Microcytic anemia is characterized by small red blood cells. The normal mean corpuscular volume (abbreviated to MCV on full blood count results) is 76-100 fl, with smaller cells (<76 fl) described as microcytic and larger cells (>100 fl) as macrocytic.

In microcytic anemia, the red blood cells (erythrocytes) are usually also hypochromic, meaning that the red blood cells are paler than usual. This can be quantified as the mean corpuscular hemoglobin or mean cell hemoglobin (MCH), the amount of hemoglobin per cell; the normal value is 27-32 picograms (pg). Similar is the mean corpuscular hemoglobin concentration or mean cell hemoglobin concentration (MCHC), giving the amount of hemoglobin per volume of erythrocytes (normally about 320-360 g/l or 32-36 g/dl). Typically, therefore, anemia of this category is described as “microcytic, hypochromic anemia”.

Microcytic anaemia is classically caused by:

• iron deficiency anemia, by far the most common cause of anemia in general and of microcytic anemia in particular;
• thalassemia;
• sideroblastic anemia, congenital or acquired;
• sometimes, anemia of chronic disease, although this more typically causes normochromic, normocytic anemia;
• lead poisoning (rare).

Other causes that are “typically” thought of as causing normocytic anemia or macrocytic anemia must also be considered, and the presence of two or more causes of anemia can distort the “typical” picture of each.

To review the differential diagnosis of anemia, click here.

• Emedicine on chronic anemia
• FP Notebook
• American Family Physician
• Overview (vet)