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

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 simple cold or stomach bug can spike your blood sugar, push you toward dangerous ketones, and make you feel worse than the illness itself. For people with diabetes, especially Type 1, being sick isn’t just about resting and drinking tea. It’s about following clear, life-saving steps: keeping insulin going, staying hydrated, and checking ketones regularly. Skip any one of these, and you could end up in the hospital with diabetic ketoacidosis (DKA)-a condition that sends over 27% of diabetes-related emergency visits to the ER, according to CDC data from 2022.

Never Stop Insulin, Even If You Can’t Eat

One of the biggest mistakes people make when they’re sick is skipping their insulin because they’re not eating. That’s dangerous. When you’re ill, your body releases stress hormones like cortisol and adrenaline. These hormones tell your liver to pump out more glucose-even if you haven’t eaten a thing. At the same time, your body becomes more resistant to insulin. The result? Blood sugar can jump 30-50% higher than normal, sometimes within hours.

Long-acting insulin (like Lantus, Levemir, or Basaglar) is your anchor during illness. You must keep taking it, even if you’re vomiting or eating nothing. The American Diabetes Association and International Diabetes Federation both say: never reduce basal insulin below 80% of your usual dose. For Type 1 users, going even lower can trigger ketone buildup fast. For Type 2 users on insulin, the same rule applies-your body still needs insulin to fight the stress of infection.

If you use an insulin pump, you might need to increase your basal rate by 20% for 12 hours if ketones are moderate or large (blood ketones ≥1.0 mmol/L). That’s not a guess-it’s a standard protocol backed by clinics like Cleveland Clinic and Archildrens.org. Multiple daily injection users should follow the same rule: keep your long-acting dose, and use correction doses for high blood sugar as you normally would. Don’t wait for it to get worse. Act early.

Hydration Is Your Lifeline

Dehydration makes everything worse. High blood sugar pulls water out of your cells, and vomiting or fever makes it worse. Without enough fluids, your blood thickens, your kidneys struggle to flush out ketones, and your risk of DKA climbs. That’s why hydration isn’t optional-it’s the first line of defense.

Adults should aim for 6-8 ounces of fluid every hour. For children, the rule is simple: age in ounces per hour. A 10-year-old needs 10 ounces every hour. That’s about three standard cups of water, broth, or sugar-free drinks. But here’s the catch: not all fluids are equal.

If your blood sugar is above 180 mg/dL, stick to sugar-free fluids: water, unsweetened tea, or diet soda. If it’s between 100-180 mg/dL, alternate between sugar-free fluids and drinks with 15 grams of carbs-like half a cup of regular Gatorade or 4 oz of apple juice. This keeps you hydrated without spiking your sugar. If your blood sugar drops below 100 mg/dL, switch to sugary fluids to prevent lows. The key is rotation. Don’t just chug water all day if you’re not getting carbs. And don’t drink sugary drinks unless your blood sugar needs them.

Many people struggle with this during vomiting or nausea. If you can’t keep fluids down for more than four hours, call your doctor or go to the ER. IV fluids are often needed to reset your system. Don’t wait until you’re dizzy or confused. Early intervention saves lives.

Ketone Checks: What They Mean and When to Act

Ketones are your body’s emergency fuel. When it can’t use glucose because of insulin shortage, it starts burning fat instead. That’s normal in fasting-but during illness, it’s a red flag. Too many ketones mean you’re heading toward diabetic ketoacidosis.

Check ketones whenever your blood sugar is above 240 mg/dL. Some guidelines say to check after two consecutive readings over 300 mg/dL. Either way, don’t wait. Use a blood ketone meter if you have one-it’s more accurate than urine strips. Urine strips can be misleading because they show ketones from hours ago, not what’s happening right now.

