Overview of Anemia
Anemia is a condition in which the number of red blood
cells 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 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 three major mechanisms that produce anemia:
- Blood
loss (excessive bleeding)
- Inadequate
production of red blood cells
- Excessive
destruction of red blood cells
Anemia caused by
excessive bleeding
Anemia may be caused by excessive bleeding (see Anemia due
to 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).
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 inflammatory disease 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,
hemolytic 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 more 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 myelodysplasia and multiple myeloma, tend
to be more common among older people. Thus, many older people develop
anemia. Anemia of chronic disease and iron deficiency anemia caused
by abnormal bleeding are the most common causes of anemia among older people.
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.
Also, even when anemia is mild, older people 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 people with mild anemia
have no symptoms at all, particularly when anemia develops gradually, as it
often does.
In older people, 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
people. 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