Microcytic anaemia is any of several types of anaemia characterized by small red blood cells (called microcytes). The normal mean corpuscular volume (abbreviated to MCV on full blood count results, and also known as mean cell volume) is approximately 80–100 fL. When the MCV is <80 fL, the red cells are described as microcytic and when >100 fL, macrocytic (the latter occurs in macrocytic anemia). The MCV is the average red blood cell size. In microcytic anaemia, the red blood cells (erythrocytes) contain less hemoglobin and are usually also hypochromic, meaning that the red blood cells appear paler than usual. This can be reflected by a low mean corpuscular hemoglobin concentration (MCHC), a measure representing the amount of hemoglobin per unit volume of fluid inside the cell; normally about 320–360 g/L or 32–36 g/dL. Typically, therefore, anemia of this category is described as "microcytic, hypochromic anaemia".
Folic acid supplements are also recommended for some cases of thalassemia. Evaluation and Diagnosis
In theory, the three most common microcytic anemias (iron deficiency anemia, anemia of chronic disease, and thalassemia) can be differentiated by their red blood cell (RBC) morphologies. Anemia of chronic disease shows unremarkable RBCs, iron deficiency shows anisocytosis, anisochromia and elliptocytosis, and thalassemias demonstrate target cells and coarse basophilic stippling. In practice, though elliptocytes and anisocytosis are often seen in thalassemia and target cells occasionally in iron deficiency. All three may show unremarkable RBC morphology. Basophilic stippling is one morphologic finding of thalassemia which does not appear in iron deficiency or anemia of chronic disease. The patient should be in an ethnically at-risk group and the diagnosis is not confirmed without a confirmatory method such as hemoglobin HPLC, H body staining, molecular testing or another reliable method. Coarse basophilic stippling occurs in other cases as seen in Table 1.As IDA and ACD can often be confused, it is important to evaluate their laboratory parameters. IDA is associated with low hemoglobin, ferritin, transferrin saturation, and MCV. It is also associated with a normal C-reactive protein and high transferrin. ACD is associated as well with low hemoglobin but ferritin may be normal-high, and transferrin saturation, transferrin, and MCV may be low-normal. An additional difference between IDA and ACD is that ACD is often associated with high C-reactive protein. See also
Hypochromic anemia

References
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Emedicine on chronic anemia