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

When you’re sick, your body isn’t just fighting a cold or the flu-it’s fighting a battle that can send your blood sugar into dangerous territory. For people with diabetes, especially Type 1, getting sick isn’t just about resting and sipping tea. It’s about knowing when to adjust insulin, how much fluid to drink, and when ketones become a red flag. Many end up in the hospital not because their illness got worse, but because they didn’t know how to manage their diabetes while sick. The rules aren’t complicated, but they’re easy to ignore when you feel awful. This is what you need to do-step by step, no guesswork.

Never Stop Taking Insulin, Even If You Can’t Eat

This is the most critical rule: insulin does not take a day off when you’re sick. Your body still needs it, even if you’re not eating. When you’re ill, your liver releases extra glucose and stress hormones like cortisol and adrenaline make your body resistant to insulin. That means your blood sugar can spike-even if you’re not eating anything. Skipping insulin, even for one dose, can lead to diabetic ketoacidosis (DKA), a life-threatening condition that sends about 27% of diabetes-related hospitalizations in the U.S. each year.

For Type 1 diabetes, you must keep your long-acting insulin (like Lantus, Levemir, or Basaglar) at your usual dose. Some people think, “I didn’t eat, so I don’t need insulin.” That’s wrong. Your body is still producing glucose. For those using insulin pumps, you may need to increase your basal rate by 20% for 12 hours if ketones are moderate or large. For those on multiple daily injections, keep your basal insulin and use correction doses as needed. Type 2 diabetes patients on insulin should also keep their insulin going. Those on oral meds only might not need insulin right away-but if blood sugar stays above 240 mg/dL for more than a day, talk to your doctor. Never assume you can skip insulin because you’re not hungry.

Check Your Blood Sugar Every 2 to 4 Hours

When you’re healthy, checking your blood sugar twice a day might be enough. When you’re sick, you need to check more often. Children should check every 2 to 3 hours. Adults should check every 3 to 4 hours. Don’t wait until you feel worse. High blood sugar builds slowly. By the time you’re dizzy or nauseous, it might already be too late.

Use these thresholds as your guide:

• Below 100 mg/dL: You’re at risk for low blood sugar. Take 15 grams of fast-acting carbs.
• 100-180 mg/dL: Your sugar is in a safe zone. Keep monitoring and stay hydrated.
• Above 180 mg/dL: You need to act. Drink fluids, check ketones, and consider a correction dose.
• Above 240 mg/dL: Check ketones immediately. This is your warning sign.

If your blood sugar stays above 240 mg/dL for two checks in a row, don’t wait. Start ketone testing right away. Use a blood ketone meter if you have one. Urine strips are outdated and unreliable-they can show negative even when ketones are dangerously high. Blood ketones above 1.0 mmol/L mean you need to increase insulin. Above 1.5 mmol/L? You’re in danger zone. Call your doctor or go to urgent care.

Hydration Isn’t Optional-It’s Your Lifeline

When your blood sugar is high, your body tries to flush out the extra glucose through urine. That means you lose water fast. Dehydration makes everything worse: it raises your blood sugar even higher, makes ketones build up faster, and can lead to kidney stress or shock.

Drink fluids constantly. Adults: aim for 6 to 8 ounces every hour. Children: drink an amount equal to their age in ounces per hour (a 10-year-old drinks 10 ounces every hour). But here’s the catch-not all fluids are equal. What you drink depends on your blood sugar level.

• If your blood sugar is below 100 mg/dL: drink fluids with sugar. Regular soda, juice, or sports drinks. Avoid diet versions.
• If your blood sugar is between 100-180 mg/dL: alternate between sugar-free drinks and drinks with 15 grams of carbs. Try half water, half Gatorade. Or sip 4 oz of water, then 4 oz of juice.
• If your blood sugar is above 180 mg/dL: stick to sugar-free fluids. Water, unsweetened tea, or sugar-free electrolyte drinks like Pedialyte.

Why does this matter? If you drink sugar-free fluids when your sugar is low, you risk crashing. If you drink juice when your sugar is high, you make it worse. It’s not just about drinking-it’s about drinking the right thing at the right time. Keep a measuring cup nearby. Guessing leads to mistakes.

Ketone Checks: What They Mean and When to Panic

Ketones are your body’s backup fuel. When there’s not enough insulin, your body burns fat instead of glucose. That’s normal in fasting-but when you’re sick and insulin is low, it becomes dangerous. Too many ketones = diabetic ketoacidosis (DKA).

