Sick Day Rules for Diabetes: Insulin, Hydration, and Ketone Checks

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When you’re sick, your body isn’t just fighting a cold or the flu-it’s fighting a war with your blood sugar. For people with diabetes, illness triggers a surge in stress hormones like cortisol and adrenaline. These hormones make your body resist insulin, even if you’re not eating. Blood glucose can spike to dangerous levels-sometimes over 300 mg/dL-even when you’re too nauseous to keep food down. That’s why diabetes sick day rules aren’t optional. They’re life-saving. Many assume that if you’re not eating, you should skip your insulin. That’s one of the most dangerous myths out there. Skipping insulin during illness is the leading cause of diabetic ketoacidosis (DKA), a condition that sends over 27% of diabetes-related hospitalizations to the ER. DKA can kill. And it doesn’t just happen to Type 1 diabetics. Type 2 diabetics on insulin are just as vulnerable. Here’s what actually works when you’re sick: consistent insulin, careful hydration, and regular ketone checks. No guesswork. No skipping. No hoping it’ll pass on its own.

Never Stop Your Insulin-Even If You’re Fasting

Your body still needs insulin when you’re sick. Even if you’re vomiting or can’t eat, your liver keeps pumping out glucose. Without insulin, that glucose has nowhere to go. It builds up. Your body starts breaking down fat for energy. That’s when ketones rise. Long-acting insulin-like Lantus, Levemir, or Basaglar-must keep going. The American Diabetes Association and International Diabetes Federation both say: never reduce basal insulin below 80% of your usual dose during illness. For Type 1 diabetics, this is non-negotiable. For Type 2 diabetics on insulin, the same rule applies. If you use an insulin pump, don’t turn it off. Instead, increase your basal rate by 20% for 12 hours if your blood ketones hit 1.0 mmol/L or higher. This isn’t a suggestion-it’s a standard protocol backed by decades of clinical observation. One study in the Journal of Diabetes Science and Technology found that patients who followed this rule cut their DKA risk by over 60% during viral infections. If you’re on multiple daily injections, you still need to take your basal insulin. You may also need extra correction doses if your blood sugar stays above 240 mg/dL. Don’t wait. Give the correction. Then check again in 2-3 hours.

Hydration: The Silent Lifesaver

Dehydration makes everything worse. High blood sugar pulls water out of your cells. Vomiting or fever makes it worse. Without enough fluids, your kidneys can’t flush out ketones. That’s how DKA creeps in. The rules for hydration aren’t vague. They’re precise:

• For adults: Drink 6-8 ounces of fluid every hour. That’s about one standard glass.
• For children: Drink your age in ounces per hour (a 10-year-old drinks 10 ounces per hour).

But what kind of fluid? It depends on your blood sugar.

• If your blood sugar is below 100 mg/dL: Choose sugary fluids like regular soda, juice, or Gatorade. You need carbs to prevent low blood sugar.
• If your blood sugar is between 100-180 mg/dL: Alternate between sugar-free fluids (water, diet soda) and fluids with 15 grams of carbs (like 4 oz of juice or half a regular soda).
• If your blood sugar is above 180 mg/dL: Stick to sugar-free fluids. Water, unsweetened tea, or broth are best.

A lot of people get this wrong. They drink only water when they’re high, thinking it’ll help. But without any carbs, your body can’t use insulin properly. That’s why you need to balance fluids based on your glucose level. Keep a measuring cup nearby. Don’t guess. Pour it. Drink it hourly. Even if you’re not thirsty. Your kidneys need the flush.

Ketone Checks: When to Worry and When to Act

Ketones are your body’s emergency fuel. But too many mean you’re in danger. Test for ketones when your blood sugar hits 240 mg/dL or higher. Do it every 4-6 hours during illness. If you have a blood ketone meter, use it. Urine strips are outdated-they lag behind real-time changes. A blood ketone level above 1.0 mmol/L means you need to act. Above 1.5 mmol/L? You’re in danger zone. Here’s what to do:

• 1.0-1.5 mmol/L: Increase insulin (basal +20%, correction doses), drink fluids, and retest in 2 hours.
• 1.6-3.0 mmol/L: Call your doctor. You may need IV fluids or hospital care.
• Above 3.0 mmol/L: Go to the ER. This is a medical emergency.

