Anemia is a condition in which the number of red blood cells or the level of hemoglobin is low.
Red blood cells contain hemoglobin, a protein that enables them to carry oxygen from the lungs and deliver it to all parts of the body. When the number of red blood cells or the hemoglobin level is reduced, the blood cannot carry an adequate supply of oxygen. An inadequate supply of oxygen in the tissues causes the symptoms of anemia.
Causes of Anemia
The causes of anemia are numerous, but most can be grouped within 3 major mechanisms that produce anemia:
Blood loss (excessive bleeding)
Inadequate production of red blood cells
Excessive destruction of red blood cells
Common Causes of Anemia
Mechanism | Examples |
|---|---|
Chronic excessive bleeding | Cancer in the digestive tract Ulcers in the stomach or small intestine |
Sudden excessive bleeding | Injuries A ruptured blood vessel Surgery |
Decreased red blood cell production | Alcohol use disorder Aplastic anemia/ pure red blood cell aplasia Chronic inflammation, infection, or cancer (anemia of chronic disease) Metastatic cancer to bone marrow Myelodysplasia (abnormalities in bone marrow tissue) Myelofibrosis (scarring of the bone marrow) |
Increased red blood cell destruction | Autoimmune reactions against red blood cells Glucose-6-phosphate dehydrogenase (G6PD) deficiency Hereditary elliptocytosis Hereditary spherocytosis Hereditary stomatocytosis Hereditary xerocytosis Mechanical damage to red blood cells (eg, heart valve-associated hemolysis (destruction of red blood cells), thrombotic microangiopathy (destruction of red blood cells, low platelets, and organ injury due to the formation of clots in the small blood vessels) Paroxysmal nocturnal hemoglobinuria Sickle cell disease (hemoglobin SS disease, hemoglobin S-C disease, hemoglobin S-Beta thalassemia) Thalassemia (both decreased red cell production due to destruction of red cell precursors in bone marrow and increased red blood cell destruction in circulation) |
More About Some Causes of Anemia
Cause | Mechanism | Treatment | Comments |
|---|---|---|---|
An enlarged spleen traps and destroys red blood cells. | The disorder that caused the spleen to enlarge is treated. Sometimes the spleen must be removed surgically. | Extremely large spleens cause abdominal pain and a feeling of fullness after eating a small amount of food. Often, an enlarged spleen also traps platelets and white blood cells, thus reducing their number in the bloodstream. | |
Mechanical damage to red blood cells | Abnormalities in blood vessels or an artificial or damaged heart valve can break normal red blood cells apart. | The cause of the damage is identified and corrected. | Red blood cells are destroyed in the blood vessels. |
The immune system destroys red blood cells. Hemoglobin from these destroyed cells is concentrated in urine, resulting in dark, reddish urine. | Medications that block the complement system, help relieve symptoms and reduce the risk of blood clots. | People may have severe stomach cramps and clotting in the large veins of the abdomen, brain, and legs. Symptoms often occur in episodes (paroxysmally), though there is also chronic destruction of red blood cells | |
Hereditary spherocytosis | Red blood cells become misshapen and rigid, getting trapped and destroyed in the spleen. | Treatment is usually not needed, but severe anemia may require removal of the spleen. | This hereditary disorder can also cause bone abnormalities and growth delays in severe cases This disorder can cause gallstones. Transient aplastic crises can occur (when the bone marrow cannot produce enough red blood cells to compensate for the chronic red cell destruction) due to infections, such as parvovirus B19, |
Hereditary elliptocytosis | Red blood cells are oval or elliptical in shape rather than the normal disk shape. | Severe anemia may require removal of the spleen. | The anemia is usually mild and requires no treatment. |
Red blood cell enzyme abnormalities | Glucose-6-phosphate dehydrogenase (G6PD) deficiency: The G6PD enzyme is missing from red blood cells , making cells more susceptible to destruction. Pyruvate kinase (PK) deficiency, which is usually present at birth (congenital), also makes red blood cells more fragile. | In G6PD deficiency, anemia can be prevented by avoiding things that trigger it, such as medications. In PK deficiency, some people may benefit from removal of the spleen and medications for anemia. | G6PD deficiency is a hereditary disorder that almost always affects males. About 10% of males with African or Black American ancestry and a smaller percentage of people of Mediterranean ancestry have G6PD deficiency. Pyruvate kinase deficiency is rare. |
Other red blood cell membrane abnormalities | Stomatocytosis (where the cell membrane has an abnormal "slit"), which can be inherited or can develop during life (acquired), or in rare cases of low phosphate levels in the blood. | For acquired stomatocytosis, people should avoid triggers (such as alcohol). For inherited stomatocytosis, rarely removal of the spleen is needed. For people with low phosphorus levels in the blood, phosphate supplements are needed. | The anemia is usually mild and requires no treatment. |
Anemia caused by excessive bleeding
Anemia may be caused by excessive bleeding. Bleeding may be sudden, as may occur as a result of an injury or during surgery. Often, bleeding is gradual and repetitive (chronic bleeding), typically due to abnormalities in the digestive or urinary tract or heavy menstrual periods. Chronic bleeding typically leads to low levels of iron, which leads to worsening anemia (see Iron Deficiency Anemia). Bleeding from the gastrointestinal tract may be slow and gradual (eg. polyps or cancers) or sudden and massive (eg, ruptured artery in an ulcer or diverticulum or ruptured esophageal varices).
