Sick Day Rules for Diabetes: How to Manage Insulin, Hydration, and Ketone Checks When You're Ill

When you’re sick, your body doesn’t just feel bad-it fights back in ways that can throw your diabetes completely out of balance. Even a mild cold or stomach bug can spike your blood sugar, sometimes to dangerous levels, because your body releases stress hormones like cortisol and adrenaline. These hormones make your cells resistant to insulin, meaning the insulin you take might not work as well. If you stop taking insulin because you’re not eating, or if you don’t drink enough fluids, you risk slipping into diabetic ketoacidosis (DKA)-a life-threatening condition that sends over 27% of diabetes-related hospitalizations in the U.S. each year. The good news? There’s a clear, step-by-step plan to stay safe when you’re sick. It’s not complicated, but it requires action. And it starts with three things: insulin, hydration, and ketone checks.

Never Skip Your Insulin, Even If You’re Not Eating

This is the most critical rule, and it’s the one most people get wrong. If you have Type 1 diabetes, you must keep taking your long-acting insulin-no exceptions. Even if you’re vomiting, nauseous, or haven’t eaten in 24 hours, your body still needs insulin to stop your liver from dumping glucose and to prevent ketones from building up. Skipping insulin, even for one dose, is the top reason people end up in the ER with DKA.

For Type 2 diabetes, the rule is similar if you’re on insulin. If you’re on pills only, you might not need to adjust insulin, but you still need to monitor closely. The American Diabetes Association and the International Diabetes Federation both agree: insulin should never be stopped during illness. Studies show that up to 30% of DKA cases happen because patients reduced or skipped insulin thinking they didn’t need it.

If your blood sugar is high (over 240 mg/dL), you may need to give extra correction doses. But don’t just guess. Use your usual insulin-to-carb ratio or correction factor. If you’re on an insulin pump, most guidelines recommend increasing your basal rate by 20% for 12 hours when ketones are moderate or large. For those using injections, keep your long-acting insulin on schedule and add rapid-acting insulin as needed. Keep a log: write down your doses, blood sugar, and ketone levels. It helps your doctor later.

Hydration Isn’t Optional-It’s Your Lifeline

When you’re sick, you lose fluids faster. Fever, vomiting, diarrhea, and even breathing faster than normal all drain your body’s water. But for people with diabetes, dehydration makes high blood sugar worse. It concentrates glucose in your blood and makes it harder for your kidneys to flush out ketones.

You need to drink regularly-even if you don’t feel thirsty. Adults should aim for 6 to 8 ounces of fluid every hour. For kids, the rule is simple: take their age in years and match it in ounces per hour. So a 10-year-old should drink about 10 ounces every hour.

But not all fluids are equal. What you drink depends on your blood sugar:

• If your blood sugar is under 100 mg/dL: drink fluids with sugar. Try regular soda, juice, or broth. Aim for 15 grams of carbs per serving.
• If your blood sugar is between 100 and 180 mg/dL: mix half sugary fluid with half water. For example, half Gatorade, half water. This keeps you hydrated without spiking glucose too high.
• If your blood sugar is over 180 mg/dL: stick to sugar-free fluids like water, diet soda, or broth. Avoid anything with hidden sugar-even some cough syrups.

Use a measuring cup. Don’t guess. A standard shot glass holds 1.5 ounces. A water bottle cap is about 1 ounce. If you’re vomiting, try sipping small amounts every 10 to 15 minutes. If you can’t keep fluids down for more than 4 hours, call your doctor or go to urgent care. IV fluids can be lifesaving.

Ketone Checks: What They Mean and When to Act

Ketones are acids your body makes when it burns fat for fuel instead of glucose. That sounds normal, right? But in diabetes, it’s a red flag. If your body doesn’t have enough insulin, it can’t use glucose-even if it’s floating in your blood. So it turns to fat. Too many ketones = DKA.

Test for ketones when your blood sugar is over 240 mg/dL for two checks in a row, or if you feel nauseous, have stomach pain, or are breathing fast. Use a blood ketone meter if you have one. Urine strips are outdated and unreliable-they can show low ketones even when you’re in danger.

Here’s what blood ketone numbers mean:

• Under 0.6 mmol/L: normal, no action needed
• 0.6 to 1.5 mmol/L: moderate ketones. Increase insulin, drink more fluids, check every 2 hours
• Over 1.5 mmol/L: high ketones. This is urgent. Give a correction dose of insulin, drink water, and call your doctor. If you’re on a pump, change your infusion site immediately.

