Why is my hemoglobin and/or hematocrit checked before giving blood?

American Red Cross
Hematocrit and hemoglobin measurements are blood tests. Hemoglobin enables red cells to transport oxygen and carbon dioxide. The hemoglobin is checked before each donation to 
ensure that the donor has adequate red blood cell levels to donate blood. Blood donors must have a minimum of 12.5 g/dL hemoglobin or a hematocrit of 38% to be accepted for donation. The hematocrit is a measure of the volume that red blood cells take up in the blood. Most men have a hemoglobin of 12.5 g/dL or greater and a hematocrit above 38 percent, but many women naturally have lower hemoglobin/hematocrit levels. An abnormally low hemoglobin/hematocrit, which indicates anemia, can develop when a person either does not make enough red blood cells, loses blood from the body, or is iron-deficient. The most common cause of mild anemia is a low level of iron, which is needed to make red blood cells. Frequent blood donations and monthly blood loss in premenopausal women can contribute to a low iron level.
Most hemoglobin/hematocrit readings that are lower than the required level do not indicate the donor has serious health issues. Some donors naturally have lower levels, which causes them no harm. However, it does prevent them from being eligible blood donors. Other donors may be slightly anemic due to iron deficiency, and increasing their iron intake may boost their hemoglobin/hematocrit level. Donors who are temporarily deferred are given information to help them determine if they are eligible to give blood again in the coming months. The Red Cross encourages all donors who are temporarily deferred to try to give blood again if it is safe for them to do so.

Continue Learning about Blood Basics

Blood Basics

Blood Basics

Our blood is a living tissue with a variety of critical functions: It delivers oxygen and nutrients to our organs, fights infections and creates blood clots, preventing us from bleeding excessively when a blood vessel is damaged. ...

The liquid part of our blood, called plasma, is key for maintaining blood pressure and supplying critical proteins for blood clotting, immunity and maintaining the correct pH balance in our body -- critical to cell function. Plasma also carries the solid part of our blood -- white blood cells, which work to destroy viruses and bacteria; red blood cells, which carry oxygen through the body; and platelets, which help clotting. Learn more about blood basics with expert advice from Sharecare.

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.