Can stress cause hyperglycemia?

Yes. Glucose is an acute phase reactant, which means at times of stress, infection, "fight or flight" situations, your sugar levels may rise, at times above what's considered normal.
Yes it can. Stress can definitely cause hyperglycemia. It's a well-known phenomenon in acute illnesses in hospitals -- such as post surgery, after heart attacks, and stroke. It can dissipate as the illness remits. it can also be chronic with medication use, such as steroids in auto-immune conditions. Also in Insulin resistance w/metabolic syndrome.