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Why Do People Faint After Giving Blood?

Donating blood is a life-saving decision. If a person gave three pints of blood a year, up to 12 people could be affected and potentially saved by one person's donations. Anybody who is between ages 17 and 60 and is in good health can donate blood. However, sometimes the process of donating blood may make donors feel light-headed or even cause them to faint. This can be a concern to some people, but is only a temporary side effect of donating blood.

  1. Blood Pressure

    • When a person donates blood, she is agreeing to have at least a pint of blood removed from her body to be used in life-saving measures for someone else. According to Dr. Deb Johnston, a physician in Brookings, South Dakota, most average-sized adults have approximately 10 pints of blood in their entire body, so when one is removed, the overall blood pressure of the individual is lowered. Low blood pressure can cause fainting.

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    Fight or Flight

    • For some donors, seeing their blood flow into bags is unnerving and can trigger the fight-or-flight reflex. This reflex moves blood into your muscles to prepare them to do what is necessary and away from the brain. Lower oxygen supply to the brain can induce fainting.

    Prepare to Donate

    • Prepare before going to give blood by making sure to drink plenty of fluids to ensure proper hydration. Also take time to eat a good meal before giving blood. Proper nutrition prior to donating blood ensures that the blood sugars are high and the donor will be less likely to feel faint.

    Relax

    • After giving blood, take some time before moving. Nurses who draw blood want donors to linger for a little while, so that they can monitor them. Move slowly when sitting up and again when finally standing. If the world begins to feel like its spinning, sit or lie back down immediately. Moving to soon after donating blood can cause a sudden drop in blood pressure and cause the donor to faint.

    Have a Snack

    • That cup of juice and cookie that is offered after donating blood isn't just a reward; it has a purpose. The body naturally starts using reserves when it has been stressed and giving blood qualifies as a stressor, so the body will look for supplies of sugar to keep moving. Having just donated a pint of blood, you can have a low blood-sugar level. The cookie and juice act quickly to restore this balance and help provide the body with the immediate rush of energy it needs.

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