Hematocrit, or HCT, refers to the amount of red blood cells in the entire blood volume. It is measured as a percentage. It is sometimes also referred to as packed cell volume. The hematocrit is measured through a blood test. Abnormal levels can be a sign of various medical illnesses or conditions.
Often an HCT test is ordered as part of a complete blood count. It may be repeated several times to determine if certain conditions, such as anemia, are getting better. The test involves obtaining blood from a vein. A vein, often in the arm or hand, is cleaned with an antiseptic. Next, a needle is inserted into the vein, and the blood is drawn.
Although blood tests are considered routine and rarely result in complications, problems are possible. Infection can develop, especially if the site was not cleaned well before the blood was drawn. Other rare complications that can occur include excessive bleeding and a hematoma at the site.
Once the blood is taken, it is analyzed through special lab equipment to determine the hematocrit. Lab equipment varies and different techniques may be used to get a measurement. Dense blood, containing red blood cells will separate from the liquid component of the blood after being spun in a centrifuge. This helps determine the percentage of the entire volume of blood that contains red blood cells.
Normal levels will differ depending on the patient's gender and age. For instance, in newborns, normal ranges are between 55 and 68 percent. By 10 years of age, 36 to 41 percent is considered normal. The normal male adult values are 42 to 54 percent, and in adult females a normal number is 38 to 46 percent.
A low hematocrit level can indicate various conditions such as excess blood loss, or a nutritional deficiency. Bone marrow diseases, such as leukemia, can also cause a decrease in red blood cells and result in a low hematocrit.
Various conditions may also cause an increased hematocrit. Certain lung diseases, such as chronic obstructive pulmonary disease can cause an increased ratio of red blood cells. Dehydration and being at a high elevation can also often lead to an increased hematocrit.
Another reason to check the HCT may be to check for blood doping among athletes. When an athlete uses steroids, the drugs can increase the percentage of red blood cells in the body and raise the hematocrit above normal levels. A baseline HCT level is often taken on professional athletes to determine what their HCT percentage is. That level is compared to random screenings performed to check for blood doping.