Diagnosis of anemia. Clues to greater precision.

Typical features on the blood smear suggest the diagnosis in some types of anemia, such as the common microcytic anemias, megaloblastic anemias, and certain hemolytic anemias. Some laboratory tests used in anemia, particularly measurement of serum vitamin B12 and folate levels, may present problems in interpretation, which must be recognized if diagnostic errors are to be avoided. Normocytic anemias that are nonhemolytic, have no obvious cause, and are characterized by marked red cell changes on the blood smear should prompt careful investigation for malignancy or marrow fibrosis. Anemias are often multifactorial, and the diagnosis must be reevaluated after the apparent contributing causes have been treated. A number of "danger signs" in a patient with anemia point to the need for hematologic consultation.