What Does a Hematocrit Test Measure?
A hematocrit test is a blood test that measures the level of red blood cells in your blood.
Your blood is made up of plasma and blood cells. Plasma is the liquid part of your blood and is made of protein, salts, and water. Over half your blood composition is plasma.
Suspended in that plasma are three types of blood cells:
- Platelets, also called thrombocytes, are small fragments that help your blood clot so you stop bleeding.
- Red blood cells are the most abundant type of blood cell in your blood. They’re round with a slightly indented center and contain a protein called hemoglobin. Hemoglobin carries oxygen and removes carbon dioxide.
- White blood cells are part of your immune system. These cells are round with a distinct center. Their job is to fight off invaders by producing antibodies.
Hematocrit tests measure how much of your blood is red blood cells and determines if that amount is normal.
The test can help your doctor diagnose conditions like anemia, which is a low red blood cell count, and polycythemia, a high red blood cell count. It's a simple test that you have in your doctor's office or lab.
Normal Hematocrit Range
Hematocrit ranges can vary from person to person. Some things that can affect hematocrit levels are:
- Age
- Race
- Sex
But, in general, normal levels are:
- For men and people assigned male at birth: 38.3% to 48.6%
- For women and people assigned female at birth: 35.5% to 44.9%
Low Hematocrit
Low hematocrit is often caused by anemia, which is when you don’t have enough red blood cells to carry oxygen to your tissues.
There are several different types of anemia. The most common type is iron deficiency anemia. Your bone marrow produces blood cells, and it needs iron to make hemoglobin. If you’re low in iron, your body can’t make enough hemoglobin for your red blood cells. This type of anemia is common if you're pregnant of have lost a lot of blood.
Other types of anemia include:
Aplastic anemia. This is when your bone marrow doesn't make enough red blood cells. It can be caused by many things such as infectious diseases, certain medications, and exposure to toxins.
Hemolytic anemias. Hemolytic anemias happen when your red blood cells are destroyed faster than your body can replace them. You can be born with hemolytic anemia, or you can get it through some autoimmune disorders, cancers, infections, and viruses. Hemolytic anemia can also be acquired from an overactive spleen or a reaction to a blood transfusion.
Sickle cell anemia. Sickle cell anemia is a blood disorder that is passed down in your family. It causes your red blood cells to form in a crescent, or sickle, shape. This makes it harder for them to carry oxygen around your body.
Vitamin deficiency anemia (pernicious anemia). Your body needs vitamins, especially vitamin B12 and folate (B9), to produce healthy red blood cells. Low levels of these vitamins can make it hard for your body to make the red blood cells you need.
Symptoms of anemia include:
- Chest pain
- Cold hands and feet
- Dizziness or lightheadedness
- Fatigue
- Headaches
- Irregular heartbeat
- Pale or yellowish skin
- Shortness of breath
- Weakness
High Hematocrit
High hematocrit can be a sign of polycythemia, which is when you have too many red blood cells. This can cause your blood to become thicker and travel slower through your blood vessels and organs. There are two main types of polycythemia:
Primary polycythemia. This type is caused by a problem with your bone marrow cells that make red blood cells. It's often related to changes in genes.
Secondary polycythemia. This type happens when a health condition or environmental factor makes it hard for oxygen to reach your tissues. Your body reacts by increasing how many red blood cells it makes. This could be from things like smoking, staying at a high altitude, or congenital (from birth) heart disease.
Symptoms of polycythemia include:
- Bleeding problems like excessive bruising or bloody noses
- Blurry vision
- Confusion
- Dizziness
- Headaches
- Shortness of breath
- Tiredness
Hematocrit Test Procedure
The hematocrit test is done like any other blood test. The lab will likely draw blood from a vein in your arm or hand. To determine your hematocrit, the lab spins your blood sample at a high speed. This causes the plasma and blood cells to separate, and the heavier red blood cells sink to the bottom of the tube. The amount is measured to calculate what percentage of your blood is red blood cells.
Takeaways
A hematocrit test is one way your doctor can tell whether you have a health condition that affects your blood. A low hematocrit level is often a sign of anemia, and a high level of hematocrit can be a sign of polycythemia. A simple blood test will give your doctor more information so that they can diagnose your condition and make a treatment plan.