The Blood Test to Determine HCT Level: Its Purpose in Laboratory Science
written by: Loretta Snyder•edited by: Emma Lloyd•updated: 8/27/2010
An HCT blood test is performed as part of a CBC, or complete blood count. Learn why the doctor orders this test and how the results help in diagnosing medical conditions.
slide 1 of 6
The HCT, which stands for hematocrit, blood test measures the amount of red blood cells in a blood sample. This test is also referred to as a crit or a PCV, which means packed cell volume.
The HCT blood test is usually done as part of a CBC, or complete blood count, blood test. The doctor may order a CBC as part of routine blood work during a physical exam or if the patient shows signs of anemia, leukemia or other medical conditions.
slide 2 of 6
The blood sample for a hematocrit blood test is drawn from a vein, usually in the arm, and collected into a vacuum tube.
An alternative method of collection is a finger-stick, or heel-stick in newborns. This method requires that less blood and the sample is collected in a tiny tube called a pipette.
slide 3 of 6
Hematocrit values are measured in percentages. The value measures what percentage of red blood cells a blood sample contains. For example, a hematocrit 47% means that for every 100 mL of blood, 47 mL are red blood cells.
The normal range for a male is between 40.7% and 50.3%. The normal range for a female is between 36.1% and 44.3%.
slide 4 of 6
Low HCT Results
Low HCT results occur when the body's volume of red blood cells decrease, either by producing less or destroying more red blood cells. A low hematcrit result may indicate anemia, malnutrition, nutritional deficiencies, bleeding or overhydration.
Anemia is the most common cause of a low hematocrit result. Anemia occurs when the body has a below normal amount of red blood cells. This causes a hematocrit levels fall below normal.
Malnutrition or nutritional deficiencies of certain vitamins or minerals can lead to anemia and produce low HCT blood test results.
Pregnant women may have a slightly lower HCT result because of extra fluid in the body. Women of childbearing age may experience temporary decreases in HCT levels due to menstruation or iron deficiencies.
slide 5 of 6
High HCT Results
High hematocrit results occur when there is a reduction in plasma volume or an increase in red blood cells. Possible causes include dehydration, low blood oxygen levels, erythrocytosis, polycythemia vera and congenital heart disease.
The most the most common condition that causes high HCT levels is dehydration. Dehydration occurs when the body does not have as much fluid as needed and can be cause to by not drinking enough, vomiting or diarrhea.
Polycythemia vera, also known as erythrocytosis, is an abnormal increase in the red blood cells that are produced in the bone marrow.
Low blood oxygen levels, which may be present in a variety of pulmonary diseases, as well as and congenital heart disease, may result in a reduction in plasma volume and elevated hematocrit results.