hemoglobin is a protein that carries oxygen in blood to the different tissues.
Three main mechanisms of anemia
There are three main mechanisms that produce anemia. These include –
- Excessive blood loss
- Decreased production of RBCs
- Excessive destruction of RBCs
Causes of anemia
Causes may vary within each of these mechanisms. (1-7)
Anemia due to excessive blood loss
Bleeding due to a surgery or injury when in excess may lead to anemia.
A problem with the blood's clotting ability like in patients with haemophilia may also cause excessive bleeding and lead to anemia.
Further a slow and long term blood loss like in intestinal bleeding from inflammatory bowel disease (IBD) or bowel cancer can also cause anemia.
In many cases a bleeding from stomach ulcer may be a cause for iron deficiency anemia.
Stomach ulcers that belled may be caused by pain relievers called Nonsteroidal anti-inflammatory drugs (NSAIDs) like Aspirin, Ibuprofen etc.
In women heavy menstrual periods may be a cause for blood loss and anemia. Excessive blood loss leads to iron deficiency anemia.
Decreased production of RBCs
This may occur in aplastic anemia. This is a condition where the bone marrow is incapable of making enough RBCs. This could be due to a viral infection, or exposure to certain toxic chemicals, radiation, or medications (such as antibiotics, antiseizure drugs, or cancer treatments).
Apstic anemia may be caused by some childhood cancers like leukemia as well as some chronic diseases that affect the ability of the bone marrow to make blood cells.
Anemia may commonly occur in babies. Before birth the baby is provided with high levels of oxygen from the mother hemoglobin and RBCs via the placenta that connects the baby with the mother.
After the child is born hemoglobin level normally drops to a low point at about 2 months of age. This is called physiologic anemia of infancy. This usually corrects by itself without treatment as the infant's body soon starts making RBCs on its own.
Deficiency of iron in the diet leads to decreased RBC production. This iron-deficiency anemia is the commonest cause of anemia.
Iron is essential to hemoglobin production. Iron deficiency anemia may be caused due to poor dietary iron intake or excessive loss of iron from the body. Girls during puberty who are just beginning to have menstrual periods are at risk of excessive blood loss and iron deficiency anemia.
Excessive Destruction of RBCs
This group of conditions are called haemolytic anemias. Hemolytic anemia occurs when RBCs are destroyed prematurely.
Normally an RBC lives 120 days. As the duration shortens the bone marrow becomes incapable of keeping up with the body’s needs, this leads to anemia.
Hemolytic anemias may be inherited, for example due to thalassemia, glucose-6-phosphate dehydrogenase (G6PD) deficiency and sickle cell anemia.
Sickle cell anemia is a severe form of anemia found most commonly in people of African heritage.
About 1 out of every 625 African-American children is born with this form of anemia. In this the hemoglobin forms long rods when it gives up its oxygen and make the RBCs sickle in shape. This leads to premature destruction of RBCs, chronically low levels of haemoglobin and anemia.
Thalassemia usually affects people of Mediterranean, African, and Southeast Asian heritage. Here the haemoglobin is abnormal resulting in abnormal and short-lived RBCs. The destroyed RBCs lead to increased iron deposition in the skin and vital organs.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency also affects males of African heritage.
In this the RBCs either do not make enough of the enzyme G6PD or the enzyme that is produced is abnormal and dysfunctional. Certain stress or medications may lead to massive destruction of RBCs in people with this deficiency.
Certain conditions lead to increased risk of anemia
This includes pregnancy where there is increased demand for RBCs and iron. Those with Chronic kidney disease, rhematroid arthritis, inflammatory disorders also develop iron deficiency anaemia.
Other conditions like oesophagitis, stomach ulcers, schistosomiasis (an infection caused by parasites) or other parasitic infections like hookworm infections, blood donation and some cancers may lead to anemia.
Diabetics are commonly affected with kidney disease. Damaged kidneys may not produce enough erythropoietin (EPO), a hormone that regulates red blood cell production. This could lead to anemia.
Malabsorption occurs when the body is unable to absorb nutrients like iron, vitamin B12 and folates needed for health haemoglobin and RBC formation. Malabsorption may be seen in coeliac disease or after surgical removal of part of the stomach or intestines.
Vitamin B12 deficiency and folate deficiency may result from dietary deficiency as well as in certain autoimmune conditions.
Pernicious anaemia is the most common cause of vitamin B12 deficiency in the UK.
Pernicious anaemia is an autoimmune condition. This means the immune system attacks the body’s own cells.
Normally Vitamin B12 is absorbed using a protein called intrinsic factor that attaches to the dietary vitamin B12 and allows it to be absorbed from the stomach.
Pernicious anaemia leads to the destruction of this intrinsic factor by the body’s immune system. Vitamin B12 and folate deficiency is seen commonly in pregnant women and in the elderly.
Edited by April Cashin-Garbutt, BA Hons (Cantab)
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