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Hemoglobin: Normal, High, Low Levels and Causes

An illustration of hemoglobin carrying oxygen in red blood cells.
Hemoglobin also plays an important role in maintaining the shape of the red blood cells.Source: MedicineNet

What is hemoglobin?

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 made up of four protein molecules (globulin chains) that are connected together. The normal adult hemoglobin (abbreviated Hgb or Hb) molecule contains two alpha-globulin chains and two beta-globulin chains. In fetuses and infants, beta chains are not common and the hemoglobin molecule is made up of two alpha chains and two gamma chains. As the infant grows, the gamma chains are gradually replaced by beta chains, forming the adult hemoglobin structure.

Each globulin chain contains an important iron-containing porphyrin compound termed heme. Embedded within the heme compound is an iron atom that is vital in transporting oxygen and carbon dioxide in our blood. The iron contained in hemoglobin is also responsible for the red color of blood.

Hemoglobin also plays an important role in maintaining the shape of the red blood cells. In their natural shape, red blood cells are round with narrow centers resembling a donut without a hole in the middle. Abnormal hemoglobin structure can, therefore, disrupt the shape of red blood cells and impede their function and flow through blood vessels.

A laboratory testing vials of blood.
Hemoglobin is usually measured as a part of the routine complete blood count (CBC) test.Source: iStock

How is hemoglobin measured?

Hemoglobin is usually measured as a part of the routine complete blood count (CBC) test from a blood sample.

Several methods exist for measuring hemoglobin, most of which are done currently by automated machines designed to perform different tests on blood. Within the machine, the red blood cells are broken down to get the hemoglobin into a solution. The free hemoglobin is exposed to a chemical containing cyanide that binds tightly with the hemoglobin molecule to form cyanomethemoglobin. By shining a light through the solution and measuring how much light is absorbed (specifically at a wavelength of 540 nanometers), the amount of hemoglobin can be determined.

An illustration infographic chart of normal hemoglobin levels by age group.
The infographic chart of normal hemoglobin levels by age group.Source: MedicineNet

What are normal hemoglobin values?

The hemoglobin level is expressed as the amount of hemoglobin in grams (gm) per deciliter (dL) of whole blood, a deciliter being 100 milliliters.

The normal ranges for hemoglobin depend on the age and, beginning in adolescence, the gender of the person. The normal ranges are:

  • Newborns: 17 to 22 gm/dL
  • One (1) week of age: 15 to 20 gm/dL
  • One (1) month of age: 11 to 15 gm/dL
  • Children: 11 to 13 gm/dL
  • Adult males: 14 to 18 gm/dL
  • Adult women: 12 to 16 gm/dL
  • Men after middle age: 12.4 to 14.9 gm/dL
  • Women after middle age: 11.7 to 13.8 gm/dL

All of these values may vary slightly between laboratories. Some laboratories do not differentiate between adult and "after middle age" hemoglobin values. Pregnant females are advised to avoid both high and low hemoglobin levels to avoid increased risks of stillbirths (high hemoglobin – above the normal range) and premature birth or low-birth-weight baby (low hemoglobin – below the normal range).

A woman fatigued from doing chores with a graphic of normal and anemic levels of red blood cells.
A woman fatigued from doing chores with a graphic of normal and anemic levels of red blood cells. A low hemoglobin level is referred to as anemia or low red blood count.Source: MedicineNet

What does a low hemoglobin level mean?

A low hemoglobin level is referred to as anemia or low red blood count. A lower than a normal number of red blood cells is referred to as anemia and hemoglobin levels reflect this number. There are many reasons (causes) for anemia.

Some of the more common causes of anemia are:

Learn more about: B12

Higher than normal hemoglobin levels can be seen in people living at high altitudes and in people who smoke.
Higher than normal hemoglobin levels can be seen in people living at high altitudes and in people who smoke.Source: iStock

What does a high hemoglobin level mean?

Higher than normal hemoglobin levels can be seen in people living at high altitudes and in people who smoke. Dehydration produces a falsely high hemoglobin measurement that disappears when the proper fluid balance is restored.

