A Complete Blood Count blood test, CBC, is a series of blood tests used to assess diseases that affect the blood. When a hematocrit test is ordered, the doctor wants to look at the number of red blood cells in the blood in order to monitor the response to treatment or make a diagnosis.

The word hematocrit comes from the Greek words haima and krites and means, to separate blood. The hematocrit test measures the volume of red blood cells by separating them from white blood cells, platelets, and hemoglobin. The hematocrit is measured by multiplying the red blood cell count, RBC, by the mean cell volume, also known as the mean corpuscular volume or MCV. A normal hematocrit level is between 38.8 and 50 for men and between 34.9 and 44.5 for women.

Red blood cells are responsible for carrying oxygen throughout the body and too few or too many cells can affect the delivery of oxygen and may be a sign of disease. If the hematocrit level is too low, this may be an indication of anemia or a vitamin or mineral deficiency. Symptoms of a low hematocrit level include chest pain, dizziness, headache and shortness of breath. If the hematocrit level is too high, this may be an indication of polycythemia vera, lung disease or heart disease. Symptoms of a high hematocrit level include dizziness, headache, blurred vision and heart attack.

There are additional factors that may produce inaccurate results. They include recent blood transfusions, extreme dehydration, pregnancy and certain medications.