What is the difference between hemoglobin and hematocrit?
Hemoglobin is a protein in red blood cells and hematocrit is a measurement of the amount of red blood cells as related to total blood cell count. Both hemoglobin and hematocrit are used to diagnose anemia. Both hemoglobin and hematocrit can be measured from standard blood tests, and both values are typically reported when a doctor orders a blood count.
The hematocrit (hct) is volume percentage of red blood cells in the blood and is expressed as a percentage. For example, a hematocrit of 25% means there are 25 milliliters of red blood cells in 100 milliliters of blood.
Why do doctors measure hemoglobin?
Hemoglobin (Hb) is a protein in red blood cells that contains an iron molecule. Hemoglobin carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs. The iron in hemoglobin plays an important role in maintaining the shape of the red blood cells.
Normal hemoglobin ranges depend on age and gender, and the “normal” range may vary by the specific test used. Normal hemoglobin levels are:
- Newborns: 17 to 22 gm/dL
- One (1) week of age: 15 to 20 gm/dL
- One (1) month of age: 11 to 15 gm/dL
- Children: 11 to 13 gm/dL
- Adult males: 14 to 18 gm/dL
- Adult women: 12 to 16 gm/dL
- Men after middle age: 12.4 to 14.9 gm/dL
- Women after middle age: 11.7 to 13.8 gm/dL
Low hemoglobin levels are referred to as anemia, or low red blood cell count. Causes of anemia include blood loss, nutritional deficiency, bone marrow disorders, bone marrow suppression by chemotherapy or radiation exposure, kidney failure, and abnormal hemoglobin structure, such as sickle cell anemia. High hemoglobin levels are often seen in people who live in high altitudes and in smokers. Other causes of high hemoglobin levels include dehydration, lung disease, cancer, bone marrow disorders (polycythemia vera), and “blood doping” by athletes.
Why do doctors measure hematocrit?
As with hemoglobin, normal hematocrit ranges depend on age and gender, and the “normal” range may vary by the specific test used. Normal hematocrit levels are:
- Newborns: 55% to 68%
- One (1) week of age: 47% to 65%
- One (1) month of age: 37% to 49%
- Three (3) months of age: 30% to 36%
- One (1) year of age: 29% to 41%
- Ten (10) years of age: 36% to 40%
- Adult males: 42% to 54%
- Adult women: 38% to 46%
Just as low hemoglobin levels signify anemia, a person with a low hematocrit percentage is also anemic. High hematocrit percentages are seen in the same populations that may have high hemoglobin levels.