ANEMIA

5 ANEMIA



General Discussion


Anemia is defined as a decrease in hemoglobin or hematocrit level from an individual’s baseline value. In general, normal hemoglobin levels are 1 to 2 g/dL lower in women and African-American men than in white men.


The initial laboratory evaluation of anemia should include a complete blood count, red blood cell indices, a reticulocyte count, and peripheral blood smear. The mean corpuscular volume (MCV) is used first to classify the anemic process as microcytic, normocytic, or macrocytic.



Microcytic Anemia


The evaluation of microcytic anemia begins by ruling out iron deficiency anemia. The definitive test for iron deficiency anemia is the serum ferritin, as a low serum ferritin level is diagnostic of an iron-depleted state. Other iron studies such as serum iron, total iron-binding capacity, and transferring saturation do not accurately distinguish iron deficiency anemia from anemia of chronic disease. In equivocal cases, a finite treatment trial with iron supplementation may help distinguish the two.


Other clues may help diagnose iron deficiency anemia. Microcytic anemia associated with increased red blood cell distribution width favors a diagnosis of iron deficiency anemia over that of anemia of chronic disease. The peripheral blood smear in iron deficiency anemia usually shows anisocytosis and poikilocytosis. Iron deficiency anemia may be associated with reactive thrombocytosis. In contrast, microcytic anemia associated with increased red blood cell count is characteristic of the thalassemia trait. Polychromasia, basophilic stippling, and target cells are absent in iron deficiency anemia but are characteristic features of the peripheral blood smear in thalassemia.


If the serum ferritin level is normal, the physician should determine if the microcytic anemia is preexisting or new. If the microcytosis is preexisting, a diagnosis of thalassemia should be considered. If the microcytosis is new, the differential diagnosis includes anemia of chronic disease and hereditary or acquired sideroblastic anemia. Anemia of chronic disease is usually normocytic, but may be microcytic in some systemic diseases such as temporal arteritis, rheumatoid arthritis, polymyalgia rheumatica, diabetes mellitus, connective tissue disease, chronic infection, Hodgkin’s lymphoma, and renal cell carcinoma. The diagnosis is made on clinical grounds, and the microcytic anemia often is accompanied by systemic signs and symptoms.



Normocytic Anemia


The evaluation of normocytic anemia begins by identifying treatable causes such as nutritional anemias, anemia of renal insufficiency, bleeding, and hemolytic anemia. The initial investigation should include a fecal occult blood test and determination of serum ferritin, serum vitamin B12, and serum folate levels. The diagnosis of anemia of renal insufficiency may be made on the basis of an elevated serum creatinine. Mild to moderate anemia may be seen when the serum creatinine is 1.5–3 mg/dL, while more severe anemia is found with more advanced renal disease. Anemia of renal insufficiency is associated with an unremarkable peripheral blood smear and a normal serum erythropoietin level.


If hemolysis is suspected, this diagnosis may be supported by a low haptoglobin level and increased lactate dehydrogenase (LDH), indirect bilirubin, and reticulocyte count. These tests are not specific and do not distinguish among the various causes of hemolytic anemia. The peripheral blood smear guides the evaluation of a suspected hemolytic anemia and is outlined in further detail below.


If a normocytic anemia is not linked to bleeding, nutrition, renal insufficiency, or hemolysis, the differential diagnosis includes a primary bone marrow disorder or normocytic anemia of chronic disease. The patient’s history and peripheral blood smear may help to differentiate these two diagnoses, and hematology consultation should be considered. Other possible causes of normocytic anemia are alcohol abuse, drug effects, radiation therapy, chemical exposure, and recent trauma or surgery.



Macrocytic Anemia


The evaluation of macrocytic anemia begins by excluding alcohol or drug use associated with macrocytosis. Drugs associated with macrocytosis include hydroxyurea, methotrexate, trimethoprim, zidovudine, and 5-fluorouracil.


Vitamin B12 and folate deficiencies must be ruled out. In vitamin B12 deficiency, the serum vitamin B12 levels are usually low, but may be falsely low in elderly patients, in patients with low white blood cell counts, and in pregnant patients. The serum methylmalonic acid level is a more sensitive and highly specific test. A normal level makes the diagnosis of vitamin B12 deficiency very unlikely. In folate deficiency, serum folate levels are usually low, but may be affected by recent dietary changes. The serum homocysteine level is increased during folate deficiency and may be used instead to evaluate for folate deficiency.


If vitamin B12 deficiency is confirmed, intrinsic factor antibodies should be ordered. If they are present, a working diagnosis of pernicious anemia is made. If intrinsic factor antibodies are not present, the Schilling test can help differentiate pernicious anemia from primary intestinal malabsorptive disorders.


If vitamin deficiency, alcohol abuse, or drug exposure cannot be implicated as the cause of a macrocytic anemia, the process should be classified into mild (MCV 100–100 fL) or marked (MCV >110 fL) macrocytosis. Marked macrocytosis that is not due to nutritional deficiency, alcohol, or drug abuse usually is associated with a primary bone marrow disease such as myelodysplastic syndrome, aplastic anemia, or pure red cell aplasia. A bone marrow biopsy should be considered if the hematologic diagnosis affects management decisions. For a mild macrocytosis, the peripheral blood smear should be examined for evidence of an association with diseases such as liver disease or hypothyroidism. Bone marrow biopsy may be necessary to clarify the diagnosis.

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Aug 17, 2016 | Posted by in PEDIATRICS | Comments Off on ANEMIA

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