Causes
Typical causes of microcytic anemia include:

Childhood
Iron deficiency anemia by far the most common cause of anemia in general and of microcytic anemia in particular
Thalassemia
Adulthood
Iron deficiency anemia
Thalassemia
Anemia of chronic diseaseRare hereditary causes of microcytic anemia include sideroblastic anemia and other X-linked anemias, hereditary hypotransferrinemia, hereditary aceruloplasminemia, erythropoietic protoporphyria, iron-refractory iron deficiency anemia, and other thalassemic mutations (such as hemoglobin E and hemoglobin Lepore syndrome).Rare acquired causes of microcytic anemia include lead poisoning, zinc deficiency, copper deficiency, alcohol, and certain medications.Other causes that are typically thought of as causing normocytic anemia or macrocytic anemia must also be considered, as the presence of two or more causes of anemia can distort the typical picture. Iron Deficiency Anemia
Nearly half of all anemia cases are due to iron deficiency as it is the most common nutritional disorder. Although it is a common nutritional disorder, most causes of iron deficiency anemia (IDA) are due to blood loss. It is also more common to occur among children and females who are menstruating but can occur to any individual of any age. As well as a low MCV, diagnostic criteria includes low serum ferritin levels and transferrin saturation may also be used. Non-pharmacological measures to treat IDA include increasing sources of dietary iron, especially from heme sources such are liver, seafood, and red meats. However, these measures often take a great deal of time longer to replete iron stores compared to pharmacological agents such as iron supplements which are the mainstay of treatment.
Pharmacological agents may also be required in cases where deficiency is more severe, in cases where iron loss exceeds dietary intake, and in individuals who follow a plant-based diet as non-heme sources often have lower bioavailability. When oral iron supplements are used, they should be taken on an empty stomach to increase absorption This might increase the risk of side effects however, such as nausea and epigastric pain. Anemia of Chronic Disease
Anemia of chronic disease (ACD) is the second most common cause of anemia after IDA. It usually occurs in individuals that have chronic inflammation due to a medical condition. Both diagnosis and treatment can be difficult as there may be an overlap with iron deficiency and thus it is a diagnosis of exclusion. Since ACD is caused by an underlying disorder, complete resolution of the condition is unlikely and we focus on controlling the inflammatory disorder rather than treating the ACD itself. Potential inflammatory conditions that can cause ACD are pulmonary tuberculosis, rheumatoid arthritis, and malignancies among many others. Thalassemia
Thalassemia is an inherited condition that has variants in alpha or beta globin genes that result in lower levels of globin chains required to make hemoglobin, resulting in alpha thalassemia or beta thalassemia, respectively. Diagnosis is made by DNA analysis for alpha thalassemia and hemoglobin analysis for beta thalassemia. Management of thalassemia involves chronic transfusions that maintain a hemoglobin level that reduces symptoms of anemia as well as suppresses extramedullary hematopoiesis which can lead to multiple morbidities.