Anemia due to inadequate red blood cell production
Anemia may also result when the body does not produce enough red blood cells (see also Formation of Blood Cells). Many nutrients are needed for red blood cell production. The most critical are iron, vitamin B12, and folate (folic acid), but the body also needs trace amounts of copper, as well as a proper balance of hormones, especially erythropoietin (a hormone that stimulates red blood cell production). Without these nutrients and hormones, production of red blood cells is slow and inadequate, or the red blood cells may be deformed and unable to carry oxygen adequately.
Chronic inflammation, infection, or cancer also may suppress red blood cell production. In other circumstances, the bone marrow space may be invaded and replaced (for example, by leukemia, lymphoma, or metastatic cancer), resulting in decreased production of red blood cells.
Anemia due to excessive red blood cell destruction
Anemia may also result when too many red blood cells are destroyed. Normally, red blood cells live about 120 days. Scavenger cells in the bone marrow, spleen, and liver detect and destroy red blood cells that are near or beyond their usual life span. If red blood cells are destroyed prematurely (hemolysis), the bone marrow tries to compensate by producing new cells faster. When destruction of red blood cells exceeds their production, anemia results. Hemolytic anemia is relatively uncommon compared with the anemia caused by excessive bleeding and decreased red blood cell production. Hemolytic anemia may result from disorders of the red blood cells themselves, but often it results from other disorders that cause red blood cells to be destroyed.
Symptoms of Anemia
Symptoms vary depending on the severity of the anemia and how rapidly it develops. Some people with mild anemia, particularly when it develops slowly, have no symptoms at all. Other people may experience symptoms only during physical exertion. More severe anemia may cause symptoms even when people are resting. Symptoms are more severe when mild or severe anemia develops rapidly, such as when bleeding occurs when a blood vessel ruptures.
Mild anemia often causes fatigue, weakness, and paleness. In addition to these symptoms, more severe anemia may cause faintness, dizziness, increased thirst, sweating, a weak and rapid pulse, and rapid breathing. Severe anemia may cause painful lower leg cramps during exercise, shortness of breath, and chest pain, especially if people already have impaired blood circulation in the legs or certain types of lung or heart disease.
Some symptoms may also give clues to the cause of the anemia. For example, black tarry stools, blood in the urine or stool, or coughing up blood suggests that anemia is caused by bleeding. Dark urine or jaundice (a yellowish tinge to the skin or the whites of the eyes) suggests that red blood cell destruction may be the cause of anemia. A burning or prickling feeling in the hands or feet may indicate vitamin B12 deficiency.
Anemia in older adults
Many disorders that cause anemia, such as cancer, including blood cancers such as myelodysplastic syndrome and multiple myeloma, tend to be more common among older adults. Thus, many older adults develop anemia. Anemia of chronic disease (caused by chronic inflammation, infection, or cancer) and iron deficiency anemia caused by abnormal bleeding are the most common causes of anemia among older adults. Anemia is not a normal consequence of aging, and a cause should always be sought when anemia is identified.
Symptoms of anemia are basically the same regardless of age. Even when anemia is mild, older adults are more likely to become confused, depressed, agitated, or listless than younger people. They may also become unsteady and have difficulty walking. These problems can interfere with being able to live independently. However, some older adults with mild anemia have no symptoms at all, particularly when anemia develops gradually, as it often does.
In older adults, anemia caused by vitamin B12 deficiency may be mistaken for dementia because this type of anemia may affect mental function.
Having anemia may shorten the life expectancy of older adults. Thus, identifying the cause and correcting it are particularly important.
Diagnosis of Anemia
Blood tests
Sometimes anemia is detected before people notice symptoms when routine blood tests are done.
Low levels of hemoglobin or a low hematocrit (the percentage of red blood cells in the total blood volume) found in a blood sample confirm the anemia. Other tests, such as examining a blood sample under a microscope and, less often, examining a sample taken from the bone marrow, help determine the cause of the anemia.
Treatment of Anemia
Treatment for the cause of anemia
Blood transfusion if needed
Treatment of anemia depends on identifying the cause.
For people with excessive bleeding, stopping the bleeding is most urgent. For example, if a wound has significant bleeding, pressure can stop the bleeding, but surgery may be needed. Bleeding in the gastrointestinal tract, such as from an ulcer, can often be stopped by endoscopy or other measures. Chronic uterine bleeding may require, for example, oral contraceptives or removal of uterine fibroids.
Inadequate production of blood cells is often caused by an inadequate amount of a vitamin or nutrient required to make blood, such as iron or B12.
People whose red blood cells are destroyed prematurely (hemolysis) may require treatment with medications that suppress the immune system.
Ultimately, if the anemia is severe or causes symptoms, blood transfusions may be needed and can be life-saving.
