Hematocrit (Hct)

Hematocrit levels that are too high or too low can be a sign of a blood disorder, dehydration, or other medical conditions that affect your blood.

Your health care provider may order a hematocrit test as part of your routine checkup or to monitor your health if you are being treated for cancer or have an ongoing health condition. Your provider may also order this test if you have symptoms of a red blood cell disorder, such as anemia or polycythemia.

Your hematocrit test results are reported as a number. That number is the percentage of your blood that's made up of red blood cells. For example, if your hematocrit test result is 42, it means that 42% of your blood is red blood cells, and the rest is made up of white blood cells, platelets, and blood plasma.

Normal hematocrit levels will vary, depending on your sex, age, whether or not you smoke, and the altitude where you live. Ask your provider what your hematocrit level should be, and what a higher- or lower-than-normal result might mean for you.

A low hematocrit may point to anemia, recent blood loss, certain bone marrow problems, kidney disease, or fluid overload. A high hematocrit can be seen with dehydration, smoking, lung or heart disease, living at high altitude, or polycythemia. Your provider will look at your hematocrit together with the rest of your blood count and your symptoms to figure out what's going on.