Hemoglobin and Hematocrit Tests

At a Glance

Also known as

Hgb, Hb, Hct, Crit, Packed cell volume (PVC), H&H

Related tests

Complete blood count

Why get tested?

If you have anemia, polycythemia, or dehydration

When to get tested?

As part of a complete blood count (CBC), which may be ordered for a variety of reasons

Sample required

A blood sample drawn from a vein in your arm or by a fingerstick (children and adults) or heelstick (newborns)

The Test Sample

What is being tested?

This test measures the amount of hemoglobin, a protein found in red blood cells, in a blood sample, which is a good indication of the blood’s ability to deliver oxygen to tissues and organs and to transport the waste product carbon dioxide to the lungs, where it is exhaled. If your hemoglobin levels are low, you may have anemia, a condition in which your body is not getting enough oxygen, causing fatigue and weakness.

The hemoglobin rises when the number of red blood cells increases. The hemoglobin falls to less than normal, indicating anemia, when your body decreases its production of red blood cells, increases its destruction of red blood cells, or if blood is lost due to bleeding.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in your arm or by a fingerstick (for children and adults) or heelstick (for newborns).

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

The hemoglobin test is an integral part of your health evaluation. The test is used to:

• measure the severity of anemia or polycythemia,

• monitor the response to treatment of anemia or polycythemias, and

• help make decisions about blood transfusions if the anemia is severe.

When is it ordered?

The hemoglobin test is normally ordered as a part of the complete blood count (CBC) , which is ordered for many different reasons, including for a general health screen. The test is also repeated in patients who have ongoing bleeding problems or chronic anemias or polycythemia.

What does the test result mean?

Normal values in an adult are 12 to 18 grams per deciliter (100 milliliters) of blood. Above-normal hemoglobin levels may be the result of:

• dehydration,

• excess production of red blood cells in the bone marrow,

• severe lung disease, or

• several other conditions.

Below-normal hemoglobin levels may lead to anemia that can be the result of:

• iron deficiency or other deficiencies, such as B12 and folate,

• inherited hemoglobin defects, such as sickle cell anemia or thalassemias,

• other inherited conditions, such as enzyme defects,

• cirrhosis of the liver,

• excessive bleeding,

• excessive destruction of red blood cells,

• kidney disease,

• other chronic illnesses,

• bone marrow failure or aplastic anemia, or

• cancers that affect the bone marrow.

Is there anything else I should know?

Hemoglobin decreases slightly during normal pregnancy.

Hemoglobin levels peak around 8 a.m. and are lowest around 8 p.m. each day.

Heavy smokers have higher hemoglobin levels than nonsmokers.

Living in high altitudes increases hemoglobin values due to an increase in the number of red blood cells. Your body produces more red blood cells in response to the decreased oxygen available at these heights.

Hemoglobin levels are slightly lower in older men and women and in children.

Common Questions

1. Does exercise affect hemoglobin levels?

   No, except that dehydration can temporarily increase hemoglobin levels.

2. Is anyone at greater risk of abnormal hemoglobin levels?

   Women of childbearing age may have temporary decreases during menstrual periods and pregnancy.

3. Are there warning signs for abnormally low hemoglobin levels?

   Some warning signs are fatigue, fainting, pallor (loss of normal skin color), and shortness of breath.

4. Can a healthy diet and nutrition help keep optimal hemoglobin levels?

   A healthy diet containing vegetables and foods high in iron can be beneficial.