Abstract & Overview
The term macrocytosis refers to a blood condition in which red blood cells (RBC) are larger than normal.Macrocytosis is reported in terms of mean corpuscular volume (MCV).Normal MCV values range from 80 to 100 femtoliters (fl) and vary by age and reference laboratory. 1 MCV is calculated according to the following formula: MCV (fl) = [Hematocrit (percent) x 10]/[RBC count (10 6 /µL)] Macrocytosis can be identified by reviewing peripheral blood smears and/or by automated RBC indices.The peripheral blood smear is more sensitive than RBC indices for identifying early macrocytic changes because the MCV represents the mean of the distribution curve and is insensitive to the presence of small numbers of macrocytes. 2 However, compared to the peripheral blood smear, MCV may underestimate macrocytosis in over 30% of cases.3 Although determination of the MCV by automated blood cell counter is rarely inaccurate, hyperglycemia, marked leukocytosis and cold agglutinins may result in false elevations of the MCV.[4][5][6] Moreover, partial occlusion of the instrument aperture and/or leaving the blood sample at room temperature for several hours may also result in false elevations of the MCV value. Clinical SignificanceMacrocytosis is a relatively common finding in the era of automated blood cell counters, with prevalence estimates ranging from 1.7% to 3.6%.3,7,8 Its significance tends to be underestimated by physicians, since about 60% of patients present without associated anemia, 8 unless there are other accompanying abnormalities noted.No complications arise from macrocytosis itself as an isolated finding.However, its identification can provide important information regarding the presence of an underlying disease state.Thus, in the appropriate clinical setting, MCV values above the upper limit of normal or those that differ significantly from the patient's baseline values may require further clinical and laboratory assessment to determine the underlying cause of the macrocytosis.9