It think the weight limit has to do with blood volume. A person under 110lb does not have the volume to give, hence my passing out while still on the table giving. I did have a nice story to tell after the "giving" (they had to stop before they got the full amount so it got tossed). When I went to college I was told I was type O. After the donation I found I was A+ so I did have a few questions for my mother when I got home. Plus, it was the only A-plus I got while at college.
fs