Pathology Laboratory (Medical)

What is Hemoglobin? High and Low Hemoglobin

Last updated on October 20th, 2022 at 08:01 am

What is hemoglobin?

Hemoglobin is a protein found in red blood cells. It gives blood its red colour, and its job is to carry oxygen throughout your body.


The hemoglobin (Hb) test measures how much hemoglobin your red blood cells contain. Hb is a protein produced by your bone marrow that’s stored in red blood cells. It helps red blood cells transport oxygen from your lungs to your body through your arteries. It also transports carbon dioxide (CO2) from around your body back to your lungs through your veins. Hb makes red blood cells look red.

Abnormally high or low hemoglobin (Hb) can cause symptoms like exhaustion, dizziness, or shortness of breath. Your doctor may suggest a Hb test if you’re experiencing these symptoms. You may have an underlying condition that needs to be diagnosed.

Why do I test hemoglobin?

The Hb test may be prescribed as part of a complete blood count (CBC) test. A CBC test also measures other important components of your blood, such as white blood cells and platelets. Abnormal levels of these cells can show underlying conditions or blood disorders.

Here are a few other reasons your doctor may advise a Hb test; you don’t need to fast for the Hgb test specifically.

  • You have parents or other family members who have blood disorders, such as sickle cell anaemia.
  • You have an infection.
  • You don’t have enough iron in your diet.
  • You’ve lost a lot of blood after surgery or a traumatic injury.
  • You are pregnant.
  • You have a medical condition that can affect your Hb levels.

Hemoglobin Normal Ranges


11–18 g/dL

Young children

11.5–16.5 g/dL

Adult males

13–16.50 g/dL

Adult females (non-pregnant)

12–16 g/dL

Adult females (pregnant)

11–16 g/dL

Symptoms of low hemoglobin

Low Hb is also known as anaemia, so you don’t have enough red blood cells in your body. With anaemia, a blood test will also show that you have a low red blood cell count and may have low hematocrit, the volume of red blood cells, to other components in your blood.

Anaemia can have many causes, so symptoms can vary widely. Common anaemia symptoms can include:

  • exhaustion
  • skin paleness
  • shortness of breath
  • abnormal or rapid heartbeat
  • pain in your chest
  • cold, swollen hands or feet
  • a headache
  • the trouble with physical activity

Causes of low hemoglobin

Probable causes of low Hb include;

  • lack of iron in your diet, which makes it harder for your bone marrow to produce Hb
  • lack of Folic Acid or vitamin B-12, which can lead to your body produces fewer red blood cells that are needed
  • severe blood loss after surgery or a major injury
  • internal bleeding from stomach ulcers, stomach or colon cancer, or internal injuries
  • sickle cell anaemia, a genetic condition that causes red blood cells to be abnormally sickle-shaped and able to carry less Hb
  • hypothyroidism, so the thyroid gland doesn’t produce enough thyroid hormones
  • splenomegaly, or an enlarged spleen from infection, liver conditions, or cancer
  • bone marrow conditions, such as leukaemia, that prevent your bone marrow from producing enough red blood cells
  • chronic kidney disease, in which your kidneys don’t function properly (resulting in a deficiency of erythropoietin, a hormone that stimulates red blood cell production in your bone marrow)

Symptoms of high hemoglobin

High Hb is known as polycythemia. This means you have too many red blood cells. Polycythemia vera is a cancer of the blood in which your bone marrow overproduces red blood cells. With polycythemia, a blood test also shows that you have a high red blood cell count and high hematocrit.

Common symptoms of high Hb levels include;

  • itchiness
  • a headache
  • dizziness
  • getting easily bruised or bleeding
  • sweating more than usual
  • painful joint swelling
  • abnormal weight loss
  • yellow tint to the eyes and skin (jaundice)
  • feeling exhausted
  • purple or reddish tint to the skin

Causes of high hemoglobin

Probable causes of these types of high Hb levels include;

  • living at high altitudes where there’s not as much oxygen in the air, such as in the mountains
  • smoking tobacco products, including cigarettes or cigars
  • chronic obstructive pulmonary disease (COPD), a condition that inflames the lungs and blocks air from getting into your lungs
  • heart or lung diseases that affect your ability to breathe, your lungs’ ability to pass oxygen into your bloodstream, or your heart’s ability to pump normally
  • taking erythropoietin unnecessarily, such as to enhance high-level physical performance

Also Read: Appendix | Thrombophilia

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