Patient education: Hemoglobin and hematocrit tests (The Basics)

What are hemoglobin and hematocrit tests? — Hemoglobin is a protein found in red blood cells. It helps the cells carry oxygen to all parts of the body. Hematocrit is the percentage of the blood that is made up of red blood cells. Hemoglobin and hematocrit are usually measured as part of a blood test called a "complete blood count," or "CBC."

●If your hemoglobin or hematocrit is low, this is called "anemia." Anemia can happen for a few different reasons, including:

•Not having enough iron

•Bleeding

•Kidney disease or other chronic health problems

●If your hemoglobin or hematocrit is high, this is called "polycythemia." This can happen for a few different reasons, including:

•Dehydration

•Conditions that lower the blood oxygen level, like lung disease or sleep apnea

•Testosterone replacement therapy, if given as shots

•A condition called "polycythemia vera"

•Kidney or liver cancer

Why might I get a hemoglobin and hematocrit test? — Your doctor might order these tests:

●If you have symptoms of anemia – These can include feeling tired or short of breath, having very little energy, headaches, or depression.

●If you have symptoms of low iron levels – These can include restless legs or craving ice.

●If you are at increased risk of anemia – Things that increase your risk include heavy periods, pregnancy, giving blood frequently, or certain medical conditions.

●If you take certain medicines that can lower hemoglobin

●To monitor treatment of anemia to make sure that it is working

●If you have symptoms of polycythemia – These can include headache, dizziness, vision problems, itchy skin, pain in the hands or feet, or belly pain.

●To monitor treatment of polycythemia to make sure that it is working

How do I prepare for a hemoglobin and hematocrit test? — For these tests, you need to get a "blood draw." Your doctor or nurse will tell you where to go for this.

It might help to wear a short-sleeve shirt to your blood draw appointment. This makes it easier for the person drawing your blood to get to your arm.

What happens during a blood draw? — For the blood draw, a needle is used to take a small amount of blood from your arm (figure 1). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Most of the time, getting blood taken does not cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

If your hemoglobin or hematocrit is too low or too high, your doctor or nurse will talk to you about what to do next. They might need to do more tests to figure out the cause.

If you do have a health problem, your doctor will work with you to come up with a plan for treatment.

More on this topic

Patient education: Complete blood count (CBC) (The Basics)
Patient education: Anemia caused by low iron (The Basics)
Patient education: Polycythemia vera (PV) (The Basics)
Patient education: Anemia overview (The Basics)

Patient education: Anemia caused by low iron in adults (Beyond the Basics)