The hematocrit or packed cell volume (PCV) is a part of the complete blood count (CBC) and denotes the percent of whole blood that is composed of red blood cells. It is a measure of both the number of RBCs and the size of red blood cells (RBCs). The blood is centrifuged and the cells settle to the bottom of the tube.
The cellular portion (almost exclusively comprising RBCs) is compared with the total amount of blood and expressed as a percent. It is usually 3 times the value of hemoglobin. Conditions of low oxygen tension like high altitude, heavy smoking etc. increase the hematocrit. A reduced value denotes anemia (of any cause) while a high hematocrit may indicate dehydration (e.g. burns, vomiting, diarrhoea), increased red cell production (erythrocytosis due to any cause) or malignant proliferation of red cells (polycythemia vera). The value in males ranges from 40.7-50.3% and in females: 36.1-44.3% though these reference values are dependent on many factors like patient age, gender, sample population, and test method.