When you have a cold, you can have some effect on your blood sugar, leading to a mild increase in blood sugar during the illness.
The body is invaded by the cold virus, which can lead to abnormal metabolic function, symptoms such as fever, and an increase in enzyme activity. These changes can mobilize the body to break down glycogen and raise blood glucose. In addition, the body can be in a state of stress and experience increased secretion of adrenaline when subjected to adverse stimuli, and these hormones, too, can lead to an increase in blood sugar levels. There are many medicines for cold and flu, such as Banlangen Punch and Paracetamol Punch, which themselves contain white sugar and other ingredients that can raise blood sugar after intake. The increase in blood sugar due to a cold is mostly secondary to mild elevation, not due to abnormal islet function, and can return to normal levels on its own after the cold is cured.
If there is a significant increase in blood glucose, you need to consider the presence of diabetes itself, and if there is a mild increase in blood glucose after the cold has subsided, you also need to consider it to be due to diabetes. You need to review your blood glucose after you recover from the cold, or have an islet function test to rule out elevated blood glucose due to diabetes.