Lab Test: Hematocrit Level
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- Ratio of the volume of red blood cells to volume of whole blood expressed as a percentage or as a decimal fraction (SI units).
- The Hct is a measure of the percentage of the total blood volume that is made up by the RBCs. The height of the RBC column is measured after centrifugation and is compared to the height of the column of the total whole blood. The ratio of the height of the RBC column compared with the original total blood column is multiplied by 100% and this is the Hct value. The Hct in percentage points usually is approximately three times the Hgb concentration in g/dL when RBCs are of normal size and contain normal amounts of Hgb.
- Adult females, whole blood: 36%-46% (0.36-0.46)
- Adult males, whole blood: 41%-53% (0.41-0.53)
- Fetal and cord blood:
- 18 to 20 weeks' gestation: 35.86% +/-3.29 (0.36+/0.03)
- 21 to 22 weeks' gestation: 38.53% +/-3.21 (0.39+/0.03)
- 23 to 25 weeks' gestation: 38.59% +/-2.41 (0.39+/0.02)
- 26 to 30 weeks' gestation: 41.54%+/-3/31 (0.42+/0.03)
- Pregnant female: >33%
- Child/adolescent:
- Newborn: 44%-64%
- 2-8 weeks: 39%-59%
- 2-6 months: 35%-50%
- 6 months-1 year: 29%-43%
- 1-6 years: 30%-40%
- 6-18 years: 32%-44%
- Critical Values:
- <21% or >65%
- Decisions concerning the need for blood transfusion are usually based on the Hgb or the Hct. In an otherwise healthy person, transfusion is not usually considered as long as the Hgb is above 8 g/dL or the Hct is above 24%. In younger people who can safely and significantly increase their cardiac output, a Hct of 18% may be acceptable. In an older individual with an already compromised oxygen-carrying capacity (caused by cardiopulmonary diseases), transfusion may be recommended when the Hct level is below 30%.
- Increased levels may indicate:
- Erythrocytosis, congenital heart disease, polycythemia vera, severe dehydration (e.g., severe diarrhea, burns), or severe chronic obstructive pulmonary disease (COPD).
- Decreased levels may indicate:
- Anemia, hemoglobinopathy, cirrhosis, hemolytic anemia (e.g., erythroblastosis fetalis, hemoglobinopathies, drug-induced hemolytic anemias, paroxysmal nocturnal hemoglobinuria), hemorrhage, dietary deficiency, bone marrow failure, prosthetic vales, renal disease, normal pregnancy, rheumatoid/collagen-vascular disease (e.g., rheumatoid arthritis, lupus), lymphoma, multiple myeloma, leukemia, or Hodgkin disease.
- Hemoglobin - this is a measurement of the concentration of Hgb in the blood and is closely associated with the RBC count and Hct value.
- Red blood cell count - this is a measurement of the number of RBCs per cubic millimeter of blood.
- Red blood cell indices - these provide data about the size and Hbg content of the RBC.
- Collect whole blood sample or capillary blood sample (only 0.5 mL is required with capillary samples).
- Avoid hemolysis.
- Obtain fetal blood by percutaneous umbilical blood sampling
- Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding.
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Clinical Application
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MESH Terms & Keywords
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