RBC mean hemoglobin concentration is the sum of hemoglobin contained in all red blood cells per liter of blood, and the normal range is 320-360 g/L. Below 320 g/L is low mean hemoglobin concentration; above 360 g/L is high mean hemoglobin concentration. Low mean hemoglobin concentration in clinical practice is commonly associated with various anemic diseases, the most common being microcytic hypochromic anemia, including both iron deficiency anemia and thalassemia. Because both types of anemia have smaller red blood cells, the amount of hemoglobin contained in red blood cells decreases, resulting in a lower mean red blood cell hemoglobin concentration. Increased mean erythrocyte hemoglobin concentration is commonly seen in increased red blood cell numbers due to various causes, such as chronic hypoxic diseases and true erythrocytosis, which cause a significant increase in mean hemoglobin concentration due to an absolute increase in the number of red blood cells.