Other Tests in the Anemic Patient
Just as many physicians automatically treat anemia with iron, many also order iron studies even if the anemia does not appear to be compatible with iron deficiency. In this case, there was no need to measure ferritin, iron, or iron-binding capacity. Not only did the patient's disorder bear no resemblance to iron deficiency, iron and ferritin levels are usually misleadingly high in untreated megaloblastic anemia. Even if the patient had an underlying iron deficiency, it would not have been identified, because blood was drawn before the B12 deficiency was corrected.
LDH is useful as an initial screening test. Identification of macrocytic pancytopenia, a high bilirubin level, and an extremely elevated lactate dehydrogenase level can be regarded as megaloblastic anemia until proved otherwise. The low reticulocyte count in this case provided evidence that few new blood cells were emerging from the bone marrow. The test was not essential here; its principal utility is in patients with suspected hemolytic anemia.
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