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Anemia (AmE)) or anaemia (BrE), from the Greek meaning "without blood", is a deficiency of red blood cells and/or hemoglobin. This results in a reduced ability of blood to transfer oxygen to the tissues, causing hypoxia; since all human cells depend on oxygen for survival, varying degrees of anemia can have a wide range of clinical consequences. Hemoglobin (the oxygen-carrying protein in the red blood cells) has to be present to ensure adequate oxygenation of all body tissues and organs.

The three main classes of anemia include excessive blood loss (acutely such as a hemorrhage or chronically through low-volume loss), excessive blood cell destruction (hemolysis) or deficient red blood cell production. In menstruating women, dietary iron deficiency is a common cause of deficient red blood cell production.

Anemia is the most common disorder of the blood. There are several kinds of anemia, produced by a variety of underlying causes. Anemia can be classified in a variety of ways, based on the morphology of RBCs, underlying etiologic mechanisms, and discernible clinical spectra, to mention a few.

Different clinicians approach anemia in different ways; two major approaches of classifying anemias include the "kinetic" approach which involves evaluating production, destruction and loss, and the "morphologic" approach which groups anemia by red blood cell size. The morphologic approach uses a quickly available and cheap lab test as its starting point (the MCV). On the other hand, focusing early on the question of production (e.g., via the reticulocyte count) may allow the clinician more rapidly to expose cases where multiple causes of anemia coexist. Regardless of one's philosophy about the classification of anemia, however, any methodical clinical evaluation should yield equally good results.

Symptoms of anemia

Signs and symptoms

Anemia goes undetected in many people, and symptoms can be vague. Most commonly, people with anemia report a feeling of weakness or fatigue. People with more severe anemia sometimes report shortness of breath. Very severe anemia prompts the body to compensate by markedly increasing cardiac output, leading to palpitations and sweatiness; this process can lead to heart failure in elderly people.

Pallor (pale skin and mucosal linings) is only notable in cases of severe anemia, and is therefore not a reliable sign.


The only way to definitively diagnose most cases of anemia is with a blood test. Generally, clinicians order a full blood count. Apart from reporting the number of red blood cells and the hemoglobin level, the automatic counters also measure the size of the red blood cells by flow cytometry, which is an important tool in distinguishing between the causes of anemia. A visual examination of a blood smear can also be helpful in some cases, and is sometimes a necessity in regions of the world where automated analysis is less accessible.

In modern counters, four parameters (RBC Count, hemoglobin concentration, MCV and RDW) are measured, allowing others (hematocrit, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration) to be calculated, and compared to values adjusted for age and sex. For males, the hemoglobin level that is suggestive of anemia is usually less than 13.0 g/dl, and for females, it is less than 12.0 g/dl.

Depending on the clinical philosophy, whether the hospital's automated counter can immediately add it to the initial tests, and the clinicians' attitudes towards ordering tests, a reticulocyte count may be ordered either as part of the initial workup or during followup tests. This is a nearly direct measure of the bone marrow's capacity to produce new red blood cells, and is thus the most used method of evaluating the problem of production. This can be especially important in cases where both loss and a production problem may co-exist. Many physicians use the reticulocyte production index – a calculation of the ratio between the level of anemia and the extent to which the reticulocyte count has risen in response. Even in cases where an obvious source of loss exists, this helps evaluate whether the bone marrow will be able to compensate for the loss, and at what rate.

When the cause is not obvious, clinicians use other tests to further distinguish the cause for anemia. These are discussed with the differential diagnosis, below. A clinician may also decide to order other screening blood tests that might identify the cause of fatigue; serum glucose, ESR, ferritin, serum iron, RBC folate level, serum vitamin B12, renal function tests (e.g. serum creatinine) and electrolytes may be part of such a workup.


The "kinetic" approach to anemia yields what many argue is the most clinically relevant classification of anemia. This classification depends on evaluation of several hematological parameters, particularly the blood reticulocyte (precursor of mature RBCs) count. This then yields the classification of defects by decreased RBC production, increased destruction, or blood loss.

