Investigation of nonpoikilocytic normochromic normocytic anemia.

When the mean corpuscular volume is normal in an anemic patient, examination of a blood smear becomes of paramount importance. When the RBCs are normochronic, normocytic, and nonpoikilocytic, the reticulocyte count determines the line of investigation. When the count is increased, either hemorrhage or hemolysis is present. When the count is not increased (ie, normal or low), the differential diagnosis includes anemias due to iron deficiency, chronic disease, renal disease, hemodilution, marrow infiltration, and marrow failure (aplastic anemia). Some morphologic clues to cause other than those pertaining to RBC morphology are discussed and illustrated. A working approach to the investigation of nonpoikilocytic normochromic normocytic anemia is suggested.