Why Do People Pass Out While Giving Blood?

Blood donation has several benefits for those who have serious injuries and diseases. The Mayo Clinic reports that each blood donation can help up to three people since donor centers divide whole blood into platelets, red blood cells and plasma. Because donation involves the removal of blood from the circulatory system, some people pass out while giving blood or after the blood donation process.

Some people pass out during blood donation.

Blood Donation

During the donation process, a phlebotomist or nurse inserts a needle into the vein of the donor. The collection process itself takes 8 to 10 minutes, according to the American Red Cross. Blood collection continues until 1 pint of blood has accumulated. After this procedure, the phlebotomist or nurse puts a bandage on the donor’s arm to stop any bleeding.


During the blood collection process, blood volume decreases, causing a sudden drop in blood pressure. This sudden drop causes some people to pass out while they give blood. Sudden decreases in blood sugar level also cause fainting during blood donation. "Men’s Health" magazine indicates that blood donation also has an emotional component. During emotional stress, the body directs blood flow to the muscles to prepare for the flight or fight response to danger. This diverts blood from the brain, increasing the risk that someone will pass out during the donation process.


Some people experience symptoms before they pass out. The Heart Rhythm Society defines these symptoms as presyncope. Presyncope symptoms include sweating, nausea, lightheadedness, dizziness, abdominal discomfort, headache, confusion, heart palpitations and difficulty speaking. If you experience these symptoms while donating blood, notify a donation center professional immediately.


Blood donors should take several steps to reduce the risk of passing out during the donation process. The American Red Cross recommends drinking plenty of fluids and maintaining a diet high in iron before a donation appointment. Drinking fluids will keep blood volume at normal levels, while iron consumption will counteract the loss of iron that occurs during donation. After giving blood, eat a snack that contains sugar to replace the blood sugar lost during the donation process. This will help prevent fainting after blood donation.


Some people have an increased risk for passing out because of medical conditions that affect the heart, endocrine system and nervous system. These conditions include diabetes, hypoglycemia, anxiety, irregular heartbeat, panic disorders, heart blockages and dehydration. Discuss your medical history with a physician or donation center representative to determine if blood donation is appropriate.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.
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