Tattoo and blood help?

I've been wanting to get a tattoo to commemorate a certain special event in my life, but people around me have told me that getting a tattoo negativity affects the ability to give blood. I do give blood and although I am only 19, I really feel that I'm making a difference by doing so. Getting a tattoo is important to me, but not at the risk of not being able to give blood. So I guess my question is, does getting a tattoo really mean I cannot freely give blood? How does it affect the quality of my blood or what is the cause of the concern of getting tattoos and giving blood? Or was this just a made up thing to prevent me from getting a tattoo...