What is anemia?
Anemia is a condition that occurs when the number of red blood cells (RBCs) and/or the amount of hemoglobin found in the red blood cells drops below normal. Red blood cells and the hemoglobin contained within them are necessary for the transport and delivery of oxygen from the lungs to the rest of the body. Without a sufficient supply of oxygen, many tissues and organs throughout the body can be adversely affected. Anemia can be mild, moderate or severe depending on the extent to which the RBC count and/or hemoglobin levels are decreased. It is a fairly common condition, affecting both men and women of all ages, races, and ethnic groups. However, certain people are at an increased risk of developing anemia. These include people with diets poor in iron and vitamins, chronic diseases such as kidney disease, diabetes, cancer, inflammatory bowel disease, a family history of inherited anemia, chronic infections such as tuberculosis or HIV, and those who have had significant blood loss from injury or surgery.
In general, anemia has two main causes:
- Impaired or decreased production of RBCs as, for example, in iron deficiency, B vitamin deficiencies, and aplastic anemia
- Decreased survival, increased destruction of red blood cells as in hemolytic anemia
There are several different types of anemia and various causes. Some of the most common types are summarized in the table below. Click on the links to read more about each one.
|Type of Anemia||Description||Examples of Causes|
|Iron Deficiency||Lack of iron leads to decreased amounts hemoglobin; low levels of hemoglobin in turn leads to decreased production of normal RBCs||Blood loss; diet low in iron; poor absorption of iron|
|Pernicious Anemia and B Vitamin Deficiency||Lack of B vitamins does not allow RBCs to grow and then divide as they normally would during development; leads to decreased production of normal RBCs||Lack of intrinsic factor; diet low in B vitamins; decreased absorption of B vitamins|
|Aplastic||Decreased production of all cells produced by the bone marrow of which RBCs are one type||Cancer therapy, exposure to toxins, autoimmune disorders, viral infections|
|Hemolytic||RBCs survive less than the normal 120 days in the circulation; leads to overall decreased numbers of RBCs||Inherited causes include sickle cell and thalassemia; other causes include transfusion reaction, autoimmune disease, certain drugs (penicillin)|
|Anemia of Chronic Diseases||Various conditions over the long term can cause decreased production of RBCs||Kidney disease, diabetes, tuberculosis or HIV|
Anemia may be acute or chronic. Chronic anemia may develop slowly over a period of time with long-term illnesses such as diabetes, chronic kidney disease, or cancer. In these situations, the anemia may not be apparent because symptoms are masked by the underlying disease. The presence of anemia in chronic conditions may often go undetected for a period of time and sometimes may only be discovered during tests or examinations for other conditions.
Anemia may also occur in acute episodes such as with certain hemolytic anemias in which a significant number of RBCs are destroyed. Signs and symptoms may become apparent very quickly and the cause determined from a combination of physical examination, medical history, and testing.
Signs and Symptoms
Though different types of anemias have different causes, the signs and symptoms can be very similar. Mild or moderate forms of anemia may cause few, if any, symptoms. The most common symptoms are:
- General feeling of tiredness or weakness (fatigue)
- Lack of energy
Other signs and symptoms that may develop as the anemia becomes more severe include headache, dizziness, feeling of cold or numbness in hands and/or feet, pale complexion, shortness of breath, fast or irregular heartbeat, and chest pain.
Complete Blood Count (CBC)
Anemia may first be detected when a complete blood count (CBC) is done during a health exam or as part of testing for other conditions. A CBC is often ordered as part of a yearly physical exam. It is a routine test that counts the number and relative proportion of each of the different types of cells in your blood stream. It gives your doctor information about the size, shape, and relative maturity of the blood cells present in your blood at that moment.
Blood Smear and Differential
If results of the CBC indicate anemia, it may be followed up with an examination of a Blood Smear or a Differential. Results from these tests may give clues as to the cause. Several other tests may be run to help determine the cause of the anemia and to guide treatment. See the individual discussions of the different types of anemia for more on these.