A hematocrit blood test or an HCT blood test is a test where the total volume of red blood cells is checked vis-a-vis the volume of blood that has been drawn. The HCT blood test is therefore used to determine how much of the blood drawn is made up of red blood cells. There are two factors that are variables when it comes to the HCT blood test results. The number of red blood cells in the blood is one such factor. The other factor is the size of each red blood cell. Also read more ...