Hemoglobin is an iron-rich protein in red blood cells. It gives blood its red colour.  

Hemoglobin transports oxygen to and removes carbon dioxide from our organs and tissues. The hemoglobin molecule contains iron, an essential mineral found in our diet.   

When you donate blood, you’re also donating some of your hemoglobin. That’s why it’s important for donors to consider their iron health.  

Low hemoglobin, also called anemia, can lead to tiredness, difficulty breathing, difficulty concentrating and lightheadedness.  

Hemoglobin FAQs

What are normal hemoglobin levels?

Normal hemoglobin levels differ depending on several factors, including sex at birth, as well as hormonal supplementation.  

Normal hemoglobin levels can range from 120 g/L to 180 g/L. 

We test each donor’s hemoglobin before they donate and require a minimum hemoglobin (hgb) of 125 g/L for donors registered as female and 130g/L for donors registered as male. 

Why does Canadian Blood Services measure hemoglobin levels?

We measure hemoglobin to protect you as a donor. It is important that you do not donate blood if your hemoglobin level is low.  

Donating blood leads to a decrease in hemoglobin. Low hemoglobin, or anemia, can cause tiredness, lightheadedness, difficulty breathing and/or difficulty concentrating.  

How is hemoglobin measured?

We check each donor’s hemoglobin level at the clinic before every donation with an onsite finger stick test. This is a point-of-care capillary blood hemoglobin test, which is different from a venous blood test that would be ordered by a healthcare practitioner for diagnostic purposes.  

What does it mean to have low hemoglobin?

The most common reason for low hemoglobin is due to low iron stores. Iron is needed to make red blood cells. Low iron stores can lead to fatigue, difficulty concentrating and decreased exercise capacity. 

Causes of low iron stores include:  

  • Not enough iron in your diet 

  • Blood donation  

  • Menstrual blood loss 

  • Iron not being absorbed by the digestive tract, as seen in celiac disease  

  • Rarely, gradual bleeding from the digestive tract, such as from the colon. 

What is anemia?

Anemia is the medical term for when an individual has low hemoglobin. Anemia can lead to symptoms such as fatigue, difficulty breathing, lowered exercise tolerance, lightheadedness and difficulty concentrating.  

If you have anemia, you should not return to donate until the cause of anemia has been treated and hemoglobin improves. 

How can donating blood become a potential cause of anemia (low hemoglobin)?

Frequent blood donation can contribute to anemia because each whole blood donation results in a drop of hemoglobin levels by approximately 10 g/L and reduces the body’s iron stores.

Healthy donors produce new red blood cells to replace donated cells. Iron is essential to the production of new red blood cells. If your iron levels become too low, your body may have more difficulty replenishing your red blood cells. 

How can I prevent anemia due to blood donation?

Donors need to have an adequate amount of iron. All donors should consider iron supplements to help replenish the iron lost in donations. 

What can I do if I have low hemoglobin (anemia)?

We recommend that you see your doctor to check your hemoglobin levels and iron stores (ferritin). Your doctor will investigate reasons why your hemoglobin is low and may suggest taking iron pills.  

All blood donors should eat an iron-rich diet and consider iron supplementation. 

When can I come back to donate?

Being deferred for low hemoglobin protects your own health. Most people who have low hemoglobin (anemia) are able to increase their hemoglobin and become donors again, provided they meet all other eligibility criteria.

It can take four to six months to rebuild your iron stores. Seek professional medical advice to help you determine when to donate again.  If your healthcare practitioner has started you on iron pills, you may return to donate six months after starting them if your hemoglobin and iron levels are back to normal. Once your iron is back to normal, and if you plan to donate regularly, speak to your doctor or pharmacist about taking iron supplementation to prevent low iron. 

Consider limiting how often you donate blood to two to three times a year. 

Can a person’s iron level be too high?

Yes. Hemochromatosis is an inherited genetic disorder where too much iron is absorbed from the diet. Eventually, the excess iron accumulates in tissues, such as the liver, pancreas and heart. Without treatment, excessive levels of iron can be toxic.

Learn more about hemochromatosis.

Can a person’s hemoglobin level be too high?

Yes. High hemoglobin, also called polycythemia, can occur for many reasons. Some causes of high hemoglobin (polycythemia) include smoking, testosterone supplementation, lung problems, kidney problems and problems in how the bone marrow makes blood (polycythemia rubra vera or myeloproliferative neoplasms).

Some conditions causing high hemoglobin are a cause for donor deferral, either for donor safety or recipient safety. Therefore, in many instances, additional information may be required from the donor’s healthcare practitioner to determine eligibility.

I am a healthy female donor, but I seem to fail my hemoglobin test every second time. What steps can I take to improve my hemoglobin levels?

We understand that this can be frustrating. Here are some things you could do:

  • Try to increase your dietary iron intake.
  • Reduce your blood donation frequency.
  • Speak to your healthcare practitioner about the need for iron supplementation.