Anemia (American English) or anaemia (Commonwealth English), which literally means "without blood," is a lack of red blood cells and/or hemoglobin. This results in a reduced ability of blood to transfer oxygen to the tissues. 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 causes of anemia include excessive blood loss (hemorrhage), excessive red blood cell destruction (hemolysis) or 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 is classified according to the size of the red blood cell: decreased (microcytic), normal (normocytic) or enlarged (macrocytic or megaloblastic).


Signs and symptoms

Anemia goes undetected in many people, and symptoms can be vague. Most commonly, a feeling of weakness or fatigue is reported. Shortness of breath is reported in more severe cases. Very severe anemia prompts a compensatory response where cardiac output is markedly increased, 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 diagnose anemia is with a blood test. Generally, a full blood count is done. Apart from reporting the amount of red blood cells and the hemoglobin level, the automatic counters also measure the size of the red blood cells, which is an important tool in distinguishing between the causes.

Occasionally, other tests are required to further distinguish the cause for anemia. These are discussed with the differential diagnosis (below). The doctor may also decide to take some other screening blood tests that might identify the cause of fatigue; glucose levels, ESR, ferritin, renal function tests and electrolytes may be part of such a workup.

Differential diagnosis

Anemia is classified by the size of the 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. 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

The most common type of anemia overall is iron deficiency anemia, which is most often microcytic. Much rarer causes (apart from communities where these conditions are prevalent) are hemoglobinopathies such as sickle cell anaemia and thalassemia.

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 of often due to bleeding lesions of the gastrointestinal tract; fecal occult blood testing, upper 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.

Normocytic anemia

Normocytic anemia can be caused by acute blood loss, chronic disease ("anemia of chronic disease") or failure to produce enough red blood cells (as opposed to hemoglobin, which causes microcytic anemia). Chronic renal failure or liver failure cause normocytic anemia; in renal failure this is due to decreased production of the hormone erythropoietin.

Certain hormonal deficiencies, like testosterone deficiency (hypogonadism), can cause normocytic anemia. Lastly, sideroblastic anemia is caused by abnormal production of red blood cells as part of myelodysplastic syndrome, which can evolve into hematological malignancies (especially acute myelogenous leukemia).

Aplastic anemia (bone marrow failure) is anemia caused by the inability of the bone marrow to produce blood cells. Aplastic anemias are much rarer than dietary deficiency or genetic defect anemias, and progess rapidly.

Macrocytic anemia

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.

Specific anemias

  • Hemolytic anemia is a separate constellation of symptoms (also featuring jaundice and elevated LDH levels) with numerous potential causes. It can be autoimmune, 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.

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 functioning, 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 subtleness 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, reduces 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. These 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. Certain foods have been found to interfere with iron absorption in the gastrointestnal tract, and these foods should be avoided. They include tea, coffee, wheat bran, spinach, rhubarb, chocolate, soft drinks, alcohol, ice cream, and candy bars (Bauer, 2).

Treatments for anemia

There are many different treatments for anemia, including monitoring food intake and iron supplementation. In severe cases of anemia, a blood transfusion may be necessary.


  • Breymann, Christian. Iron Deficiency and Anemia in Pregnancy: Modern Aspects of Diagnosis and Therapy. Blood Cells, Molecules, and Diseases. Nov/Dec: 2002.
  • Conrad, Marcel E. Iron Deficiency Anemia. EMedicine. 8 Dec. 2004.
  • Raymond, Tina. Anemia: Diagnosis, Treatment and Prevention. Midwifery Today. 31 May 1999.

Related topics

Health science - Medicine - Hematology
Hematological malignancy and White blood cells
Leukemia (ALL, AML, CLL, CML) - Lymphoma (Hodgkin's disease, NHL) - Multiple myeloma - MDS - Myelofibrosis - Myeloproliferative disease (Essential thrombocytosis, Polycythemia) - Neutropenia
Red blood cells
Anemia - Hemochromatosis - Sickle-cell anemia - Thalassemia - G6PD - other hemoglobinopathies
Coagulation and Platelets
Thrombosis - Deep venous thrombosis - Pulmonary embolism - Hemophilia - ITP - TTP

de:Anmie fr:Anmie ko:빈혈 ia:Anemia he:אנמיה lt:Anemija ms:Penyakit Anaemia nl:Bloedarmoede ja:貧血 pl:Niedokrwistość pt:Anemia fi:Anemia sv:Anemi


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