The reasons can be traced back to a serious medical procedure he underwent as a child. Experts also believe that James' blood is unique because after he had a lung removed at the age of 14, he was pumped with 13 units of blood.
"When I came out of the operation, or a couple days after, my father was explaining what had happened".
Blood donations saved his life, so he pledged to become a blood donor. "It's one of my talents, probably my only talent, is that I can be a blood donor".
Harrison was the program's first donor. His doctors said it was time to cease the donations - and they certainly don't take them lightly.
The Australian Red Cross Blood Service announced that Harrison made 1,100 donations in total, which went toward saving the lives of more than 2.4 million infants in need of blood transfusions. That's a risky condition that develops when a woman has rhesus-negative blood (RhD negative) and has a baby in her womb with RhD positive blood. If left untreated, the baby can suffer brain damage or die.
Soon after donating, he was found to have Rhesus-negative (Rh-) blood and Rhesus-positive (Rh+) antibodies.
If the mother has been sensitized to rhesus-positive blood, usually during a previous pregnancy with an rhesus-positive baby, she may produce antibodies that destroy the baby's "foreign" blood cells. His plasma contains an antibody (Anti-D) that can treat Rhesus D Haemolytic Disease (HDN) in unborn babies.
After turning 18, Harrison made good on his word, donating whole blood regularly with the Australian Red Cross Blood Service.
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Australian blood donor James Harrison will today make his last blood donation, having helped save the babies of more than two million Australian women. The medicine is given to mothers whose blood is at risk of attacking their unborn babies.
"And more than 17 percent of women in Australia are at risk, so James has helped save a lot of lives".
One of those lives is that of baby Samuel, who is just five weeks old.
One of the countless mothers he has helped over the decades is Joy Barnes, who works at the Red Cross Blood Bank in Sydney.
Anti-D, produced with Harrison's antibodies, prevents women with rhesus-negative blood from developing RhD antibodies during pregnancy.
"I'm grateful and I think James is really selfless to continue to donate, so that we can keep having this vaccine".
Australian scientists realized they could stop these attacks from occurring by injecting Rh-negative mothers with anti-D immunoglobulin, which basically removes the Rh-positive blood cells from the fetus in the mother's blood stream before her body can attack them.
"That's the other rare thing about James", Falkenmire told the network then.