What Does High and Low Hemoglobin Mean?

What Is Hemoglobin?

Hemoglobin 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 present in hemoglobin helps maintain the normal shape of red blood cells.

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How Is a Hemoglobin Test Measured?

Hemoglobin is normally measured as part of a routine blood test termed blood count. A complete blood count (CBC) is one of the most common tests doctors order for a patient. It is performed on automated machines that use a blood sample that is chemically treated to release hemoglobin from red blood cells. The released hemoglobin is then chemically bound to cyanide that 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.

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What Are Normal Hemoglobin Values?

Normal hemoglobin values are related to the person’s age and sex. Normal values may differ a little between test systems, and which groups of doctors have determined normal values for their group of patients. But the normal value ranges are close (vary by about 0.5 g/dl) for almost every group. An example of normal ranges that is 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)
  • Female
    • 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)
  • Male
    • 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 the hemoglobin level of a person when measured, is below the lowest limits of normal for their age and sex (see above normal range of values). Another term frequently used in place of low hemoglobin is anemia. Some of the more common causes of anemia are as follows:

  • Nutritional deficiency such as iron, folic acid, or vitamin B 12 deficiency
  • Gastrointestinal blood loss (ulcers, colon cancer)
  • Kidney problems
  • Blood loss from surgery or trauma
  • Red Blood cell synthesis problems (bone marrow disorders, genetic disorders such as sickle cell anemia).
  •  Bone marrow suppression by exposure to radiation or chemotherapy

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. Some causes for high hemoglobin levels are as follows:

  • Cancer
  • Living at a high altitude
  • Lung disease
  • Tobacco smoking
  • Bone marrow disorders
  • Overdose or inappropriate use of epoetin alfa (Epogen, Procrit)
  • Blood doping (increasing RBC’s by using certain drugs)

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 symptoms:

  • Shortness of breath
  • Heart palpitations
  • Pale skin
  • Fainting
  • Restless legs syndrome
  • Weakness
  • Chest pain

Primary causes of anemia often produce other symptoms that are more precise to the underlying cause.

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What Is Hemoglobin S for Sickle Cell Disease?

Sickle cell disease is a genetic change 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 curved or “sickle shaped” and do not easily move through capillary vessels with small diameters, thus starving tissues from exchanging oxygen and carbon dioxide. Tissues can begin to die in severe situations. Sickle cells may lead to anemic conditions because sickle cells have a life-span of about 10–20 days, while normal red blood cells live about 120 days; thus the bone marrow may fall behind in producing 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 the symptoms of anemia:

  • Shortness of breath
  • Bone pain
  • Abdominal pain
  • Delays in puberty and growth
  • Ulcers
  • Stroke
  • Jaundice
  • Painful and prolonged erections (about 10%–40 % of men)
  • Blindness

In some individuals, the spleen becomes so impaired that it requires to be removed surgically. Removing the spleen surgically makes an individual more vulnerable to certain diseases, most notably, pneumococcal pneumonia. Sickle cell disease is fully expressed in individuals that inherit a defective hemoglobin gene from each parent.


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