Hematocrit is the percentage of red cells in your blood. Blood consists of white blood cells, red blood cells, platelets, and blood plasma, which is the liquid part of the blood.
When hematocrit levels fall below the usual range, meaning that the person has too few red cells, it is called anemia. When hematocrit levels rise above the usual range, meaning that the person has too many red cells, it is called polycythemia or erythrocytosis.
Hematocrit levels vary depending on age and sex. Doctors typically check hematocrit levels if you are showing signs or symptoms of anemia, polycythemia, or erythrocytosis. These levels may also be checked as part of a routine medical exam or before you give a blood donation.
The hematocrit test is part of a standard blood test called a complete blood count (CBC), which measures the different components of your blood.
For the test, a phlebotomist or another healthcare professional inserts a small needle into a vein in your arm and withdraws a small sample of blood. The sample goes to a laboratory where a technician measures the levels of hematocrit and other blood components.
The hematocrit test usually only takes 5 minutes to perform, and you do not have to do anything to prepare.
If you are getting other tests done alongside the hematocrit test, your doctor may ask you not to eat or drink anything for 8 hours before the test. However, if you are only getting your hematocrit level checked, you may eat and drink before the test.
You may feel a mild sting as the needle enters your arm, but the test is relatively painless. There is a small risk of bruising at the site where the needle is inserted, but this is not common.
Doctors typically test hematocrit levels as part of a CBC when you get your yearly physical. It is also done before you give a blood donation or receive a blood transfusion. If you are showing signs or symptoms of anemia (too few red blood cells) or polycythemia or erythrocytosis (too many red blood cells), your doctor will likely want to check your hematocrit level.
Symptoms of anemia include:
- pale skin
- shortness of breath
- weakness or fatigue
- cold hands and feet
- headache
- dizziness
Symptoms of polycythemia and erythrocytosis include:
- excessive sweating
- flushed skin
- itching
- tiredness
- shortness of breath
- headache
- blurred or double vision
You do not need to do any special preparations for the hematocrit test. You can expect the blood draw to be quick and relatively painless. Bruising in the area is uncommon but possible.
Results typically come back within 1–2 days. Your doctor will discuss your results with you and order any necessary further testing.
Hematocrit levels differ depending on age and sex. For adults, the usual hematocrit levels are 41–50% for males and 36–48% for females.
For children, a typical hematocrit level is 30–44%, depending on their age.
If you have been experiencing any unusual symptoms, your doctor may want to check your hematocrit level to make sure it is falling within the typical range.
If your hematocrit level is low, it means that you have too few red blood cells in your body. Some conditions that can cause a low hematocrit level include:
- anemia
- malnutrition
- bleeding
- the destruction of red blood cells, or hemolysis
- certain cancers, such as leukemia, lymphoma, and multiple myeloma
- kidney disease
- too much water in the body
- too little iron, folate, vitamin B6, and vitamin B12 in the diet
If your hematocrit level is high, it means that you have too many red blood cells in your body. Some conditions that can cause a high hematocrit level include:
- congenital heart disease
- dehydration
- polycythemia vera, which is a type of blood cancer
- right sided heart failure
- bone marrow disease
- low oxygen levels in the blood
- scarring or thickening of the lungs
Certain factors can affect hematocrit levels and the accuracy of the test. Some of these factors include:
- hydration status
- pregnancy
- a recent blood transfusion
- high altitudes
- endurance sports
If any of these factors apply to you, be sure to make your doctor aware before getting your hematocrit level checked so that they can take this into consideration when reviewing the results.
The hematocrit test is part of a CBC. It measures the percentage of red cells in your blood.
Doctors usually perform this test yearly with a routine physical or to evaluate signs or symptoms. It is also common before donating blood or receiving a blood transfusion.
Sometimes, a hematocrit level that is high or low can indicate an underlying medical condition. Talk with your doctor if you are interested in getting your hematocrit level checked.
