Regardless of what anyone else tells you, you should use a new needle every time. Once there is blood on the end of a needle, no matter how little, there will be microbial activity on it until the next time it is used. Therefore there is a risk of infection if the same needle is used again. You may not be able to see anything on the end of the needle with the naked eye but traces of blood and microbes will be there for sure.
If someone is diabetic then they already put up with delayed healing and take longer to recover from infections. With diabetes even a small infection of the skin can possibly lead to ulceration or even gangrene in extreme cases. Trust me, I've seen (and smelled) it for myself (and it was gross)!
I too am diabetic. I am also a Science Technician who is trained in basic microbiology and I don't think it is worth the risk. It may be minimal in most cases but you only need to be unlucky once and the consequences will far outweigh the risk.
Note to johnlambert... Where did that come from? It was totally uncalled for!! How can you have the cheek to criticise the likes of Wardy and then behave like that? I didn't think the army trained you to shoot yourself in your own foot! As a military man I would expect you to behave far more gentlemanly than that to a lady. Shame on you!