microcytic

Microcytic describes red blood cells that are smaller than normal, typically reflected by a mean corpuscular volume (MCV) below 80 femtoliters in adults. The term is used in the evaluation of anemia and is often accompanied by hypochromia, or reduced hemoglobin content per cell.

The most common cause is iron deficiency anemia, followed by inherited conditions such as thalassemias, and by sideroblastic anemia and anemia of inflammation or chronic disease. Less common causes include lead exposure, copper deficiency, and various rare genetic disorders affecting heme or globin synthesis.

Laboratory evaluation shows reduced MCV and often reduced mean corpuscular hemoglobin (MCH). Red cell distribution width (RDW) may be elevated in iron deficiency but is often normal in thalassemia trait. Peripheral smear features include microcytosis with hypochromia; target cells can be present in thalassemias and other disorders. Iron studies assist in distinguishing causes: low ferritin with low transferrin saturation suggests iron deficiency; normal or high ferritin with low transferrin saturation suggests anemia of inflammation; hemoglobin electrophoresis can identify thalassemias. Additional tests, such as lead level, may be warranted if exposure is suspected.

Management targets the underlying cause. Iron deficiency is treated with oral or IV iron and dietary adjustments. Thalassemias are monitored and managed with avoidance of unnecessary iron; transfusions or other therapies may be needed for more severe disease. Sideroblastic anemia may respond to pyridoxine (vitamin B6) in some cases and requires specific treatment for lead poisoning when relevant. Persistent microcytosis warrants further hematology evaluation.