Restoration of normal red cell size after treatment in megaloblastic anaemia

The return of the MCV to normal after treatment in megaloblastic anaemia follows a biphasic pattern. The initial more rapid decline in MCV is due to disappearance of pretreatment macrocytes from the circulation and the rate of fall is determined by their mean cell life. The second slower component is probably due to a mixture of pretreatment macrocytes and new macrocytes, the result of a young red cell population. The MCV often returned to normal most rapidly in the most severely megaloblastic patients due to a very short mean red cell life span. However, there was no significant correlation between either initial MCV or red cell count and the time after treatment for a return of a normal MCV.