A hematocrit (Hct) test is a 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. The test is often part of a complete blood count (CBC) and is used to check your general health. Test results showing low or high hematocrit levels may be signs of blood disorders or other medical conditions. A hematocrit test is a simple blood test that can be done by obtaining blood from a vein using a needle to fill one or more sample tubes or by using a needle prick to obtain a drop of blood. No special preparation is necessary for this test, and it is a safe procedure with very few complications. Your healthcare provider is your best resource for information about your test result. Suspected anemia is the most common reason for hematocrit testing, but it may also be done before and after major surgery, during pregnancy, or to monitor treatment for cancer.