It depends on the person. I am in the low 70's after fasting, and around 100 at night. I have been shooting up to 300 from caffeine. I've found you can't believe people who give stern yes or no answers to situations pertaining to glucose. Every person and situation is so different. It's frustrating when people give such definite answers (especially those who don't have diabetes). I am in my early 20's and have only had Type I for one month, and I am amazed at the bad advice that is out there! The only thing that is safe advice is always test when unsure. Good luck. :)
My glucose levels are very sensitive, but coffee is never an issue. I am a coffee power drinker. You can't make a blanket statement that "it will make your blood sugar rise" because that is YOUR body. No two diabetics are the same.
Caffeine can make my glucose levels rise a couple of hours later also. Not always, but often. I compensate by testing a couple of hours after my first sip of coffee and compensating with a tiny bit of insulin if glucose levels are rising. I believe that in my case, my body starts producing adrenalin when the caffeine kicks in. And adrenalin can make sugars rise. So I suspect that this effect is different for different people. Just check often while drinking coffee so you can catch it and compensate if glucose levels rise.
One more note of advice -- you cannot COUNT on this happening, so a low is very possible if you count on it like you count on eating a muffin to raise glucose levels. It really depends on what else is going on in your life at that moment, whether adrenals are stimulated and for me, whether I am drinking coffee with food or not. I have made the mistake of thinking the caffeine-induced glucose rise would happen when slightly low, only to find that it didn't happen and I ended up feeling fairly crummy while guzzling juice.
I'm not a medical professional, so take my words with a grain of salt (or caffeine), but there's no research suggesting a link. In fact, lots of recent research suggests that coffee drinkers have a reduced chance of getting type 2 diabetes (although my husband's family is full of type 2s, all of whom have been lifelong coffee drinkers, so there you go).
So the research doesn't show a link, but that doesn't mean your body can't react in a particular way. Every body is difference, and perhaps yours has an unusual reaction to coffee. Have you tried decaf and seen how your blood sugar does? Have you tried just straight black coffee, no cream or sugar? You might want to experiment a little, to see if it's the caffeine that''s the culprit, and if it is, you might want to give it up.
Good luck with the sleuthing.
Yes, coffee does and will make your BS go up. I just figure it into my morning breakfast and it works ok for me. I have to jump start myself in the mornings with coffee.