In the morphological approach, anemia is classified by the size of red blood cells; this is either done automatically or on microscopic examination of a peripheral blood smear. The size is reflected in the mean corpuscular volume (MCV). If the cells are smaller than normal (under 80 fl), the anemia is said to be microcytic; if they are normal size (80-100 fl), normocytic; and if they are larger than normal (over 100 fl), the anemia is classified as macrocytic. This scheme quickly exposes some of the most common causes of anemia; for instance, a microcytic anemia is often the result of iron deficiency. In clinical workup, the MCV will be one of the first pieces of information available; so even among clinicians who consider the "kinetic" approach more useful philosophically, morphology will remain an important element of classification and diagnosis.

Other characteristics visible on the peripheral smear may provide valuable clues about a more specific diagnosis; for example, abnormal white blood cells may point to a cause in the bone marrow.

Microcytic anemia

  • iron deficiency anemia is the most common type of anemia overall, and it is often hypochromic microcytic. Iron deficiency anemia is caused when the dietary intake or absorption of iron is insufficient. Iron is an essential part of hemoglobin, and low iron levels result in decreased incorporation of hemoglobin into red blood cells. In the United States, 20% of all women of childbearing age have iron deficiency anemia, compared with only 2% of adult men. The principal cause of iron deficiency anemia in premenopausal women is blood lost during menses. Studies have shown that iron deficiency without anemia causes poor school performance and lower IQ in teenage girls. In older patients, iron deficiency anemia is often due to bleeding lesions of the gastrointestinal tract; fecal occult blood testing, upper endoscopy and lower endoscopy are often performed to identify bleeding lesions, which can be malignant. Iron deficiency is the most prevalent deficiency state on a worldwide basis. Iron deficiency affects women from different cultures and ethnicities. In countries where meat consumption is not as common, iron deficiency anemia is six to eight times more prevalent than in North America and Europe. This is due to the importance of meat in the diets of North Americans and Europeans. A characteristic of iron deficiency is angular chelitis, which is an abnormal fissuring of the angular sections (corners of the mouth) of the lips.
  • hemoglobinopathies -- much rarer (apart from communities where these conditions are prevalent)

Microcytic anemia is primarily a result of hemoglobin synthesis failure/insufficiency, which could be caused by several etiologies:

  • Heme synthesis defect
  • Globin synthesis defect
    • alpha-, and beta-thalassemia
    • HbE syndrome
    • HbC syndrome
    • and various other unstable hemoglobin diseases
  • Sideroblastic defect
    • Hereditary Sideroblastic anemia
    • Acquired Sideroblastic anemia
    • Reversible Sideroblastic anemia

A mnemonic commonly used to remember causes of microcytic anemia is TAILS: T - Thalassemia, A - Anemia of chronic disease, I - Iron deficiency anemia, L - Lead toxicity associated anemia, S - Sideroblastic anemia.

Normocytic anemia

Macrocytic anemia

Macrocytic anemia can be further divided into "megaloblastic anemia" or "non-megaloblastic macrocytic anemia". The cause of megaloblastic anemia is primarily a failure of DNA synthesis with preserved RNA synthesis, which result in restricted cell division of the progenitor cells. The megaloblastic anemias often present with neutrophil hypersegmentation (6-10 lobes). The non-megaloblastic macrocytic anemias have different etiologies (i.e. there is unimpaired DNA synthesis,) which occur, for example in alcoholism.

The treatment for vitamin B12-deficient macrocytic and pernicious anemias was first devised by William Murphy who bled dogs to make them anemic and then fed them various substances to see what (if anything) would make them healthy again. He discovered that ingesting large amounts of liver seemed to cure the disease. George Minot and George Whipple then set about to chemically isolate the curative substance and ultimately were able to isolate the vitamin B12 from the liver. For this, all three shared the 1934 Nobel Prize in Medicine. Symptoms of vitamin B12 deficiency include having a smooth, red tongue.

