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Hemoglobin

Written by Ada’s Medical Knowledge Team

Updated on

Hemoglobin is an important protein in red blood cells that carries oxygen to the cells and that gives the blood its distinctive red color. After transporting the oxygen to the tissues that need it for their cell metabolism, hemoglobin will take carbon dioxide, a waste substance the cells produce, and transport it to the lungs so that it can leave the body.

There are a few things that can go wrong with hemoglobin that can have a serious impact on our health. It might be that there is too little hemoglobin present in the blood, which presents itself as a condition called anemia. Too much hemoglobin, on the other hand, might be caused by diseases of the bone marrow, smoking and dehydration. Apart from that, red blood cells might also be misshapen due to an inherited anomaly of hemoglobin, as seen in Sickle cell disease.[1][2]

If you think your hemoglobin levels might be out of the normal range, try using the free Ada app to find out more about your symptoms.

What is hemoglobin?

Hemoglobin is a protein that can be found in the blood and that forms part of the red blood cells. It contains iron, which gives it the possibility to transport oxygen to the tissues. Each hemoglobin molecule can bind up to four oxygen molecules to itself.[3] This way, it can transport the oxygen from the lungs to the tissues that need it. Oxygen is an important molecule to the tissues as it is crucial for the normal metabolism of the cells. This means that because of oxygen, our cells can use energy for their processes.[4] Hemoglobin is red when it is combined with oxygen, giving the blood its typical color. When hemoglobin isn’t bound to oxygen, it has a deep purple appearance.

Red blood cells containing normal hemoglobin are disk-shaped and smooth. Some conditions such as sickle cell disease can cause malformations of the red blood cells. These malformations are due to an inherited problem of hemoglobin. In sickle cell disease, the red blood cells will appear in the form of the letter C. This is problematic because the C-shaped cells are more likely to stick together and to block blood vessels.[5]

Hemoglobin is created in the bone marrow. At the end of its lifecycle, it will be broken down into iron that will be reused and bilirubin that will leave the body.[6]

Why is hemoglobin important?

Hemoglobin is a very important part of the red blood cells. It has a few functions that make it essential to the body.

  • It carries oxygen from the lungs to the tissues
  • Besides oxygen, hemoglobin can also carry carbon dioxide from the tissues to the lungs.
  • It provides the red blood cells with their color and shape.
  • Hemoglobin can bind to other substances such as sulfide, nitrogen oxide and hydrogen sulfide. This way certain drugs can bind to hemoglobin. Afterwards, hemoglobin will transport these drugs to where they should be to be effective.

What causes low hemoglobin?

Your hemoglobin levels usually depend on your age, sex and lifestyle habits. In general, the levels in newborns are the highest (14-24 g/dL). Afterwards, they decrease until the age of six, from which point they start increasing a little bit again. In grownups, there is a difference between the normal levels for males and females.

  • Adult men: 14-18 g/dL
  • Adult women: 12-16 g/dL

More information on what are considered low, high and normal hemoglobin levels can be found on our specified hemoglobin levels page.

If a blood test concludes that your values are below the normal range, it means that you have low hemoglobin. This can have various causes. In some people, low hemoglobin may be normal for a while. For example during menstruation, after donating blood or because of significant changes in altitude. However, if hemoglobin continues to be low, one of the following may be the cause:

  • Blood loss in any form. This can be caused by conditions such as hemorrhoids, ulcers or heavy menstrual bleeding.
  • The use of medications that lower your hemoglobin count, such as certain medications that lower blood pressure and chemotherapy[7][8]
  • Pregnancy
  • Fluid Retention (excess fluid buildup in the body) [9]
  • Inherited conditions such as thalassemia and malformations of hemoglobin.[10]

In test results, you might see a combination of low hemoglobin and hematocrit. Low hemoglobin refers to the amount of oxygen-carrying molecules in the blood, while hematocrit refers to the total volume of red blood cells. A decrease in hematocrit will cause a decrease in hemoglobin, as hemoglobin forms a part of the red blood cells. [11]

What are low hemoglobin symptoms?

Low levels of hemoglobin cause a condition called anemia. People with anemia may not have enough iron, vitamin B12 or vitamin B9 in the body. They may experience symptoms such as:[9][11]

  • headaches
  • tiredness
  • dizziness
  • pale skin
  • trouble breathing
  • weakness.

Who should test their hemoglobin level?

People who are experiencing symptoms of anemia should test their hemoglobin levels. It’s also recommended to have your hemoglobin levels tested if you have any family members who suffer from conditions such as thalassemia, sickle cell disease or other inheritable blood diseases.[12]

Frequently asked questions

Q: How is Hemoglobin defined? Hemoglobin is an oxygen-carrying protein that can be found in red blood cells. It contains iron and it gives the blood its red color.

Q: What does Hemoglobin do? Hemoglobin is vital to the body because it has the ability to bind to oxygen, carbon dioxide and other substances such as sulfide and nitrogen oxide. When bound to hemoglobin, these substances can get transported through the blood.

Q: When do I need to seek medical help? If you are experiencing symptoms such as fatigue, dizziness, weakness, headaches and trouble breathing, then you might have low hemoglobin and you should get your blood tested.


  1. MSD Manuals (2020). [Overview of Hemoglobinopathies](https://www.msdmanuals.com/professional/hematology-and-oncology/anemias-caused-by-hemolysis/ove rview-of-hemoglobinopathies). Accessed on 8 April 2022.

  2. National Cancer Institute (2022). PDQ Chronic Myeloproliferative Neoplasms Treatment. Accessed on 30 March 2022.

  3. Hafen BB, Sharma S. (2021). Oxygen Saturation. Accessed on 8 April 2022.

  4. Mairbäurl H, Weber RE (2012). Oxygen transport by hemoglobin. Accessed on 8 April 2022.

  5. Center for Disease Control and Prevention (2020). What is Sickle Cell Disease?. Accessed on 8 April 2022.

  6. Britannica, T. (2020). hemoglobin. Accessed on 30 March 2022.

  7. Chen TK, et.al. (2019). [Chronic Kidney Disease Diagnosis and Management: A Review] (https://pubmed.ncbi.nlm.nih.gov/31573641/). Accessed on 8 April 2022.

  8. Abdel-Razeq H, et.al. (2020). Recent update in the pathogenesis and treatment of chemotherapy and cancer induced anemia. Accessed on 8 April 2022.

  9. Hung SC. et al. (2015). Association of fluid retention with anemia and clinical outcomes among patients with chronic kidney disease. Accessed on 8 April 2022.

  10. Barrera-Reyes PK, et al (2019) Genetic variation influencing hemoglobin levels and risk for anemia across populations.*. Accessed on 11 April 2022

  11. WHO (2022). Anaemia. Accessed 30 March 2022.

  12. Sabath DE. (2017). Molecular Diagnosis of Thalassemias and Hemoglobinopathies: An ACLPS Critical Review. Accessed on 8 April 2022.

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