Hematocrit is a measure of the proportion of red blood cells (RBCs) in your blood. It is expressed as a percentage and represents the volume of red blood cells compared to the total blood volume, which includes plasma (the liquid part of blood) and other cells.
For example:
- A hematocrit of 40% means that 40% of your blood volume is made up of red blood cells.
Why is Hematocrit Important?
Red blood cells are essential for transporting oxygen from the lungs to tissues and organs. The hematocrit value gives doctors important information about:
- Oxygen-carrying capacity: Indicates how effectively your blood can deliver oxygen.
- Hydration status: Can help assess fluid levels in the body.
- Overall health: Helps diagnose and monitor conditions like anemia, dehydration, or polycythemia.
Normal Hematocrit Ranges
Hematocrit levels vary by age, gender, and physiological state:
- Men: 41%–50%
- Women: 36%–44%
- Children: 32%–44%
- Newborns: 45%–61%
What Can Cause Abnormal Hematocrit Levels?
Low Hematocrit (Anemia)
A low hematocrit means there are fewer red blood cells than normal, which can lead to symptoms like fatigue, weakness, and shortness of breath. Common causes include:
- Iron deficiency anemia
- Vitamin B12 or folate deficiency
- Chronic diseases (e.g., kidney disease, cancer)
- Blood loss (e.g., from injury, heavy menstrual bleeding, or ulcers)
- Bone marrow disorders (e.g., aplastic anemia)
High Hematocrit (Polycythemia)
A high hematocrit means there are more red blood cells than normal, which can thicken the blood and increase the risk of clots. Common causes include:
- Dehydration: Less plasma makes RBC volume appear higher.
- Living at high altitudes: The body produces more RBCs to compensate for lower oxygen levels.
- Chronic lung diseases (e.g., COPD)
- Smoking
- Polycythemia vera: A rare blood disorder causing overproduction of RBCs.
How is Hematocrit Measured?
Hematocrit is typically measured as part of a Complete Blood Count (CBC) test. The test involves:
- Drawing a blood sample.
- Spinning the blood in a centrifuge to separate its components (RBCs, plasma, and white blood cells/platelets).
- Measuring the volume of RBCs relative to the total blood volume.
When to Test Hematocrit Levels
Doctors may order a hematocrit test to:
- Diagnose or monitor anemia, dehydration, or blood disorders.
- Evaluate overall health during routine check-ups.
- Assess treatment effectiveness for conditions affecting red blood cell levels.
Abnormal hematocrit levels usually require further investigation to identify and treat the underlying cause.
