General Information

Why should I donate blood?

Each year millions of Americans receive life-saving transfusions for cancer treatments, trauma treatments, organ transplants and treatment for anemia and other diseases.⁶ Blood for these transfusions comes from volunteer donors like you. Not everyone is eligible to donate but those who can donate play an important role for patients in need of transfusions. Almost two-thirds of the U.S. population is eligible to donate blood, but less than 5% of those eligible actually donate.⁷

Who can donate blood?

People of any gender, ethnicity and blood type are encouraged to donate; however, the U.S. Food and Drug Administration (FDA) sets several age, weight and health limits for donors. Generally, you must be at least 110 pounds and at least 17 years old (16 years old with a guardian's consent in some states).³ This is to ensure that the donor is physically able to give blood and remain healthy after the donation.

There are other reasons besides your age and weight why you may not be allowed to donate blood. Some of these reasons may prohibit you from donating on the particular day you try to donate and other reasons may permanently exclude you from being a blood donor. Not being allowed to give blood for one of these reasons means that you were "deferred" from donating.

Why does my blood get tested when I donate?

Before you donate, your blood will be tested for a variety of reasons. One reason is to determine if you have a high enough blood count, meaning you have enough red blood cells. This level determines if your body is healthy enough to replace the blood you give during donation. Having a low blood count is one of the most common reasons for being deferred.²

After you donate, your blood will be tested to determine your blood type and to make sure your blood is not carrying any diseases. Types of blood include positive and negative types of O, A, B and AB. Some diseases that blood is screened for include hepatitis B and C, HIV, syphilis, and West Nile virus.⁸ This process helps keep blood safe for the people receiving transfusions.

How can I prepare to donate blood?

Before you donate blood you should try to get a good night's sleep the night before, drink lots of hydrating fluids ahead of time such as milk, juice and soda, and eat healthy meals before your donation.⁹

What is it like to give blood?

The entire process of donating blood typically lasts one hour from start to finish.¹⁰ First, a medical technician will perform a pre-donation screening. He or she will ask questions about your health, lifestyle and travel history and then take your pulse, blood pressure and temperature. During this pre-screening, your blood will also be tested to determine your blood count. If you do not pass any part of this screening you may be deferred that day.

If you can donate, your blood will be drawn in about 10-15 minutes. You will be giving about one pint (450-500 mL), or 8-10% of your body's total blood.¹¹ Your body normally has an average of 10-12 pints of blood. After you are finished giving blood it is recommended that you rest, drink fluids and eat a snack. Drinks and snacks are usually provided for free to donors.

How does my body replace the blood I donated?

It takes a couple of days to replace plasma, the watery substance of your blood.¹² Making red blood cells take a little longer, but a healthy donor can replace those that were donated within two weeks. To produce these red blood cells, your body will need iron to make hemoglobin, the part of the red blood cell that carries oxygen. It is therefore very important for blood donors to have an adequate amount of iron in their diet. This is especially important for female donors, who have lower amounts of stored iron due to loss of iron in menstrual periods. Even one blood donation in a susceptible woman and three or four donations by men may exhaust the iron their bodies have stored.

Donors are eligible to donate every 56 days.¹³ However, how frequently you can donate depends upon how rapidly your body replaces the donated blood. Some donors, especially menstruating women, will not be able to donate every 56 days because they do not have enough stored iron to make new red blood cells. Iron supplements may be necessary to help raise your blood count back to a healthy level after you donate.

Blood Count Rules

The minimum hematocrit level of 38% has been set by the FDA to ensure donors have enough blood to give and that they also have enough iron available in their bodies to make more blood after they donate. Although some men with anemia (hematocrit of 38%) can donate blood, some women who do not have anemia (hematocrit of 36-37%) are not allowed to donate blood. This is because women need more than twice as much iron as men.⁵ If a nearly anemic woman (hematocrit of 36-37%) was allowed to donate, her body might not have enough iron saved up to keep her from becoming anemic. For women, saving extra iron to correct anemia can be very difficult. If your blood count indicates you have anemia, be sure to make an appointment with your physician without delay.

If I was deferred because my blood count was too low, does that mean I have anemia?

Before you are allowed to give blood, your blood count will be checked to make sure you have enough healthy blood to donate that day. A small sample is taken and tested to find the percentage of red blood cells in the sample. The medical term for this percentage is hematocrit. If your hematocrit is found to be less than 38%, you will not be allowed to donate that day.³ This minimum level has been set by the FDA to ensure donors have enough blood to give and that they also have enough iron available in their bodies to make more blood after they donate. Do not be discouraged if this happens to you because approximately 10% of all attempted donations result in a deferral because of a low blood count.¹ Other terms for low blood count are low hematocrit, low hemoglobin and low iron.

If you are deferred from donating blood because of a low blood count it is possible that you have anemia. An accurately measured hematocrit or hemoglobin level can indicate whether or not you have anemia. The normal hematocrit ranges for men and women are slightly different, and if you fall below those normal ranges you are considered anemic. Men are considered anemic when their hematocrit is below 39% and women are considered anemic when their hematocrit is below 36%.⁴ Therefore, all men who are deferred from donating blood are anemic but women who are deferred are only anemic if their hematocrit is below 36%.

If I find out I have low blood count on donation day, what do I do next?

If you are deferred from donating blood because you are told you have a low blood count, it is important to find out what may be causing it. In most cases the cause of the low blood count can be treated and then you may be able to donate again soon. There are several reasons why you may have a low blood count including iron and vitamin deficiencies, chronic illness or other invisible causes.