The Difference Between Hemoglobin and Hematocrit

Hemoglobin and hematocrit are both red blood cell measurements that are used to help diagnose nutritional deficiencies, acute illnesses, and chronic medical conditions. Hemoglobin is a protein in the red blood cells (RBCs), and hematocrit reflects the percentage of blood volume that is composed of red blood cells.

The values for hemoglobin and hematocrit are reported as part of a complete blood count (CBC) test. Read on to learn what these levels mean and why they are important. 

What Is Hemoglobin? 

Hemoglobin is an iron-containing protein that carries oxygen and carbon dioxide. It is located inside the red blood cells. The hemoglobin protein changes its three-dimensional shape in response to changes in the surrounding pH and temperature. 

In the lungs, hemoglobin binds tightly to oxygen and releases carbon dioxide due to the slightly cooler body temperature and slightly less acidic pH.

Additionally, there is a high oxygen concentration in the lungs and a low carbon dioxide concentration, which causes oxygen to move toward hemoglobin, increasing the amount of oxygen that is bound to hemoglobin. 

In the cells of the body’s organs and tissues, the pH is slightly acidic, and the temperature is slightly warmer. The cellular environment causes hemoglobin to change its shape in a way that makes it more likely to bind to carbon dioxide (which is a waste product of active cells) and to release oxygen (which the cells need).

What Is Hematocrit? 

Hematocrit is a measure of the proportion of blood that is composed of red blood cells. Blood contains plasma (the liquid part that also contains hormones, nutrients, and electrolytes), red blood cells, platelets, and white blood cells.

The proportion of each of these components should be within a certain range. Abnormalities in the concentration of any of these important materials can indicate health problems. 

Measuring Red Blood Cells 

There are several measures that are used to assess how many red blood cells your body has and how well they are functioning. In addition to hemoglobin and hematocrit, a CBC also measures these aspects of red blood cells:

• Red blood cell count: The number of RBCs per unit of volume
• Mean corpuscular volume (MCV): The average size of the red blood cells
• Mean corpuscular hemoglobin: The average amount of hemoglobin per red blood cell
• Mean corpuscular hemoglobin concentration: The average amount of hemoglobin in a given volume of red blood cells
• Red cell distribution width: The variation in size of red blood cells in a sample
  

Other cellular parts of the blood that are measured in a CBC include:

• Platelet count (cells needed for blood clotting)
• White blood cell count (cells that defend against infection)
• White blood cell differential (counts of different types of white blood cells)

These values provide a comprehensive idea about the size and function of the cells in the blood. In addition, a blood smear may be made and read by a lab professional to further assess the red blood cells and perform a detailed white blood cell differential.

Normal Ranges 

There are established values for normal hemoglobin and hematocrit, and these values differ by age.

When Levels Are Low 

Usually, low hemoglobin or low hematocrit means that you are not producing enough red blood cells or that you are losing red blood cells due to acute bleeding, a bleeding disorder, or accelerated destruction of red blood cells.

Low red blood cell production can occur due to nutritional deficiencies, disease, or medications, especially certain kinds of chemotherapy. Iron deficiency causes low hemoglobin and hematocrit because iron is a component of hemoglobin. Aplastic anemia is a bone marrow disorder in which the body produces fewer blood cells.

Often, hemoglobin can be low during pregnancy. This may need to be treated with iron supplements.

When Levels Are High 

Hemoglobin and hematocrit can be elevated due to some medical conditions. Sometimes this occurs as a compensatory response to low oxygen levels, and sometimes the body makes too many red blood cells due to illness, such as cancer, heart disease, and lung disease. Smoking increases hemoglobin and hematocrit.

Polycythemia vera is a disorder that causes increased production of red blood cells. Additionally, dehydration can make your hemoglobin and hematocrit seem higher than they really are because of low blood volume.

Reasons for a Complete Blood Count (CBC)

A CBC is often part of a routine medical checkup. You might also have a CBC before having a surgical procedure as part of your preoperative testing. Often, a CBC is necessary before starting certain medical therapies.

Your healthcare professional might order this test if you have signs or symptoms of a medical condition, such as an infection, inflammation, blood loss, or cancer. Some of the indications for having a CBC include: 

• Fever 
• Bleeding 
• Low blood pressure 
• Unexplained weight loss
• Feeling unusually tired, cold, or dizzy
  

Summary 

Hemoglobin and hematocrit are both part of a complete blood count (CBC). These values help your medical team evaluate your red blood cell number and function. They can be too high or too low due to many different conditions, including bleeding, iron deficiency, polycythemia vera, and more.

A Word From Verywell

If you have a CBC as part of routine screening, because of symptoms you are having, or to monitor a medical condition, your results can help determine whether you need medical treatment or further tests. Often, abnormalities are flagged in red or bolded in the laboratory report.

It can be helpful for you to see your numbers, but sometimes these readings can cause unnecessary anxiety. Your results should be considered in relation to your overall health, symptoms, and trends in your measurements over time.

Talk to your doctor if you have any concerns about your hemoglobin or hematocrit. Abnormalities can usually be corrected with treatment, which helps prevent health complications.