Hemoglobin: structure, function, abnormal levels.


Hemoglobin plays a vital role in your body. It is a protein in red blood cells (erythrocytes) that carries oxygen from the lungs to all tissues and organs. Therefore, any abnormality in the level or structure of hemoglobin can cause serious symptoms.

Symptoms associated with hemoglobin abnormalities can include fatigue, heart palpitations, pale skin, and more. If you have any of these problems, your healthcare provider will begin a diagnostic process to determine the cause and may order a hemoglobin test .


Hemoglobin is a protein made up of four chains of amino acids. Each of these chains contains heme, a compound that contains iron and carries oxygen into the bloodstream.

Hemoglobin is responsible for the shape of red blood cells, which generally resemble donuts, but with a thin center rather than a hole. In conditions associated with abnormal hemoglobin, such as sickle cell anemia, the abnormal shape of the red blood cells can lead to problems.

The pigment in hemoglobin is responsible for the red color of the blood.


Hemoglobin binds and carries oxygen from the capillaries in the lungs to all tissues in the body. It also plays a role in the transport of carbon dioxide from body tissues to the lungs.

Nitric oxide and carbon monoxide can also bind to hemoglobin. Carbon monoxide binds to hemoglobin much more easily than oxygen, and its presence actually prevents oxygen from binding to hemoglobin. This is why carbon monoxide poisoning is so serious.

Low hemoglobin conditions

Low hemoglobin levels are often called anemia . Causes of anemia can include anything that affects the level or function of hemoglobin or red blood cells.

Causes of low hemoglobin include:

  • Blood loss: This can occur due to surgery, heavy menstruation, bleeding in the gastrointestinal tract, or any other form of bleeding. Premenopausal women have lower hemoglobin levels than men due to menstruation.
  • Lack of production: decreased production of cells in the bone marrow may be due to a deficiency in the bone marrow (eg, aplastic anemia) or infiltration of the bone marrow by cancers such as leukemia, lymphoma, or solid tumors such as metastatic breast cancer. …
  • Hemolysis (breakdown of red blood cells): Blood cells can become hemolyzed due to conditions such as severe infections, toxins, and malaria.
  • Nutritional deficiency: Iron deficiency, vitamin B12 deficiency, and folate deficiency can cause anemia.
  • Kidney disease: Healthy kidneys secrete erythropoietin, a hormone that promotes the production of red blood cells.
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Conditions with high hemoglobin

Several conditions are associated with elevated hemoglobin levels, including:

  • Lung diseases such as COPD and pulmonary fibrosis.
  • Congenital heart disease (present at birth)
  • Right ventricular failure (cor pulmonale)

In these cases, the increase in hemoglobin is the result of a mechanism to compensate for the lack of oxygen in the body.

A hemoglobin test can show artificially elevated hemoglobin levels due to dehydration. In this situation, hemoglobin is more concentrated when there is little fluid in the body.

Hemoglobin can also be elevated in people who live at high altitudes due to the presence of oxygen in the atmosphere.

Abnormal hemoglobin

Conditions in which hemoglobin is abnormal include:

  • Sickle cell anemia : This is an inherited disorder in which abnormal hemoglobin leads to the formation of sickle-shaped red blood cells. They can lodge in blood vessels, causing pain, blood clots, and an increased risk of stroke.
  • Thalassemia : These inherited diseases are characterized by different types of abnormal hemoglobin. Both alpha thalassemia and beta thalassemia are of many different types, and symptoms range from none to severe.

People with thalassemia often have lifelong anemia and may need frequent blood transfusions. Thalassemia intermedia is also called "transfusion independent thalassemia" and can only be detected in adulthood.

Hemoglobin level assessment

Hemoglobin levels are usually measured as part of a complete blood count (CBC) . Other lab test results can also help determine the cause of hemoglobin problems.

This includes:

  • Total red blood cell count
  • Red blood cell indices such as MCHC (mean corpuscular hemoglobin concentration), MCH (mean corpuscular hemoglobin), and MCV (mean corpuscular volume)
  • Serum ferritin level , which measures iron stores in the body.

Normal hemoglobin ranges

Normal hemoglobin levels depend on age and gender. They are measured in grams per deciliter (g / dl).

  • Adult male : 13.8-17.2 g / dl
  • Adult female: 12.1-15.1 g / dl

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If you hear about hemoglobin, you might think about bleeding, especially heavy menstrual bleeding. However, there is a wide range of diseases that can cause both high and low hemoglobin levels. Also, abnormal hemoglobin types can contribute to the development of the disease.

To determine the cause of high or low hemoglobin, your healthcare provider will ask you questions, perform a physical exam, and evaluate other blood tests along with your hemoglobin level.

Frequently asked questions

  • Fatigue is the number one sign. It is caused by anemia, a blood disorder caused by a lack of hemoglobin, an essential protein found in red blood cells. Other symptoms may include headache, dizziness, weakness, pale skin, feeling cold, and shortness of breath.

  • Intense training, especially among endurance athletes, can cause a condition called "sports anemia." It is not anemia that causes fatigue and requires iron supplements. Sports anemia is associated with relatively low hemoglobin levels in well-trained athletes, which is the result of increased plasma volume. This has the beneficial effect of allowing the blood to circulate oxygen better during exercise.

  • A blood test, called electrophoresis, measures the types of hemoglobin in your blood and detects abnormal hemoglobin, including:

    • HgbS: associated with sickle cell anemia.
    • HgbC: causes mild anemia
    • HgbE: causes mild anemia

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