Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. If you have diabetes and are ill with persistent vomiting, high blood sugar that does not respond to treatment, moderate or large ketones, or signs of dehydration, contact your healthcare provider or seek emergency care immediately.

Diabetes Sick Day Rules: Managing Blood Sugar While Ill

Last updated: March 2026 | Reviewed by MDTalks Editorial Team

Illness throws diabetes management off balance. Infections, colds, flu, stomach bugs, and other illnesses trigger the body’s stress response, releasing hormones (cortisol, adrenaline, glucagon) that raise blood sugar, even if you are eating less than usual. For people with diabetes, a routine illness can escalate into a dangerous situation if blood sugar and ketones are not managed carefully. Having a sick day plan before you get sick is essential.

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Why Illness Raises Blood Sugar

When the body fights an infection or deals with physical stress, it releases counter-regulatory hormones that increase glucose production and reduce insulin sensitivity. This happens regardless of whether you are eating normally. The result:

• Blood sugar often runs significantly higher than usual
• Insulin requirements may increase by 25% to 50% or more
• Risk of diabetic ketoacidosis (DKA) increases, especially in type 1 diabetes
• Dehydration from fever, vomiting, or diarrhea further concentrates blood sugar

Paradoxically, some illnesses (particularly gastrointestinal illness with vomiting or diarrhea) can cause hypoglycemia if food intake drops but insulin continues.

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The Core Sick Day Rules

Rule 1: Never Stop Insulin

This is the most critical rule for people with type 1 diabetes. Even if you cannot eat, your body still needs insulin. Blood sugar typically rises during illness, not falls. Stopping insulin is the most common cause of DKA during illness.

For people with type 2 diabetes on insulin, the same principle applies. Your provider may adjust the dose, but insulin should not be stopped without medical guidance.

Rule 2: Check Blood Sugar Every 2 to 4 Hours

Illness makes blood sugar unpredictable. Check more frequently than your usual schedule:

• Every 2 to 4 hours during acute illness
• Before and after any food or medication
• Through the night if blood sugar is trending high or you have ketones
• If you use a CGM, watch trend arrows closely and set tighter alert thresholds

For monitoring basics, see Blood Sugar Monitoring: How Often and When to Test.

Rule 3: Check Ketones

Ketone monitoring is essential during illness, particularly for type 1 diabetes. Check urine or blood ketones:

• When blood sugar is above 250 mg/dL
• If you are vomiting or unable to eat
• Every 4 to 6 hours during illness if ketones have been detected

Ketone Level (Blood)	Interpretation	Action
Below 0.6 mmol/L	Normal	Continue monitoring
0.6–1.5 mmol/L	Slightly elevated	Extra fluids, correction insulin, recheck in 2 hours
1.5–3.0 mmol/L	Moderately elevated	Contact your provider; likely need additional insulin
Above 3.0 mmol/L	Dangerous	Seek emergency medical care

Rule 4: Stay Hydrated

Dehydration is a major risk during illness. Aim for at least 8 ounces of fluid per hour (sip, do not gulp if nauseous):

• If blood sugar is above 250 mg/dL: Sugar-free fluids (water, broth, sugar-free electrolyte drinks)
• If blood sugar is below 250 mg/dL or you cannot eat: Alternate between sugar-free and sugar-containing fluids (regular soda, juice, electrolyte drinks) to prevent hypoglycemia

Rule 5: Adjust Medications as Directed

Your sick day plan (developed with your provider in advance) should specify:

• Insulin adjustments: Many patients need 10%–25% more basal insulin during illness. Correction doses may be needed more frequently.
• Medications to hold: Metformin is typically held during acute illness with dehydration, vomiting, or reduced kidney function. SGLT2 inhibitors should be held during illness due to euglycemic DKA risk. Discuss this with your provider in advance.
• Medications to continue: Insulin, blood pressure medications, and statins are generally continued unless your provider advises otherwise.

For medication details, see Insulin Types and Delivery Methods Compared and SGLT2 Inhibitors: How They Work for Diabetes.

Rule 6: Eat If Possible

If you can tolerate food, aim for 30 to 50 grams of carbohydrate every 3 to 4 hours. Sick day food options include:

• Saltine crackers
• Toast
• Broth-based soup
• Applesauce
• Plain rice or noodles
• Popsicles or gelatin
• Yogurt

If you cannot eat solid food, sip regular (non-diet) soda, juice, or electrolyte drinks to provide glucose.

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When to Seek Emergency Care

Go to the emergency room or call 911 if:

• Blood sugar stays above 300 mg/dL despite correction insulin
• Ketones are above 3.0 mmol/L (blood) or “large” on urine strips
• You cannot keep fluids down for more than 4 hours
• You have rapid or labored breathing
• You are confused, extremely drowsy, or cannot stay awake
• You have severe abdominal pain
• You have a fever above 101.5°F (38.6°C) that does not respond to treatment

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Create Your Sick Day Plan NOW

Do not wait until you are sick to figure out your plan. Ask your healthcare provider to help you create a written sick day plan that includes:

• When and how to adjust insulin doses
• Which medications to hold
• Ketone monitoring schedule
• When to call the provider vs. go to the ER
• Emergency contact numbers

Keep the plan posted on your refrigerator, in your phone, and shared with a trusted family member or friend.

For your provider about how to prepare for these conversations, see How to Talk to Your Doctor About Diabetes Treatment. For the comprehensive management overview, see the Complete Guide to Diabetes Management in 2026.

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Key Takeaways

• Illness raises blood sugar through stress hormones, even if you are eating less than usual.
• Never stop insulin during illness; blood sugar typically rises, not falls.
• Check blood sugar every 2 to 4 hours and ketones every 4 to 6 hours (or whenever glucose is above 250 mg/dL).
• Stay hydrated with at least 8 ounces of fluid per hour; alternate sugar-free and sugar-containing fluids based on blood sugar level.
• Hold metformin and SGLT2 inhibitors during acute illness with dehydration (per your provider’s sick day plan).
• Seek emergency care for blood sugar above 300 mg/dL that does not respond to treatment, ketones above 3.0 mmol/L, inability to keep fluids down, or signs of DKA.
• Create a written sick day plan with your healthcare provider before you need it.

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Sources

1. American Diabetes Association. “6. Glycemic Goals and Hypoglycemia / Sick Day Management: Standards of Care in Diabetes — 2026.” Diabetes Care, January 2026. diabetes.org
2. National Institute of Diabetes and Digestive and Kidney Diseases. “Managing Diabetes When You Are Sick.” niddk.nih.gov
3. Centers for Disease Control and Prevention. “Managing Diabetes: Sick Day Guidelines.” cdc.gov/diabetes

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This article is part of the MDTalks Diabetes Hub. See also AI Answers About Diabetes.

Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice. If you are ill with diabetes and have persistent vomiting, high ketones, or blood sugar above 300 mg/dL, seek immediate medical care.