Can I still have breast reduction?

Routine blood work for normal healthy patients before surgery can be more problematic than they are helpful. Once an abnormal value is discovered, whether it means anything or not, your surgeon will be obligated to determine that the abnormal value is either safe or treated before having surgery. Your abnormal fibrinogen result certainly could mean that you have an increased risk for a thrombotic event. It could also be a lab error or just a number that if retested could end up being normal. But now that the abnormal number has been reported, I would suggest getting clearance from a specialist. It seems as if you have already done this. At this point, I would trust the advice of the specialist and be confident that you are safe for surgery. 

Based on your description, you have already sought consultation with a ? hematologist. If this is the case, you should be able to proceed. Hopefully, your plastic surgeon will take precautions to help minimize risk of thrombosis. Best wishes.