Here’s what the numbers mean:

• Below 0.6 mmol/L: Normal. Keep monitoring.
• 0.6-1.5 mmol/L: Mild ketones. Increase fluids, check every 2 hours, and give a correction dose if needed.
• 1.5-3.0 mmol/L: Moderate ketones. Increase basal insulin by 20% for 12 hours. Call your care team if it doesn’t drop in 4 hours.
• Above 3.0 mmol/L: High ketones. This is an emergency. Go to the ER or call 999. Don’t delay.

People with Type 1 diabetes must check ketones during every illness. Type 2 users on insulin should too. Those on pills only don’t usually need to check unless blood sugar stays above 240 mg/dL for more than 12 hours. But if you’re unsure, test anyway. Better safe than sorry.

What to Do If You’re Vomiting or Can’t Eat

Nausea and vomiting are common during illness-and they’re a nightmare for diabetes management. You can’t eat, you can’t drink, and your blood sugar keeps rising. This is when people panic and stop insulin. Don’t.

Even if you can’t keep food down, you still need insulin. Try small sips of fluids every 15 minutes. Use the 15-gram carb rule: if your sugar is between 100-180 mg/dL, take 15 grams of carbs every hour-like 4 oz of apple juice or 1/2 cup of regular soda. If you can’t keep even that down, you need medical help. IV fluids and insulin are often given in the hospital to stabilize you.

Also, don’t rely on over-the-counter cold medicines without checking the label. Many contain sugar, alcohol, or decongestants that can spike blood sugar or mask symptoms. Look for sugar-free versions. If you’re unsure, call your pharmacist.

Prepare a Sick Day Kit Before You Get Sick

Waiting until you’re sick to figure out what you need is risky. Build a sick day kit now. Here’s what to keep on hand:

• Unexpired blood ketone strips (they last 6 months after opening)
• Extra insulin (at least a 7-day supply)
• Glucose tablets or juice boxes (for lows)
• Sugar-free electrolyte drinks (like Pedialyte or sugar-free Gatorade)
• A measuring cup (so you can track 6-8 oz accurately)
• Logbook or app to track blood sugar, ketones, fluids, and insulin doses
• Emergency contact numbers: your doctor, endocrinologist, and the ADA helpline (1-800-DIABETES)

Store this kit where you can find it fast-next to your insulin, not buried in a cabinet. Check expiration dates every 3 months. Expired ketone strips can give false negatives, and the FDA warns that 18% of home tests using old strips miss dangerous ketone levels.

When to Call for Help

You don’t have to handle this alone. But you need to know when to ask for help. Call your doctor or go to the ER if:

• Your ketones are above 1.5 mmol/L and not dropping after 4 hours of fluids and insulin
• 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 despite corrections
• You feel confused, have trouble breathing, or smell fruity on your breath (a sign of ketones)
• You’ve lost more than 5 pounds in a few days without trying

These aren’t just warnings-they’re red flags. In 2022, the CDC reported that 2-5% of DKA cases end in death. Most of those cases happened because people waited too long to get help.

What’s New in 2026: CGMs and AI

Technology is helping. If you use a continuous glucose monitor (CGM), pay attention to trends. If more than half your readings are over 250 mg/dL for 12 hours straight, treat it like a ketone warning-even if your fingerstick isn’t that high yet. New guidelines from the ADA in 2023 now include CGM patterns as part of sick day protocols.

There’s also emerging tech on the horizon. The NIH is funding AI tools that predict when illness will trigger a blood sugar spike based on early symptoms like fatigue or slight fever. These tools, expected in late 2025, could send alerts before ketones even form. But for now, the old rules still save lives: insulin, fluids, ketones.

Real Stories, Real Risks

One Reddit user, u/SickDayStruggles, said different doctors gave conflicting advice: one told them to skip insulin when vomiting, another said never stop it. They ended up in DKA with ketones at 22 mmol/L. That’s a life-threatening level.

Another, u/Type1Techie, followed the +20% basal rate rule during the flu. Their blood sugar stayed between 150-200 mg/dL. No hospital visit. No DKA.

The difference? Knowledge and action. You don’t need to be a doctor. You just need to know the rules and stick to them.