Some other infrequent causes are high hemoglobin levels are:

  • advanced lung disease (for example, emphysema);
  • certain tumors;
  • a disorder of the bone marrow known as polycythemia rubra vera, and;
  • abuse of the drug erythropoietin (Epogen) by athletes for blood doping purposes (increasing the amount of oxygen available to the body by chemically raising the production of red blood cells).
A microscopic view of sickle cell disease.
Sickle cell disease is a genetic condition in which the quality of hemoglobin is defective. A microscopic view of sickle cell disease.Source: CDC

What is sickle cell disease?

Picture of Sickle Cell Red Blood Cell and Healthy Red Blood Cells
Picture of Sickle Cell Red Blood Cell and Healthy Red Blood Cells

Sickle cell disease is a genetic condition in which the quality of hemoglobin is defective. This condition can cause abnormal hemoglobin that can result in abnormally-shaped (sickled) red blood cells (see illustration). These abnormal red blood cells cannot easily pass through small blood vessels leading to inadequate oxygen for the tissues of the body.

Sickle cells also have a shorter life span than normal red blood cells (10 to 20 days compared to 120 days). This rapid turnover may result in the inadequate time to replace the red blood cells and may result in anemia.

In sickle cell anemia, one defective hemoglobin gene is inherited from each parent. If only one gene is inherited from one parent, then the condition is milder and referred to as sickle cell trait.

Symptoms of sickle cell anemia vary depending on its severity. Patients with sickle cell trait may experience mild if any, symptoms at all. In sickle cell disease, symptoms are more significant, especially in episodes of acute crisis. These symptoms can include:

An illustration of hemoglobin and red blood cell.
Thalassemia is a group of hereditary conditions with quantitative hemoglobin deficiency.Source: iStock

What is thalassemia?

Thalassemia is a group of hereditary conditions with quantitative hemoglobin deficiency. The body's failure to make globulin molecules will lead to a compensatory mechanism to make other less compatible globulin molecules. The different types of thalassemia are defined based on what type of globulin molecule is deficient. The severity of these conditions depends on the type of deficient globulin chain, the number of deficient globulins, and the severity of the underproduction. Mild disease may only present as mild anemia whereas severe deficiency may not be compatible with life.

Vials on top of a hemoglobin A1c test report.
Vials on top of a hemoglobin A1c test report.Source: iStock

What is the hemoglobin A1c test?

Hemoglobin A1c or glycosylated hemoglobin is a rough indication of blood sugar control in people with diabetes mellitus over the preceding 3 months. As more glucose (blood sugar) circulates in the blood on a daily basis, more glucose is bound to the circulating hemoglobin. Normal hemoglobin A1c levels range between 4% to 5.9%. As this number reaches 6% or greater, it signifies poorer diabetes control.

A hemoglobin A1c of 6% roughly correlates with an average blood sugar level of 135 mg/dL (milligrams per deciliters) over the previous 3 months. Each 1% increase in hemoglobin A1c above 6% represents an average blood sugar of approximately 35 mg/dL over 135 mg/dL. For example, a hemoglobin A1c measurement of 7% corresponds to an average blood sugar level of 170 mg/dL in the previous 3 months.

A woman eats an iron-rich healthy salad.
A woman eats an iron-rich healthy salad.Source: iStock

How can a person increase his or her hemoglobin level?

There are a number of ways to increase hemoglobin levels. In general, low hemoglobin levels that need to be increased are caused by three circumstances: decreased red blood cell production (for example, altered bone marrow hemoglobin production, iron deficiency), increased red blood cell destruction (for example, liver disease), and by blood loss (for example, trauma from a gunshot or knife wound). Addressing these underlying causes of low hemoglobin levels initially determines what method to use to increase hemoglobin levels.

Methods to increase hemoglobin levels are varied and their use depends on the underlying problems. Some of the ways to increase hemoglobin include:

  • transfusing red blood cells
  • receiving erythropoietin (a hormone used to stimulate red blood cell production in individuals with decreased red blood cell production or increased red cell destruction)
  • taking iron supplements
  • increasing the intake of iron-rich foods (eggs, spinach, artichokes, beans, lean meats, and seafood) and foods rich in cofactors (such as vitamin B6, folic acid, vitamin B12, and vitamin C) important for maintaining normal hemoglobin levels. Such foods include fish, vegetables, nuts, cereals, peas, and citrus fruits.

Individuals should not take iron supplements or other treatments for low hemoglobin levels without first discussing such treatments with their physician as side effects from these treatments and/or excess iron intake may cause additional problems. Also, iron supplements should be kept away from children as iron poisoning in young children can be fatal.