What is hematocrit? Definition, functions, and its importance in health

Hematocrit is an essential blood test that measures the proportion of red blood cells (RBCs) in your blood and plays a crucial role in diagnosing various medical conditions. This article explores the definition of hematocrit, and the procedure for measuring hematocrit.

In addition, the hematocrit normal range across different population groups and the conditions associated with high or low hematocrit levels will be discussed.

What is hematocrit?

The term hematocrit is derived from the English prefix hemato- (used to refer to blood) and the Greek word krites (judge), meaning “to judge the blood”.

The hematocrit definition is the volume of red blood cells in the blood, as a percentage of total blood volume. For example, if a person has 40 millilitres (ml) of red blood cells in 100 ml of blood, their hematocrit is 40%.

This simple test is used to identify health conditions and to monitor the response to treatments. Once a blood sample is taken, a glass tube and a centrifuge are sufficient to measure hematocrit.

A hematocrit is commonly included in a complete blood count (CBC) to assess overall health and detect conditions such as anemia, dehydration, and polycythemia (too many red blood cells in the blood).

Normal hematocrit levels vary based on factors like age, sex, and altitude.

Importance of hematocrit in health and the medical industry

As previously explained, hematocrit levels reflect the percentage of red blood cells (RBCs) in blood compared to plasma.  But why is this relevant? RBCs are essential for oxygen transport. They contain a protein called hemoglobin that is the responsible for delivery of oxygen to the tissues. Even though the concentration of hemoglobin can be measured directly apart from hematocrit, to better evaluate the real oxygen-carrying capacity of the blood, the hematocrit is still a critical parameter to assess the overall health of a patient’s blood.

Among the many insights it provides, the hematocrit offers information regarding:

• Oxygen transport: A normal or slightly high hematocrit usually supports better oxygen delivery to tissues. Oxygen is essential for cell metabolism, muscle function, and overall energy production.
• Diagnosis of dehydration: A high hematocrit may indicate dehydration due to reduced plasma volume. This can be an early warning sign in individuals exposed to extreme heat, illness, or strenuous physical activity.
• Disease detection: Causes of a low hematocrit include iron deficiency anemia, chronic disease, or blood loss, while high hematocrit may be linked to polycythemia (presence of too many red cells), lung disease, or conditions that affect bone marrow function.
• Treatment monitoring: Hematocrit is used to track progress in patients receiving iron therapy, chemotherapy, or blood transfusions. It helps determine whether treatments are effective in restoring normal red blood cell levels.
• Cardiovascular health: Abnormal hematocrit levels are associated with increased risk of cardiovascular diseases. A high hematocrit may contribute to increased blood viscosity, raising the likelihood of clot formation, while low levels may indicate an insufficient supply of oxygen to heart tissues.
• Hematocrit and altitude adaptation: Individuals living at high altitudes naturally have higher hematocrit levels to compensate for lower oxygen availability in the air. This physiological adjustment helps prevent altitude sickness and improves oxygen utilization.

Hematocrit can be useful in sports medicine, particularly in endurance sports where oxygen delivery plays a major role in performance and recovery. Monitoring hematocrit levels can help prevent overtraining and detect conditions like blood doping.

Classifications of hematocrit levels

Hematocrit levels vary due to multiple factors, including age, sex, altitude and medical conditions. That’s why normal hematocrit is a range not a specific number.

Normal hematocrit levels

Below you’ll find the hematocrit levels traditionally considered normal in relation to population standards.

• Men: 38.3% - 48.6%
• Women: 35.5% - 44.9%
• Children: 32% - 44%
• Pregnancy: Typically lower due to increased plasma volume, which dilutes the red blood cell concentration.

Abnormal hematocrit levels

High hematocrit

• Causes:
  • Dehydration, which reduces plasma volume and makes the red blood cell proportion appear elevated.
  • Lung disease, such as chronic obstructive pulmonary disease (COPD), which leads to increased RBC production as the body attempts to compensate for low oxygen levels.
  • High altitude adaptation, which naturally raises hematocrit to improve oxygen delivery in low-oxygen environments.
  • Overproduction of erythropoietin (EPO), a hormone that stimulates red blood cell overproduction (polycythemia).
• Symptoms:
  • Dizziness
  • Headaches
  • Flushed skin
  • Increased risk of blood clot formation, leading to complications such as stroke or deep vein thrombosis (DVT).

Low hematocrit

• Causes:
  • Blood loss from injury, surgery, or gastrointestinal bleeding.
  • Iron, vitamin B12, or folate deficiency, can make you have fewer RBC.
  • Chronic kidney disease, where the kidneys fail to produce enough erythropoietin, a hormone that stimulates the production of RBC. Then, it results in reduced RBC production.
  • Autoimmune disorders that destroy RBC (hemolytic anemia)
  • Increased plasma volume due to pregnancy, excess protein production or overhydration.
• Symptoms:
  • Fatigue and weakness
  • Pale skin
  • Shortness of breath
  • Cold hands and feet

Conditions affecting hematocrit levels require testing for hemoglobin levels, serum iron, and bone marrow function.

How hematocrit is measured：process and functionality

Step 1: Blood sample collection

A blood sample is drawn from a vein or via a finger prick into a special thin glass tube.

Step 2: Hematocrit measurement methods

• Microhematocrit test: Centrifuging blood to separate plasma and RBCs.
• Automated hematology analyzers: Common in modern labs for precise results.
• Point-of-care testing: Portable devices for rapid assessment of hematocrit.

Step 3: Hematocrit calculation formula

Hematocrit (%) = (Volume of RBCs / Total blood volume) × 100

Clinical applications of hematocrit

• Diagnosis: Used in detecting anemia, polycythemia, and cardiovascular issues.
• Sports medicine: Helps monitor athlete hematocrit levels to keep them at a normal range and prevent overtraining or to look for signs of blood doping.
• Cardiovascular health: High hematocrit can indicate increased blood viscosity, impacting the risk of developing clots or experiencing heart failure.

Knowing when to get a hematocrit test ensures early detection of potential health risks.

Limitations of the hematocrit testing

The limitations are:

• Hydration effects: Dehydration falsely elevates hematocrit levels, while overhydration lowers them.
• Altitude impact: Long-term exposure to high altitudes naturally increases hematocrit levels.
• Test accuracy: Hematocrit blood test accuracy depends on sample handling and lab techniques.
• Chronic diseases: Conditions like kidney disease affect hematocrit.
• Lifestyle factors: Smoking, diet, and exercise can alter hematocrit readings.

Nonetheless, hematocrit remains a highly valuable diagnostic test, as it offers a fast and straightforward snapshot of the overall condition of the blood.

In conclusion, hematocrit is a vital health marker that reflects the blood’s capacity to transport oxygen, assess hydration levels, and aid in diagnosing various medical conditions. Regular monitoring can help detect issues such as anemia, polycythemia, and cardiovascular risks. Through routine testing and healthy lifestyle choices, individuals can maintain optimal hematocrit levels and support overall well-being.

Want to learn more about related topics? Explore our medical glossary here.