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

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.

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.

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.