Many people don’t know how to read ketone strips. A “large” reading on a urine strip is equivalent to a blood ketone level above 1.5 mmol/L. But blood meters give you real numbers. They’re worth the cost. One Reddit user, u/Type1Techie, shared: “I had the flu last winter. My ketones hit 1.8 mmol/L. I followed the +20% basal rule, drank 8 oz every hour, and retested every 2 hours. My levels dropped to 150 mg/dL in 8 hours. I avoided the ER.”

Type 1 vs. Type 2: Key Differences

Not all diabetes sick day rules are the same. For Type 1 diabetics: Ketone checks are mandatory. Insulin is non-negotiable. Even if you’re not eating, you still need insulin. Your body doesn’t produce it. You’re entirely dependent. For Type 2 diabetics: It’s more complex. If you’re on oral meds only (like metformin), you may not need ketone checks unless your blood sugar stays above 240 mg/dL for more than 12 hours. But if you’re on insulin-even once a day-you treat it like Type 1. No exceptions. Also, your blood sugar target during illness is looser. The CDC recommends keeping it between 110-180 mg/dL. That’s higher than your normal target. Why? Because pushing too hard for normal levels can cause lows, and lows during illness are dangerous.

What’s in Your Sick Day Kit?

Don’t wait until you’re sick to prepare. Build a kit now.

• Unexpired blood ketone test strips (they lose accuracy after 6 months of opening)
• Extra insulin (at least a 7-day supply)
• Insulin syringes or pens (in case your pump fails)
• Glucose tablets or juice boxes (for lows)
• Sugar-free and sugary fluids (water, diet soda, juice)
• Measuring cup (for accurate hourly intake)
• Thermometer, pain relievers (like acetaminophen-avoid ibuprofen if you have kidney issues)
• Emergency contact list: doctor, endocrinologist, pharmacy, and 24/7 ADA helpline (1-800-DIABETES)

Most people skip this step. Then they panic when they get sick. Don’t be one of them.

What to Avoid

There are traps everywhere.

• Over-the-counter cold meds: Many contain sugar, alcohol, or decongestants that raise blood sugar. Check labels. Look for “sugar-free” versions.
• Skipping insulin: Even if you’re vomiting. Even if you’re scared. Even if your doctor says “take it easy.” Your body needs insulin. Period.
• Waiting too long to test ketones: Don’t wait until you feel awful. Test when your blood sugar hits 240 mg/dL.
• Drinking only water when high: That can make insulin less effective. Balance fluids with carbs when needed.

One user on DiabetesDaily.com said: “I skipped my insulin because I was vomiting. I woke up in the ER with ketones at 22 mmol/L. I spent three days in the hospital. That was the worst week of my life.”

When to Call for Help

You don’t have to power through this alone. Call your doctor or go to the ER if:

• Your ketones are above 1.6 mmol/L and rising
• You’ve been vomiting for more than 4 hours and can’t keep fluids down
• Your blood sugar stays above 300 mg/dL for more than 6 hours, even with extra insulin
• You’re confused, breathing fast, or smell fruity (like nail polish remover)-signs of DKA
• You’ve lost 5 pounds or more in a few days

Weight loss during illness? That’s your body eating itself. It’s not normal. It’s a red flag.

What’s Changing in 2025

New tech is coming. Continuous glucose monitors (CGMs) now have alerts for rising ketones. Some pumps can auto-adjust basal rates during illness. But here’s the problem: most people don’t know how to use these features. The ADA updated its 2023 guidelines to include CGM interpretation: if more than half your readings are above 250 mg/dL for 12 hours, treat it like a high blood sugar emergency. Also, viral infections like RSV and flu cause 37% more insulin resistance than bacterial infections. That means you might need more insulin during flu season than you think. A new AI tool is in development to predict sick-day complications based on early symptoms. It’s not out yet-but it’s coming. For now, stick to the basics: insulin, fluids, ketones.

Final Reminder

Sick day rules for diabetes aren’t about perfection. They’re about prevention. You won’t always hit your target numbers. But if you follow the rules-keep insulin going, drink hourly, test ketones-you’ll avoid the ER. This isn’t theoretical. It’s survival. Every year, thousands of people end up in the hospital because they thought they could skip insulin or wait it out. You don’t have to be one of them. Start today. Make your kit. Print the rules. Stick them on your fridge. Practice the fluid rotation. Know your numbers. When you’re sick, you’re not just fighting a virus. You’re fighting your own body’s chemistry. And you’ve got the tools to win.

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• diabetes sick day rules
• insulin during illness
• ketone checks diabetes
• hydration for diabetics
• managing diabetes when sick