Anemia

Anemia
General Concepts-Anemia

A. Definitions
- anemia is a decrease in whole body red cell mass, a definition that precludes relative decreases in red blood cell count, hemoglobin, or hematocrit, which occur when the plasma volume is increased.
- anemia of pregnancy is not anemia but is a rather a manifestation of increased plasma volume.
- a practical working definition of anemia is a decrease in red blood cell count, hemoglobin, or hematocrit, commonly measured red cell parameters.

B. Causes of anemia
- anemia may be caused by two major mechanisms:

1. Decreased red cell production resulting from:
a. Hemopoietic cell damage from infection, drugs, radiation, and other similar agents
b. Deficiency of factors necessary for heme synthesis (iron) or DNA synthesis (vitamin B12 or folate)

2. Increased red cell loss due to:
a. External blood loss
b. Red cell destruction (hemolytic anemia)

Acute Post-hemorrhagic Anemia.

-within the first few hours of acute blood loss, prior to hemodilution (compensatory increase in plasma volume), there may be no decrease in the hemoglobin, hematocrit, and red cell count because of a parallel loss of both red cells and plasma. There is often a marked reactive increase in platelet count.
-significant clinical findings are related to hypovolemia.

Examples of Anemia Resulting from Decreased Red Cell Production:

=>Iron Deficiency anemia
+Mechnisms: Impaired heme synthesis
+Diagnostic Features: Hypochromia and microcytosis; decreased serum iron and increased total iron binding capacity; decreased serum ferritin
+Major Etiologic Factors: Dietary deficiency in infants and preadolescents; excess menstrual bleeding; chronic blood loss from gastrointestinal tract.
=>Pernicious anemia
+Mechnisms: Chronic gastritis leading to lack of gastric intrinsic factor and failure of vitamin B12 absorption; vitamin B12 deficiency causes delayed DNA replication.
+Diagnostic Features: Pancytopenia, oval macrocytes,and hypersegmented neutrophils; megaloblastic hyperplasia; achlorhydria; anti-intrinsic factor antibodies; absent position and vibration sensations; impaired vitamin B12 absorption corrected by intrinsic factor (abnormal Schilling test)
=>Folate deficiency
+Mechnisms: Delayed DNA replication
+Diagnostic Features: Pancytopenia, oval mcrocytes, and hypersegmented neutrophils; megaloblastic hyperplasia.
+Major Etiologic Factors: Dietary deficiency; malabsorption syndromes
=>Aplastic anemia
+Mechnisms: Mardedly diminished hematopoiesis.
+Diagnostic Features: Pancytopenia, reticulocytopenia, marked hypocellularity of bone marrow.
+Major Etiologic Factors: Toxic drugs and chemicals; often idiopathic.

=>Anemia of Chronic Disease:
+Mechnisms: Diverse mechanisms.
+Diagnostic Features: Anemia most often normochronic and normocytic or macrocytic; may be hypochronic and microcytic with decreased serum iron and decreased serum iron binding capacity.
+Major Etiologic Factors: Various chronic diseases, especially rheumatoid arthritis, renal disease, and chronic infection

=> Myelophthistic anemia
+Mechnisms: Bone marrow replacement, usually by malignant tumor.
+Diagnostic Features: Severe anemia; small numbers of nucleated red cells and immature granulocytes in peripheral blood; tumor cells in bone marrow.



Iron Deficiency Anemia


A. Causes
1. Increased iron requirement
-may occur during pregnancy; iron demands of the fetus can deplete maternal iron stores.
-may also occur in infants and preadolescent who may outgrow borderline iron stores.

2. Dietary deficiency
-is rare except in infants; because human milk is low in iron, newborn storage iron will be depleted within the first 6 months unless it is replaced by dietary supplementation. Premature infants are at special risk.
-may rarely occur in elderly persons

3. Chronic blood loss
-is the major cause of iron deficiency anemia in adults.
-is most often caused by menorrhagia or bleeding gastrointestinal lesions.

B. Clinical manifestations- iron deficiency anemia

-may include pallor, fatigue, or dyspnea on exertion
-sometimes includes angina pectoris in persons with coronary artery narrowing caused by atherosclerotic desease.
-when extreme, may be associated with glossitis, gastritis, koilonychia (spooning of the nails), or Plummer-Vinson syndrome, in which iron deficiency is associated with a partially obstructing upper esophegeal web.

C. Laboratory findings

1. Decreased hemoglobin, hematocrit, and red cell count.
2. Hypochromic microcytic erythrocytes on peripheral smear.
3. Decreased serum iron and increased total iron binding capacity (TIBC)
4. Decreased body iron stores, measured by bone marrow examination for stainable hemosiderin or by decreased serum ferritin



Megaloblastic Anemias

A. General characteristics-megaloblastic anemias

-are defined by large, abnormal-appearing erythroid precursor cells (megaloblasts) in the bone marrow.
-are caused by deficiency of vitamin B12 or folate.
-are characterized by decreased DNA synthesis, with a consequent delay in DNA replication and nuclear division, and by relatively unimpeded cytoplasmic maturation.
-manifest morphologically as nuclear-cytoplasmic asychrony of large erythroid precursor cells with an open, loose-appearing chromatin pattern.
-result in anemia caused by impaired red cell production; to a lesser degree, red cell destruction occurs within the bone marrow prior to release of mature erythrocytes into the peripheral blood (ineffective erythropoiesis)

MD. Kais Haider Chowdhury