Anemia or anemia 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.
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 by 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. 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.
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.
The most common type of
anemia overall is iron deficiency anemia, which is most often microcytic.
Much rarer causes are hemoglobinopathies such as sickle cell anemia and
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 cells. In the United States, 20% of
all women of childbearing age have iron deficiency anemia, compared with
only 2% of adult men. In older patients, iron deficiency anemia of often
due to bleeding lesions of the gastrointestinal tract
Normocytic anemia can be
caused by acute blood loss, chronic disease, or failure to produce enough
red blood cells. Certain hormonal deficiencies, like testosterone
deficiency, 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 anemia is much rarer than dietary deficiency or genetic defect
anemia and progresses rapidly.
The most common cause of
macrocytic anemia is megaloblastic anemia due to a deficiency of either
vitamin B12 or folic acid (or both) due either to inadequate intake or
insufficient absorption. Folate deficiency normally does not produce
neurological symptoms, while B12 deficiency does. Pernicious anemia is an
autoimmune condition where the body lacks intrinsic factor, required to
absorb vitamin B12 from food. Alcoholism can cause macrocytic anemia.
William Murphy first devised
the treatment for vitamin B12-deficient macrocytic and pernicious anemias.
He bled dogs to make them anemic and then fed them various substances to
see what would make them healthy again. He discovered that ingesting large
amounts of liver seemed to cure the disease.
Fanconi anemia - a 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,
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.