Agree with MDs. I agree with dr malichak and dr geffner- would also add that along with elevating blood sugars as a "stress" on your body, -just having elevated blood sugars might predispose you to secondary worse infections related to a cold that does not clear as expected in 2-5 days - if sxs worsen or are not better-a diabetic should always get checked out by an md for pneumonia, or other bacterial infection..
Elevates blood sugar. Any stress - including fever may cause release of hormones that counteract Insulin and raise the blood sugar.
Common cold. No differently.