What Is Hemoglobin?
Picture of Hemoglobin A1c Chart
Hemoglobin (sometimes abbreviated as Hb) is a complex protein found in red blood cells that contains an iron molecule. The main function of hemoglobin is to carry oxygen from the lungs to the body tissues, and to exchange the oxygen for carbon dioxide, and then carry the carbon dioxide back to the lungs and where it is exchanged for oxygen. The iron molecule in hemoglobin helps maintain the normal shape of red blood cells.
How Is a Hemoglobin Test Measured?
Hemoglobin is the protein molecule in red blood cells that carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs.
Hemoglobin is routinely measured as part of a routine blood test termed blood count (CBC). A complete blood count is one of the most common tests doctors order for a patient. It is done on automated machines that use a blood sample that is chemically treated to release hemoglobin from red blood cells. The released hemoglobin then is bound chemically to cyanide which forms a compound that absorbs light. The amount of absorbed light is then measured, and this measurement is directly related to how much hemoglobin is present in the blood.
What Are Normal Hemoglobin Values?
The Normal Hemoglobin Levels by Age Group Chart.
Normal hemoglobin values are related to the person's age and sex. Normal values may vary slightly between test systems, and which groups of doctors have determined "normal values" for their group of patients; however, the value ranges are close (vary by about 0.5 g/dl) for almost every group. An example of normal ranges that are widely accepted by Family Practice physicians is as follows:
- Birth: 13.5 to 24.0 g/dl (mean 16.5 g/dl)
- Age <1 month: 10.0 to 20.0 g/dl (mean 13.9 g/dl)
- Age 1-2 months: 10.0 to 18.0 g/dl (mean 11.2 g/dl)
- Age 2-6 months: 9.5 to 14.0 g/dl (mean 12.6 g/dl)
- Age 0.5 to 2 years: 10.5 to 13.5 g/dl (mean 12.0 g/dl)
- Age 2 to 6 years: 11.5 to 13.5 g/dl (mean 12.5 g/dl)
- Age 6-12 years: 11.5 to 15.5 g/dl (mean 13.5)
- Age 12-18 years: 12.0 to 16.0 g/dl (mean 14.0 g/dl)
- Age >18 years: 12.1 to 15.1 g/dl (mean 14.0 g/dl)
- Age 12-18 years: 13.0 to 16.0 g/dl (mean 14.5 g/dl)
- Age >18 years: 13.6 to 17.7 g/dl (mean 15.5 g/dl)
What Does Low Hemoglobin Mean?
Low hemoglobin means that a person's hemoglobin level when measured, is below the lowest limits of normal for their age and sex (see the above-normal range of values). For example, a 19-year-old male would have low hemoglobin if the detected blood value was below 13.6 g/dl. Another term frequently used in place of low hemoglobin is anemia, or the person is described as being anemic. Some of the more common causes of anemia are as follows:
What Does High Hemoglobin Mean?
High hemoglobin levels mean that measured hemoglobin levels are above the upper limits of normal for the age and sex of the person (see the above-normal values). For example, a 19-year-old that has a detected hemoglobin level of above 17.7 g/dl would have a high hemoglobin level. Some causes for high hemoglobin levels are as follows:
What Is Anemia and What Are Its Symptoms?
Anemia is a term that means less than normal levels of red blood cells or hemoglobin in a person's blood. The term is derived from the Greek term anaimia, meaning lack of blood. The symptoms of anemia usually include some of the following:
Underlying causes that are responsible for the anemia often produce other symptoms that are more specific to the underlying cause.
What Is Hemoglobin S for Sickle Cell Disease?
Sickle cell disease is a genetic alteration that causes some hemoglobin molecules to be defective (the defective hemoglobin is termed hemoglobin S). When red blood cells have hemoglobin S, and are subjected to low oxygen levels, they can become crescent or "sickle-shaped" and do not easily move through capillary vessels with small diameters, thus depriving tissues of exchanging oxygen and carbon dioxide.
In extreme situations, tissue can begin to die. Sickle cells may lead to anemic conditions because sickle cells have a lifespan of about 10-20 days, while normal red blood cells live about 120 days; thus the bone marrow may fall behind in synthesizing new red blood cells. Moreover, dead or dying sickle cells may clog up the spleen as the spleen tries to remove the sickle cell debris from the blood. The common symptoms of sickle cell disease include the following in addition to other symptoms of anemia:
In some individuals, the spleen becomes so damaged that it needs surgical removal. Surgical removal of the spleen makes an individual more susceptible to certain diseases, most notably, pneumococcal pneumonia. Sickle cell disease is fully expressed in individuals that inherit a defective hemoglobin gene from each parent. The individual that inherits only one defective gene has much milder symptoms or no symptoms and is considered to have sickle cell trait, not sickle cell disease.
What Is Thalassemia?
Thalassemia is a genetic disease that is caused by one or more genes that control the production of either the alpha or beta protein that make up the structure of hemoglobin. A person has alpha or beta thalassemia; these two types have many subtypes but are usually grouped into one of two major subtypes termed thalassemia major and thalassemia minor.
Individuals with alpha or beta thalassemia major inherit defective genes from both parents, while those with thalassemia minor inherit defective genes from only one parent.
Most people with thalassemia minor may have small red blood cells but otherwise have almost no symptoms. Unfortunately, individuals with thalassemia major usually develop severe anemia during the first year of life and can develop facial abnormalities, growth failure, fatigue, and shortness of breath. Treatment for thalassemia major is frequent blood transfusions and in some individuals, bone marrow transplants.
What Is the Hemoglobin A1c Test?
The hemoglobin A1c test is a measure of the approximate glucose level that occurred in a person (usually a person with diabetes) over about a 3-month period by determining the person's percent of hemoglobin A1c. Hemoglobin A1c is also known as glycated hemoglobin; it is a form of hemoglobin made upon exposure of hemoglobin in the bloodstream to glucose.
- The hemoglobin A1c test is based on the fact that as blood sugar (glucose) increases, more sugar is bound to hemoglobin, and more glycated hemoglobin is formed.
- Hemoglobin A1c concentration is related to the average amount of glucose in the blood over about 3 months. Normal amounts of hemoglobin A1c are about 4%-5.9%.
- Hemoglobin A1c at 6% correlates to an average glucose level over 3 months of 135 mg/dl.
- Often, the recommended goal for a person with diabetes is 6.5% hemoglobin A1c (representing a glucose level of 152.5 mg/dl on average).
- Each 1% above 6% hemoglobin A1c represents an increase of 35 mg/dl of glucose.
- Consequently, detecting an 8% concentration of hemoglobin A1c would equal a glucose level of 135 plus 70 or 205 mg/dl average over 3 months.
- Concentrations of 8% or more indicate poor glucose control.
Reviewed on 11/1/2022
Nabili, Siamak N. MD, MPH. "Complete Blood Count." MedicineNet.com. Updated Jan 24, 2014.
Davis, Charles Patrick MD, PhD. "Hemoglobin." MedicineNet.com. Nov 4, 2015.
"Hemoglobin A1c." MedicineNet.com. Updated Apr 24, 2002.