Dimorphic anemia

Here there are two types of anemia simultaneously, e.g., macrocytic hypochromic, due to hookworm infestation leading to deficiency of both iron and vitamin B12 or folic acid [1] or following a blood transfusion.

Specific anemias

  • Fanconi anemia is an hereditary disease featuring aplastic anemia and various other abnormalities
  • Hemolytic anemia is a separate constellation of symptoms (also featuring jaundice and elevated LDH levels) with numerous potential causes. It can be autoimmune, immune, hereditary or mechanical (e.g. heart surgery). It can result (because of cell fragmentation) in a microcytic anemia, a normochromic anemia, or (because of premature release of immature red blood cells from the bone marrow), a macrocytic anemia.
  • Hereditary spherocytosis is a hereditary disease that results in defects in the RBC cell membrane, causing the erythrocytes to be sequestered and destroyed by the spleen. This leads to a decrease in the number of circulating RBCs and, hence, anemia.
  • Warm autoimmune hemolytic anemia is an anemia caused by autoimmune attack against red blood cells, primarily by IgM

Possible complications

Anemia diminishes the capability of individuals who are affected to perform physical labor. This is a result of one's muscles being forced to depend on anaerobic metabolism. The lack of iron associated with anemia can cause many complications, including hypoxemia, brittle or rigid fingernails, cold intolerance, impaired immune function, and possible behavioral disturbances in children.

Hypoxemia resulting from anemia can worsen the cardio-pulmonary status of patients with pre-existing chronic pulmonary disease. Brittle or rigid fingernails may be a result of abnormal thinness of nails due to insufficient iron supply. Cold intolerance occurs in one in five patients with iron deficiency anemia, and becomes visible through numbness and tingling. Impaired immune functioning leading to increased likelihood of sickness is another possible complications.

Finally, chronic anemia may result in behavioral disturbances in children as a direct result of impaired neurological development in infants, and reduced scholastic performance in children of school age. Behavioral disturbances may even surface as an attention deficit disorder.

Anemia during pregnancy

Anemia affects 20% of all females of childbearing age in the United States. Because of the subtlety of the symptoms, women are often unaware that they have this disorder, as they attribute the symptoms to the stresses of their daily lives. Possible problems for the fetus include increased risk of growth retardation, prematurity, intrauterine death, rupture of the amnion and infection.

During pregnancy, women should be especially aware of the symptoms of anemia, as an adult female loses an average of two milligrams of iron daily. Therefore, she must intake a similar quantity of iron in order to make up for this loss. Additionally, a woman loses approximately 500 milligrams of iron with each pregnancy, compared to a loss of 4-100 milligrams of iron with each period. Possible consequences for the mother include cardiovascular symptoms, reduced physical and mental performance, reduced immune function, tiredness, reduced peripartal blood reserves and increased need for blood transfusion in the postpartum period.

Diet and anemia

Consumption of food rich in iron is essential to prevention of iron deficiency anemia; however, the average adult has approximately nine years worth of B12 stored in the liver, and it would take four to five years of an iron-deficient diet to create iron-deficiency anemia from diet alone.

Iron-rich foods include red meat; green, leafy vegetables; dried beans; dried apricots, prunes, raisins, and other dried fruits; almonds; seaweeds; parsley; whole grains; and yams. In extreme cases of anemia, researchers recommend consumption of beef liver, lean meat, oysters, lamb or chicken, or iron drops may be introduced. Certain foods have been found to interfere with iron absorption in the gastrointestinal tract, and these foods should be avoided. They include tea, coffee, wheat bran, green leafy vegetables, rhubarb, chocolate, soft drinks, red wine, ice cream, and candy bars (Bauer, 2). With the exception of milk and eggs, animal sources of iron provide iron with better bioavailability than vegetable sources (Scrimshaw).

Treatments for anemia

There are many different treatments for anemia, including increasing dietary intake of readily available iron and iron supplementation; the treatment is determined by the type of anemia that is diagnosed. In severe cases of anemia, a blood transfusion may be necessary.


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