Definition 

Generally, a hemoglobin (Hb) or hematocrit (Hct) less than two standard deviations below the mean, roughly equivalent to a Hb <13.5 g/dL or a Hct <41% in men, and a Hb <12.0 or a Hct <36% in women. 

Differential Diagnosis

Created by categorizing the anemia by reticulocyte count (underproduction vs. increased destruction), MCV (microcytic, normocytic, macrocytic) and cell morphology on peripheral blood smear.

Evaluation 

• Signs include pallor (including conjunctival), tachycardia, and in cases of hemolysis, jaundice; symptoms include fatigue, dyspnea on exertion, and occasionally angina from demand ischemia. Subacute and chronic anemia are often less symptomatic.
• Check a reticulocyte count: reported as either an absolute or relative (percent) reticulocyte count. If your lab provides a percent reticulocyte count, it needs to be converted to an absolute count. Both need to be corrected for early reticulocyte release to yield a Reticulocyte Index (RI).
  • Absolute reticulocyte count = % reticulocytes x (actual hematocrit ÷ ideal hematocrit). 
  • Correct for early release of reticulocytes by dividing by (1 + 0.5x) where x is 1 for every drop of 10% in the hematocrit. For example, divide by 1.5 for HCT=35% and divide by 2 for HCT=25%.
  • If the RI <2 for HCT 10-35%, or <3 for HCT <10%, a hypoproliferative anemia is present.
• Whenever a CBC is abnormal and the etiology is unclear, a peripheral blood smear should be examined manually. It is important to remember that automated cell counters frequently both under- and over-estimate various RBC indices. See section Blood Smear Basics for some common findings.
• Additional work-up and management is guided by the sub-category of anemia.