MCV (mean cell volume) is the average volume of an erythrocyte, which is assessed when investigating blood cells. When haemoglobin concentration is decreased, it is necessary to look into erythrocyte indexes. The most accurate, sensitive and specific erythrocyte index is MCV. MCV can be increased even if haemoglobin has not decreased. This is a sign of pathology, for example, it happens in liver diseases. The biggest benefit of the index is that it serves for preliminary differential diagnosis of anaemia. This parameter is measured in femtolitres (fl, or 10-15L) and its normal value range for adults is 82.00-98.00 fl.