The initial test is the determination of hemoglobin level and hematocrit. In the case of acute bleeding, hemoglobin determination should be repeated at regular intervals as hemodilution and equilibration take 24 to 48 h to be completed and will be affected by (rapid) intravenous fluid replacement. Furthermore, the expected variability in hemoglobin testing is an important factor in the interpretation of the laboratory results.
In the work-up of the patient with anemia, the readily obtainable results of red cell smear and red cell indices will aid classification of the anemia. When the reticulocyte count is high, red cell production is sufficient. If the reticulocyte count is low, a bone marrow examination is indicated to diagnose a primary bone marrow failure.
Particularly in cases of microcytic hypochromic anemia, regular testing for occult blood loss in the feces may be helpful in identifying the site of blood loss. However, a hypochromic anemia with a negative occult feces test and no other explanation for blood loss must lead to further examination of the gut by endoscopic or radiographic examination.
Calculation of red cell indices and the reticulocyte count are also particularly helpful in the diagnosis and classification of anemias due to underproduction of red cells. Microcytic anemia
This represents a group with decreased availability or synthesis of one of the major constituents of the hemoglobin molecule (iron, porphyrin, or globin). Anemia during chronic inflammation or in malignancy may be slightly microcytic due to a defect in the availability of iron, although these disorders are more often associated with normocytic anemia. As mentioned earlier, in the case of microcytic anemia a source of (chronic) bleeding should be regarded as the most important factor to exclude first.
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