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

• measure the severity of anemia (too few red blood cells) or polycythemia (too many red blood cells), 
• monitor the response to treatment, and 
• help make decisions about blood transfusions.

The hemoglobin test is normally ordered as a part of the complete blood count (CBC) (which is ordered for many different reasons) and before surgeries when a blood transfusion is anticipated. The test is also repeated in patients who have ongoing bleeding problems.

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 be the result of: 

• anemia (caused by iron deficiency), 
• inherited hemoglobin defects, 
• cirrhosis of the liver (during which the liver becomes scarred), 
• excessive bleeding, 
• vitamin and mineral deficiencies, 
• kidney disease, 
• other chronic illnesses, or 
• cancers that affect the bone marrow.

PLEASE NOTE: Numerically reported test results are interpreted according to the test's reference range, which may vary by the patient's age, sex, as well as the instrumentation or kit used to perform the test. A specific result within the reference (normal) range – for any test – does not ensure health just as a result outside the reference range may not indicate disease. To learn more about reference ranges, please see the article, Reference Ranges and What They Mean. To learn the reference range for your test, consult your doctor or laboratorian. Lab Tests Online recommends you consult your physician to discuss your test results as a part of a complete medical examination.

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. This is your body’s response to the decreased oxygen available at these heights.

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