ANEMIAS

GENERAL APPROACH TO ANEMIAS
Anemia is present in adults if the hematocrit is less than 41% (hemoglobin < 13.5 g/dL) in males or less than 37% (hemoglobin < 12 g/dL) in females. Congenital anemia is suggested by the patient’s personal and family history. Poor diet results in folic acid deficiency and contributes to iron deficiency, but bleeding is much more commonly the cause of iron deficiency in adults. Physical examination includes attention to signs of primary hematologic diseases (lymphadenopathy, hepatosplenomegaly, or bone tenderness). Mucosal changes such as a smooth tongue suggest megaloblastic anemia.
Anemias are classified according to their pathophysiologic basis, ie, whether related to diminished production or accelerated loss of red blood cells (Table 13–1), or according to cell size (Table 13–2). The diagnostic possibilities in microcytic anemia are iron deficiency, thalassemia, and anemia of chronic disease. A severely microcytic anemia (mean cell volume [MCV] < 70 fL) is due either to iron deficiency or thalassemia. Macrocytic anemia may be due to megaloblastic (folate or vitamin B12 deficiency) or nonmegaloblastic causes, in particular myelodysplasia and the use of antiretroviral drugs. A severely macrocytic anemia (MCV > 125 fL) is almost always megaloblastic; exceptions are the myelodysplastic syndromes.
See Related Guideline from CURRENT Practice Guidelines in Primary Care 2007

Table 13–1. Classification of anemias by pathophysiology.

Decreased production
Hemoglobin synthesis: iron deficiency, thalassemia, anemia of chronic disease
DNA synthesis: megaloblastic anemia
Stem cell: aplastic anemia, myeloproliferative leukemia
Bone marrow infiltration: carcinoma, lymphoma
Pure red cell aplasia
Increased destruction
Blood loss
Hemolysis (intrinsic)
Membrane: hereditary spherocytosis, elliptocytosis
Hemoglobin: sickle cell, unstable hemoglobin
Glycolysis: pyruvate kinase deficiency, etc
Oxidation: glucose-6-phosphate dehydrogenase deficiency
Hemolysis (extrinsic)
Immune: warm antibody, cold antibody
Microangiopathic: thrombotic thrombocytopenic purpura, hemolytic-uremic syndrome, mechanical cardiac valve, paravalvular leak
Infection: clostridial
Hypersplenism

Table 13–2. Classification of anemias by mean cell volume.

Microcytic
Iron deficiency
Thalassemia
Anemia of chronic disease
Macrocytic
Megaloblastic
Vitamin B12 deficiency

Folate deficiency
Nonmegaloblastic
Myelodysplasia, chemotherapy
Liver disease
Increased reticulocytosis
Myxedema
Normocytic
Many causes