Test for ketones whenever your blood sugar is above 240 mg/dL. Use a blood ketone meter if you have one. Urine strips are slower and less accurate-they can miss early warning signs. Blood ketone levels:

• 0.6-1.5 mmol/L: Moderate ketones. Increase insulin and drink fluids. Recheck in 2 hours.
• 1.6-3.0 mmol/L: High ketones. Call your doctor. You may need an adjustment in insulin or fluids.
• Above 3.0 mmol/L: Emergency level. Go to the ER. Do not wait.

Don’t rely on how you feel. You can feel fine with ketones at 2.5 mmol/L. Or you can feel terrible with ketones at 0.8 mmol/L. The number tells the truth. Keep ketone strips in your sick-day kit. They expire after 6 months once opened. Check the date. An expired strip can give you a false negative-and that’s how people end up in the hospital.

Type 1 vs. Type 2: Different Rules, Same Goal

Type 1 and Type 2 diabetes handle illness differently. Type 1 patients always need insulin and always need to check ketones. Type 2 patients on insulin should follow similar rules. But if you’re on metformin or other oral meds only, you don’t need ketone checks unless your blood sugar is above 240 mg/dL for more than a day.

Here’s the key difference: Type 2 patients can sometimes manage illness without insulin-but only if their blood sugar stays under control. If it climbs past 300 mg/dL for more than 24 hours, you may need temporary insulin. Don’t wait. Call your doctor. Many Type 2 patients think, “I don’t need insulin,” and end up in DKA because they ignored the warning signs.

Also, watch your medications. Over-the-counter cold remedies often contain sugar or alcohol. A single teaspoon of cough syrup can add 10 grams of sugar. Read labels. Choose sugar-free versions. If you’re unsure, ask your pharmacist.

What to Pack in Your Sick-Day Kit

Don’t wait until you’re sick to prepare. Build a sick-day kit now. Keep it in your medicine cabinet or fridge. Include:

• Unexpired blood ketone strips (check expiration dates every 3 months)
• Glucose tablets or juice boxes (for low blood sugar)
• Sugar-free electrolyte drinks (like Pedialyte or Nuun)
• Regular soda or juice (for low blood sugar)
• A 7-day supply of insulin and other diabetes meds
• An 8-ounce measuring cup (for accurate fluid intake)
• Your doctor’s phone number and emergency contact
• A notebook to write down blood sugar, ketone, and fluid intake

Test your kit every 3 months. Replace expired strips. Check insulin expiration dates. If you use a pump, make sure you have extra infusion sets and batteries.

When to Call for Help

You don’t have to tough this out alone. Call your doctor or go to urgent care if:

• Your blood sugar stays above 240 mg/dL for more than 6 hours
• Your ketones are above 1.5 mmol/L
• You’ve been vomiting for more than 2 hours and can’t keep fluids down
• You’re confused, breathing fast, or smell fruity (signs of DKA)
• You’ve lost more than 5 pounds in a few days

These aren’t “maybe” signs. They’re emergencies. One man in Nottingham shared on a diabetes forum: “I thought vomiting meant I should skip insulin. I ended up in the ER with ketones at 8.2 mmol/L. I was lucky I didn’t lose consciousness.” Don’t be that person. Call early.

What No One Tells You

Most sick-day guides focus on numbers. But the real challenge is sticking to the plan when you’re too tired to care. You’re nauseous. Your head hurts. You just want to sleep. That’s when people skip checks. That’s when ketones rise unnoticed.

Set alarms. Every 3 hours. For blood sugar. For fluids. For ketones. Use your phone. Even if you feel fine, check. Write it down. If you can’t, ask someone to help. Parents of kids with diabetes: your job isn’t just to give insulin. It’s to be the reminder, the enforcer, the calm voice when your child is too sick to listen.

And if you use a closed-loop system? The rules are still the same. These systems don’t automatically adjust for illness. They may even shut off insulin if your sugar drops too low-which is dangerous if you’re producing ketones. You still need to override and manually increase basal rates. Talk to your diabetes team about your pump’s settings for illness. Don’t assume it knows what to do.

If you’re managing diabetes during illness, you’re not alone. Thousands do this every day. But it takes preparation, discipline, and knowing when to ask for help. Build your kit. Know your numbers. Stick to the rules-even when you feel too sick to care. Your body is fighting two battles at once. You can’t win one by losing the other.