Causes of low hematocrit levels include a red blood cell deficiency, malnutrition and nutritional deficiencies, a large number of white blood cells, and a recent or long-term blood loss, according to Mayo Clinic. Low hematocrit levels for adult men and women fall below 38.8 percent and 34.9 percent respectively.
Doctors test hematocrit levels as part of a complete blood count or CBC test, or when they suspect a patient of having fewer red blood cells than normal, states Healthline. The hematocrit or Hct test measures the proportion of red blood cells in the total blood volume using a sample of the patient's blood. There are no risks or side effects associated with the test. Doctors use the test results to diagnose a condition they suspect such as anemia or to monitor treatment of such conditions.
The Hct test is not foolproof as some conditions can lead to incorrect or false results, cautions Mayo Clinic. These conditions include pregnancy, severe dehydration, living at a high altitude, a recent blood transfusion and massive blood loss. However, doctors are aware of this and consider such conditions when testing hematocrit levels and either verify the results through other blood tests or repeat the Hct test for a more accurate result.