Diabetes Sick-Day Rules: What to Do During Fever, Vomiting or Infection
By Dr. Moxit Shah, DM Endocrinology
Vishuddha Diabetes, Thyroid, Weight Loss Clinic, Ahmedabad
Quick answer: When you have fever, vomiting or an infection, blood sugar can rise even if you eat less. Check glucose more frequently, stay hydrated, follow a personalized medication plan and recognize emergency warning signs.
Why Blood Sugar Can Rise When You Are Sick
Fever, infections, vomiting and other illnesses trigger stress hormones that can increase glucose even when you eat less. Some people also become dehydrated or develop low glucose because they cannot eat normally. A sick-day plan helps prevent emergencies.
Check Glucose More Often
During illness, follow your clinician’s monitoring plan. People using insulin often need checks at least every 2–4 hours, depending on symptoms and readings; CGM users should confirm unexpected results with a finger-stick when appropriate. Record glucose, temperature, fluids, food and medicines.
When to Check Ketones
People with type 1 diabetes, a history of ketoacidosis or significant insulin deficiency may need blood or urine ketone testing during illness, particularly with persistent high glucose or vomiting. People taking SGLT2 inhibitors can develop ketoacidosis even without very high glucose. Seek urgent advice for positive or rising ketones, especially with nausea, abdominal pain or rapid breathing.
Do Not Stop Basal Insulin Without Medical Advice
People with type 1 diabetes must continue receiving basal insulin even when unable to eat; doses may need adjustment under their sick-day plan. People with type 2 diabetes using insulin also need individualized advice. Mealtime insulin and other drugs may need changes when food intake is reduced. Never guess doses.
Which Diabetes Tablets Might Need Temporary Review?
Dehydration, vomiting or reduced food intake may make some medicines unsafe or increase side-effect risk. Clinicians may advise temporarily withholding metformin during significant dehydration or acute kidney injury risk, SGLT2 inhibitors during serious acute illness or prolonged fasting, and certain other medicines depending on circumstances. Sulfonylureas and insulin can cause hypoglycaemia when meals are missed. Restart timing should be confirmed with your care team.
Hydration and Food During Illness
Sip fluids frequently if able to drink. Water and unsweetened fluids are generally useful, but patients with heart failure or fluid restrictions need individualized guidance. If eating normally is difficult, try small portions of tolerated carbohydrate-containing foods while following glucose monitoring advice. Oral rehydration solution may be appropriate for dehydration, but its carbohydrate content should be considered.
Treat Low Blood Glucose Promptly
If glucose is below 70 mg/dL and you are awake and able to swallow, take approximately 15 g fast-acting carbohydrate and recheck after 15 minutes. Repeat if still low. If unconscious, having a seizure or unable to swallow, do not give anything by mouth; seek emergency help and use prescribed glucagon if available.
Red Flags: When to Seek Emergency Care
Seek urgent care for persistent vomiting or inability to keep fluids down, confusion, difficulty breathing, significant ketones, severe abdominal pain, fainting, severe dehydration or very high glucose that is not improving with the prescribed plan. Diabetic ketoacidosis and hyperosmolar hyperglycaemic state can be life-threatening.
Prepare Your Personal Sick-Day Kit
Keep your glucose meter and strips or CGM supplies, ketone testing supplies if recommended, medicines and prescriptions, a thermometer, fast-acting carbohydrate, hydration supplies and emergency contact information accessible. Ask your endocrinologist for a written sick-day plan before an illness occurs.
Frequently Asked Questions
Why is my sugar high even when I am not eating?
Stress hormones released during illness can raise glucose despite reduced food intake.
Should I stop insulin during fever?
Never stop basal insulin on your own, especially in type 1 diabetes. Contact your diabetes team for individualized dosing instructions.
Can I continue an SGLT2 inhibitor while vomiting?
Significant illness and dehydration increase ketoacidosis risk. Contact your clinician promptly about temporarily withholding it and when to restart.
Can I rely only on a CGM during illness?
CGM is useful, but finger-stick confirmation may be necessary when symptoms and sensor readings disagree.
Related Diabetes Reading
Read our HbA1c guide, CGM time-in-range guide, and diabetes kidney test explainer.
Diabetes Specialist in Ahmedabad
For a personalized sick-day plan, diabetes medicine review and glucose management, consult Dr. Moxit Shah, DM Endocrinology at Vishuddha Diabetes, Thyroid, Weight Loss Clinic, 104–105, Elite Magnum, Bhuyangdev Cross Road, Ghatlodiya, Ahmedabad – 380061, Gujarat, India. Appointments: +91 99799 92797.
References and Disclaimer
- American Diabetes Association. Standards of Care in Diabetes—2026.
- Diabetes UK. Illness and diabetes: sick-day guidance.
- Joint British Diabetes Societies. Guidance on management of diabetic ketoacidosis.
This article is educational and is not an individual medicine-adjustment plan. Seek urgent medical care for signs of ketoacidosis, severe dehydration or altered consciousness.
