Does the chemo drug gemzar (gemcitabine) raise blood sugar in a diabetic?

Not known as such. Anything is possible, but this is not a common known side effect of gemzar/gemcitabine which has many side effects. You are taking this med, likely that you are on something else as well which may be the cause. Also, when ill, sugar levels tend to rise as well. Best is to consult your doc... Good luck.
No. Gemzar (gemcitabine) does not increase blood sugar. However, your doctor gave you steroids prior to chemotherapy and steroid is the one that increases your blood sugar.