Hematocrit is the
amount of red blood cells in your blood. Red blood cells are vital to your
health. Imagine them as the subway system of your blood. They transport oxygen
and nutrients to various locations in your body. Your body relies on the
correct proportion of red blood cells for you to stay healthy.
Your doctor may
order a hematocrit, or Hct, test if they think you have too few or too many red
Why Would You Get a Hematocrit Test?
A hematocrit test
can help your doctor diagnose you with a particular condition or it can help
determine how well your body is responding to a certain treatment. The test can
be ordered for a variety of reasons, but it’s most often used to test for:
- dietary deficiencies
If your doctor
orders a complete blood count (CBC) test, the hematocrit test is
included. Other tests in a CBC are a hemoglobin and reticulocyte count. Your
doctor will look at your overall blood test results to gain an understanding of
your red blood cell count.
How Is the Hematocrit Test Performed?
A medical provider
will need a small sample of blood to test your hematocrit. This blood can be
drawn from a finger prick or taken from a vein in your arm.
If the hematocrit
test is part of a CBC, a lab technician will draw blood from a vein, typically
from the inside of your elbow or from the back of your hand. The technician
will clean the surface of your skin with an antiseptic and place an elastic
band, or tourniquet, around your upper arm to help the vein swell with blood.
They’ll then insert
a needle in the vein and collect a blood sample in one or more vials. The
technician will remove the elastic band and cover the area with a bandage to
stop the bleeding. A blood test can be slightly uncomfortable. When the needle
punctures your skin, you might feel a prick or pinching sensation. Some people
also feel faint or lightheaded when they see blood. You may experience minor
bruising, but this will clear up within a few days. The test will take only a
few minutes. You can resume everyday activities after testing. Your sample will be sent to a lab for
In the laboratory,
your hematocrit is evaluated using a centrifuge. A centrifuge is a machine that
spins at a high rate to cause the contents in your blood to separate. A lab
specialist will add a special anticoagulant to keep your blood from clotting.
When the test tube
is taken out of the centrifuge, it will have settled into three parts:
- red blood cells
- plasma or fluid in your blood
Each will settle at
different parts of the tube, with the red blood cells moving to the bottom of
the tube. The red blood cells are then compared to a guide that tells what
proportion of your blood they make up.
How Are the Results of a Hematocrit Test
laboratory that tests the blood sample may have its own ranges, generally
accepted ranges for hematocrit depend on your gender and age. Typical ranges are as follows:
- adult men: 38.8 to 50 percent
- adult women: 34.9 to 44.5 percent
Children ages 15
and under have a separate set of ranges as their hematocrit level changes
rapidly with age. The specific lab that analyzes the results will determine the
normal hematocrit range for a child of a certain age.
Low or High Levels
If your hematocrit
levels are too high or too low, it can indicate various problems.
levels can indicate:
- bone marrow diseases
- chronic inflammatory disease
- deficiencies in nutrients such as
iron, folate, or vitamin B-12
- internal bleeding
- hemolytic anemia
- kidney failure
- sickle cell anemia
levels can indicate:
- congenital heart disease
- dehydration kidney tumor
- lung diseases
- polycythemia vera
Before getting the
test, let your doctor know if you've recently had a blood transfusion or are
pregnant. Pregnancy can decrease your blood urea nitrogen (BUN) levels due to
increased fluid in your body. A recent blood transfusion can also affect your
results. If you live at a high altitude, your hematocrit levels tend to be
higher due to reduced amounts of oxygen in the air.
Your doctor will
likely compare the results of your hematocrit test to the other parts of the
CBC test and your overall symptoms before making a diagnosis.
What Are the Risks of a Hematocrit Test?
A hematocrit test
is not associated with any major side effects or risks. You may have some
bleeding or throbbing at the site where the blood is drawn. Let your doctor
know if you experience any swelling or bleeding that doesn’t stop within a few
minutes of pressure being applied to the puncture site.