Anemia Classification and Diagnosis

Classification Based on MCV

The American Gastroenterological Association suggests that iron deficiency anemia is the most common cause of microcytic anemia, which is characterized by a mean corpuscular volume (MCV) less than 80 fL 1, 2
Anemia of chronic disease, which includes conditions such as cancer, infection, and inflammatory diseases, can also present with microcytic anemia 1, 3
The National Comprehensive Cancer Network recommends considering lead poisoning as a rare cause of microcytic anemia 3
Hereditary microcytic anemia, including thalassemia and sideroblastic anemia, should be considered in patients with microcytic anemia 3
Normocytic anemia, characterized by an MCV between 80-100 fL, can be caused by acute hemorrhage, renal anemia, anemia of chronic disease, and bone marrow failure 3
Vitamin B12 deficiency, folate deficiency, and medication-induced anemia can cause macrocytic anemia, characterized by an MCV greater than 100 fL 3, 4

A low or normal reticulocyte count indicates decreased production of red blood cells, which can be seen in nutritional deficiencies, bone marrow failure, and chronic disease 1, 5
A high reticulocyte count indicates increased destruction or loss of red blood cells, which can be seen in hemolysis and acute blood loss 1, 3, 5

Microcytic anemia with low or normal reticulocytes can be caused by iron deficiency, anemia of chronic disease, lead poisoning, and hereditary anemias 1, 3
Microcytic anemia with high reticulocytes can be caused by hemoglobinopathies such as thalassemia 1, 3
Normocytic anemia with low or normal reticulocytes can be caused by acute hemorrhage, renal anemia, anemia of chronic disease, and bone marrow failure 3
Macrocytic anemia with low or normal reticulocytes can be caused by vitamin B12 or folate deficiency, myelodysplastic syndrome, medication effects, and hypothyroidism 3, 4

The initial diagnostic workup for anemia should include a complete blood count with MCV, reticulocyte count, serum ferritin, transferrin saturation, and C-reactive protein 1, 6, 2

Hereditary microcytic anemias, such as thalassemia and sideroblastic anemia, should be suspected when ferritin is elevated or transferrin saturation is abnormal, family history is present, or anemia is refractory to iron supplementation, according to the American Society of Hematology 7

Functional iron deficiency in chronic disease can occur with low-normal ferritin but low transferrin saturation, as noted in the Blood journal 7