Red blood cell (RBC) indices provide information about the mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and RBC distribution width (RDWCV and RDWSD). The hematocrit, RBC count, and total hemoglobin tests are used to determine the RBC indices. MCV is determined by dividing the hematocrit by the total RBC count and is helpful in classifying anemias. MCH is determined by dividing the total hemoglobin concentration by the RBC count. MCHC is determined by dividing total hemoglobin by hematocrit. Hemoglobin content is indicated as normochromic, hypochromic, and hyperchromic. The RDW is a measurement of cell size distribution over the entire RBC population measured. It can indicate anisocytosis, or excessive variations in cell size. Cell size is indicated as normocytic, microcytic, and macrocytic. RDWCV is an indication of variation in cell size over the circulating RBC population. The RDWSD is also an indicator of RBC size, is not affected by the MCV as with the RDWCV index, and is a more accurate measurement of the degree of variation in cell size. (See monographs titled “Complete Blood Count, Hemoglobin,” “Complete Blood Count, Hematocrit,” “Complete Blood Count, RBC Count,” and “Complete Blood Count, RBC Morphology and Inclusions.”)