The hematocrit is usually done on a person with symptoms of anemia. An anemic person has fewer or smaller than normal red cells. A low hematocrit , combined with other abnormal blood tests, confirms the diagnosis. Hematocrit is the percentage of red blood cells in the blood. Learn about the normal ranges by age, the symptoms and causes of low or high hematocrit , and how to treat it. A hematocrit test is a simple blood test that measures the percentage of red blood cells in your blood . Red blood cells are important because they carry oxygen throughout your body. Women typically have lower hematocrit levels than men. This happens because women lose blood during menstrual periods. Hematocrit levels work together with other blood test results. Doctors also look at hemoglobin levels and mean corpuscular volume (MCV) to get a complete picture. MCV measures the average size of red blood cells. This helps doctors figure out what might be causing abnormal hematocrit levels. Understanding High Hematocrit Levels High hematocrit levels indicate an elevated ...