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Introduction
The Red Cell Disorders unit is organized mechanistically or
physiologically into three major sections: 1) Increased RBC
Destruction, 2) Decreased RBC Production, and 3) Blood Loss.
The Increased RBC Destruction or Hemolytic anemia section includes
anemias secondary to membrane disorders, enzyme deficiencies,
abnormalities of hemoglobin synthesis, antibody mediated destruction,
and mechanical trauma.
The Decreased RBC Production section includes anemias secondary to
decreased hemoglobin synthesis as in the microcytic anemias of iron
deficiency and thalessemia, and the abnormalities of DNA synthesis as
in the megaloblastic anemias, abnormalities of proliferation, and
failure of differentiation.
The final section is on anemia secondary to Blood loss. Certain
proliferative disorders of red cells are considered in the unit on
proliferative disorders of white cells.
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What is anemia? First, anemia is not a specific disease.
Anemia is the finding of too few red blood cells or an
abnormally low hematocrit or too little hemoglobin. Symptoms
of anemia include fatigue, weakness, syncope, decreased
appetite and occasionally chest pain, shock or congestive
heart failure.
Physical signs of anemia are manifest by pallor of the
skin, palmar creases, nail beds, and mucous membranes
(conjunctiva). In severe anemia the heart rate may increase.
Decreased blood pressure, often orthostatic may be present.
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It is critical to determine the cause of the anemia.
Anemia may result from 1) Increased RBC
destruction, 2) Decreased RBC
production, or 3) blood loss. A careful patient history for
evidence of blood loss should include questions regarding
gastrointestinal bleeding, hematemasis (vomiting
blood), melena (black stool), or hematochezia
(red blood in feces). Hemoptysis (coughing up
blood), epistaxis (nosebleed), and hematuria
(blood in urine) must also be investigated. Menstrual
blood loss should be estimated and questions asked regarding
menorrhagia (excessive bleeding) or metrorrhagia
(irregular bleeding).
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The quaiac test for occult blood is based on detection of
endogenous peroxidase in RBCs.
Hemoglobin and myoglobin of meat and fish can give false
+ results. Vitamin C can cause a false negative result. Why?
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Other data from the medical history may help in
determining the cause of the anemia. For instance, papillar
atrophy of the tongue and angular stomatitis are common in
megaloblastic anemia secondary to Vitamin B12 deficiency.
Peripheral neuropathy and paresthesias may accompany Vitamin
B12 deficiency. History of a malignancy and the record of
treatment are important. A review of all medications is also
indicated.
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Dietary questions may be important in assessing anemias
of childhood or the elderly. Other questions regarding the
patient's age and sex; their habits regarding exercise,
alcohol and smoking should also be considered when
investigating evidence of anemia.
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A family history of anemia, early onset of cholelithiasis
(bilirubin), or jaundice might suggest a hemolytic anemia or
possibly hemoglobin synthetic disorder.
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Of course you must check the measured blood parameters.
The Hematocrit (Hct); Hemoglobin (Hgb), and Mean Corpuscular
Volume (MCV) are the most useful parameters of the Complete
Blood Count (CBC).
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Most important is examination of a Wright's stained
peripheral blood smear by the physician.
From this one can estimate the Hct; judge the size and
the degree of size variability (anisocytosis); look for
changes in RBC shape (piokilocytosis), and judge the RBC
chromicity.
Now you are ready to review the anemias in more depth,
beginning with those caused by increased RBC destruction,
then by decreased RBC production, and finally by loss of
blood.
In the next section we begin a discussion of anemias caused
by increased RBC destruction.
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Pathology
> Basic Hematology > Red Cell
Disorders > Introduction