The hematocrit is a test which measures the percentage of blood that is made up of red blood cells. This test is often used to screen for anemia, or alternatively is measured on a person to determine the extent of anemia in a person. An anemic person has lesser or smaller than normal red blood cells. A low hematocrit, combined with other abnormal blood tests usually confirms the diagnosis. The hematocrit is decreased in a variety of common conditions including chronic and recent acute blood loss, some cancers, and kidney and liver diseases. Red blood cells, white blood cells (WBCs), platelets, and plasma constitute blood. A decrease in the number or size of red blood cells also decreases the amount of space they occupy, resulting in a lower hematocrit. On the contrary, an increase in the number or size of red cells increases the amount of space they occupy, resulting in a higher hematocrit.
Hematocrit is usually measured by manual centrifugation of a small capillary called microhematocrit. Due to centrifugal action various constituents of blood result in the formation of various separate layers. The height of the red column of red cells is measured as a percent of the total blood column. The height of the column of red cells is directly proportional to the hematocrit count. Automated blood cell counter can also be used to measure hematocrit.
In certain cases like dengue fever, a high hematocrit increases risk. Along with this, an increased hematocrit may cause Erythremia, a condition in which the bone marrow makes too many red blood cells. Many other conditions like chronic obstructive pulmonary disorder (COPD) in which the air ways in the lungs become narrow causing acute shortness of breath. This also increases production of red blood cells. This particular increase can be moderated by increasing levels of erythropoietin, which a glycoprotein hormone that controls red blood cell production.
The levels of hematocrit in professional sportsmen and athletes are measured as a part of the doping test. This is done because the increased hematocrit level may cause an increase risk of getting a stroke or attack due to the formation of blood clots. The use of steroids also increases the amount of red blood cells, thereby increasing the hematocrit impact. In cases where the test is carried on patients who have had excessive loss of water from the body, dehydration in other words the level of hematocrit may appear to be elevated. Tests should be carried out again after the patient is sufficiently hydrated.