An Hgb blood test measures how much hemoglobin a person has in their blood. Hemoglobin is a protein that helps red blood cells carry oxygen around the body to keep cells and organs functioning.

Hemoglobin is also what gives red blood cells their color.

If an Hgb blood test reveals that an individual’s hemoglobin is not within the normal range, a doctor may use further tests to check for possible blood disorders.

According to the National Heart, Lung, and Blood Institute, anemia — another term for low hemoglobin — is the most common blood disorder in the United States, affecting more than 3 million people.

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A doctor will use an Hgb blood test to see how much hemoglobin a person has in their blood.

An Hgb blood test involves analyzing an individual’s blood to see how much hemoglobin it contains.

The first step in the process is drawing blood. A healthcare provider, typically a nurse, will use a needle to collect the person’s blood.

They will then label the blood sample and send it off for analysis.

If the Hgb blood test reveals abnormal levels of hemoglobin, doctors may order further tests. These may include a complete blood count to provide more information about the number and type of all the cells in the blood.

A doctor may also order a hematocrit test, as this test focuses solely on red blood cells, which is where hemoglobin occurs. The hematocrit test measures what proportion of the blood the red blood cells represent.

An Hgb test can be a part of a routine checkup, or a doctor may order it if an individual is showing signs and symptoms that could be due to abnormal levels of hemoglobin.

They may order an Hgb test if a person is experiencing symptoms of anemia, for example. Anemia occurs when hemoglobin levels are low.

A doctor may also ask for an Hgb test to ensure that the treatment for abnormal hemoglobin levels is effective.

If a person’s hemoglobin levels are higher or lower than the figures below, they may have a medical condition.

The medical community typically defines the normal ranges of hemoglobin as follows:

  • Children: 11–16 grams per deciliter (g/dl)
  • Females: 12–15 g/dl
  • Males: 13.5–18 g/dl
  • Pregnant women: Usually higher than 10 g/dl

The typical percentage of red blood cells in the blood ranges from 37% to 49%.

Some factors can affect the results of an Hgb test. These include:

  • medications
  • a person’s menstrual cycle
  • lifestyle choices, such as diet and exercise
  • a recent blood transfusion

Learn more about hemoglobin levels here.

When a person has high levels of hemoglobin, doctors refer to this as polycythemia.

Symptoms

The symptoms of polycythemia include:

  • headaches
  • tiredness
  • shortness of breath
  • enlarged spleen

A person may also experience pruritis, or itching, on the back after a warm shower.

Causes

Factors that can cause high levels of hemoglobin include:

  • living at a high altitude
  • smoking
  • dehydration
  • lung disease
  • liver disease
  • congenital disabilities in the heart that interfere with oxygenated blood
  • chronic obstructive pulmonary disease (COPD)
  • extremely intense exercise
  • polycythemia vera, a rare disease that causes the body to produce too many red blood cells

Anemia is another term for low hemoglobin.

Symptoms

The symptoms of anemia include:

Causes

Possible causes of a low hemoglobin reading in an Hgb blood test include:

  • significant loss of blood as a result of trauma, surgery, or ongoing internal bleeding
  • ulcers
  • heavy periods
  • bone marrow problems, due to cancers such as leukemia
  • cancers such as colon cancer, which can cause internal bleeding, and lymphoma, which damages the bone marrow
  • kidney failure, which interferes with the production of hemoglobin
  • Crohn’s disease and ulcerative colitis
  • thalassemia, which occurs when the body is unable to produce enough hemoglobin
  • sickle cell anemia
  • chronic inflammation
  • a diet deficient in iron, vitamin B-12, and folate

An Hgb blood test can provide important information about an individual’s health.

The person’s outlook depends on whether their hemoglobin is high, low, or normal and on what is causing any irregularities that the test has revealed.

Routine blood tests can sometimes reveal serious health problems before symptoms develop and make early, lifesaving intervention possible.

An Hgb blood test is a routine medical procedure that doctors sometimes include as part of a regular physical examination.

The test measures how much hemoglobin is in an individual’s blood, and it is a very important health indicator.

Many different factors can lead to abnormal Hgb readings, and the treatment will depend on the cause.