Many people don’t know this: ketone strips expire. Once opened, they lose accuracy after 6 months. Keep a fresh supply in your sick-day kit. And never rely on how you feel alone. You can feel fine and still be in danger.

Type 1 vs. Type 2: Key Differences in Sick Day Rules

Not all diabetes is the same when you’re sick. Type 1 diabetes means your body makes zero insulin. That means you’re always at risk for ketones. You must test for them every time your blood sugar is high.

Type 2 diabetes is different. If you’re on oral meds only and not insulin, you might not need to check ketones unless your blood sugar stays above 240 mg/dL for more than 24 hours. But if you’re on insulin-even once a day-you treat it like Type 1. No exceptions.

Also, your blood sugar target changes when you’re sick. Normally, you might aim for 80-130 mg/dL. When ill, 110-180 mg/dL is safer. Too low can be dangerous if you’re not eating. Too high risks ketones. Don’t chase perfection. Aim for stability.

Your Sick-Day Kit: What to Pack Before You Get Sick

Don’t wait until you’re feverish to figure this out. Build your kit now. Keep it in a bag by your bed or in your medicine cabinet. Here’s what you need:

• Extra insulin (at least 7 days’ worth)
• Unexpired blood ketone strips (check expiration dates every 3 months)
• Blood glucose meter and extra test strips
• Measuring cup (8 oz) for accurate fluid tracking
• Sugar-free and sugary fluids (Gatorade, juice, broth, diet soda)
• Glucagon emergency kit (if prescribed)
• List of emergency contacts and your doctor’s number
• Over-the-counter meds without sugar or alcohol (check labels)

Many people forget about OTC meds. Cold syrups, cough drops, and even some pain relievers contain sugar or alcohol. Even a tablespoon of syrup can spike your blood sugar. Look for “sugar-free” versions. If you’re unsure, call your pharmacist.

When to Call for Help

You don’t have to figure this out alone. But you do need to know when to get help. Call your doctor or go to the ER if:

• Your blood sugar stays above 240 mg/dL for more than 24 hours, even after extra insulin
• Your ketones are over 1.5 mmol/L and don’t drop after 2 hours of fluids and insulin
• You’re vomiting for more than 4 hours and can’t keep fluids down
• You feel confused, have trouble breathing, or your breath smells fruity
• You’ve lost 5 pounds or more in a few days

Weight loss during illness is a big red flag. It means your body is breaking down muscle and fat because it’s starved for insulin. That’s not normal weight loss-it’s DKA in progress.

Real Stories, Real Lessons

One dad on Reddit shared how his 8-year-old son got the flu. He followed the “age in ounces” rule, but the boy kept vomiting. He ended up in the ER after 12 hours without fluids. The ER team gave him IV fluids and insulin. He recovered, but it was scary.

Another person, a Type 1 user, said she increased her basal rate by 20% during a cold and kept her blood sugar between 150-200 mg/dL. No ketones. No ER visit.

The difference? Preparation. Knowing the rules. Acting fast.

What’s New in 2025?

Newer tech like closed-loop insulin systems (also called artificial pancreases) are changing how people manage illness. But the rules haven’t caught up. These systems may automatically reduce insulin if your glucose drops-during illness, that’s dangerous. Right now, experts recommend manually overriding the system during sickness and sticking to manual insulin dosing.

The CDC and ADA are updating guidelines to include advice for CGM users: if more than half your readings are above 250 mg/dL for 12 hours straight, treat it like a high blood sugar emergency-even if your finger stick looks okay.

Also, new research shows 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.

Final Thoughts: It’s Not About Perfection-It’s About Action

You don’t need to be a diabetes expert to survive being sick. You just need to know the basics: keep insulin on, drink fluids, check ketones, and know when to call for help. Most people who end up in the hospital with DKA didn’t know what to do. They waited. They hoped it would get better. It didn’t.

Your body is fighting hard right now. Don’t let diabetes win because you didn’t act. Have your kit ready. Know your numbers. And remember-insulin is not optional. Hydration is not a suggestion. Ketones are not something to ignore.

This isn’t just advice. It’s a survival plan. And it works-if you use it.