Chris, it doesn't take much $ to get tested for HCV exposure ... sounds like you should Definitely Check , Yes it could be very possible you were exposed ..
The odds of getting infected from using his old Interferon needles ? Who knows , usually blood is not drawn into the needle when taking Inf , but I've had several occasions where small amounts of blood entered the syringe after finishing the Interferon injection ...
Only one way to find out ... Get checked ..
Curious - HCV is the Most of my worries Contracted from my street drug daze 35 yrs ago, it's not something to be taken lightly ... now i am paying the price for those decisions in more ways than one ....
Using new needles every time would be the only safe choice , if you are going to experiment or live that lifestyle ... wish I knew this then ... !
It is not clear from your post why you and friends are injecting things together. However, if you are using street drugs, it is only a matter of time before you contract something and Hep C would be the least of your worries.
You did this before he was cleared or now after he was cleared? If you're not sure on what needle you used I would get tested right away. It is very unsafe to reuse needles you should really use a clean one every time and dispose of the old ones in a proper sharps bin. Good luck with your out come in all of this.