2. Check blood glucose often.

When a person is sick, his body is under stress. To deal with it, his body releases hormones that help fight disease. These can also elevate blood sugar levels and interfere with the effects of insulin, which lowers blood sugar.

This makes it harder for him to keep his blood sugar in his target range during an illness. That's why he needs to check his blood sugar more often so he can keep close tabs on his glucose numbers. His doctor or diabetes educator may recommend measuring blood sugar at least four times a day, every few hours, or at some other interval. Find out in advance, before an illness occurs, how often his healthcare team advises testing. If he's too sick to test himself, you or another caregiver can perform this task.

3. Test urine ketones.

Illness can trigger a buildup of ketones -- acids produced by the body when there's a shortage of insulin -- in the urine. High levels of ketones can lead to two potentially life-threatening ailments: diabetic ketoacidosis and hyperosmolar hyperglycemic nonketotic syndrome.

A simple home urine test will alert you to possibly high levels of ketones in a patient's urine. His diabetes doctor may advise measuring ketones if his blood sugar level is higher than 300 milligrams/per deciliter (mg/dL), or she may recommend routine testing during sick days.