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

When you’re sick with a cold, flu, or stomach bug, your body isn’t just fighting off germs-it’s also throwing your blood sugar into chaos. For people with diabetes, especially Type 1, being sick isn’t just about resting and drinking tea. It’s a medical event that can quickly turn dangerous if you don’t know what to do. The rules are simple, but they’re not optional: insulin must keep going, fluids must be tracked, and ketones must be checked. Skip any one of these, and you risk diabetic ketoacidosis (DKA)-a life-threatening condition that sends thousands to the ER every year.

Why Illness Makes Diabetes Harder

When you’re sick, your body releases stress hormones like cortisol and adrenaline. These are meant to help you fight infection, but they also make your liver pump out extra glucose. At the same time, your cells become more resistant to insulin. The result? Blood sugar can spike 30-50% higher than normal-even if you’re not eating. This isn’t just inconvenient. It’s dangerous. High blood sugar without enough insulin causes your body to break down fat for energy, producing ketones. Too many ketones = acid buildup = DKA.

According to CDC data from 2022, nearly 27% of all diabetes-related hospitalizations are due to DKA triggered by illness. And the worst part? Many of these cases happen because people stop taking insulin when they’re sick. They think, “I’m not eating, so I don’t need insulin.” That’s a deadly mistake. Even when you’re vomiting or fasting, your body still needs basal insulin to keep ketones from rising.

Never Stop Long-Acting Insulin

This is the most important rule: never stop your long-acting insulin (Lantus, Levemir, Basaglar) just because you’re not eating. Your body still needs it. Basal insulin isn’t about food-it’s about keeping your liver from dumping glucose and preventing ketone production.

For Type 1 diabetes, your basal rate should never drop below 80% of your usual dose during illness, even if your blood sugar is low. For Type 2 diabetes, you might not normally use insulin, but if you’re sick and your blood sugar stays above 240 mg/dL for more than a few hours, you may need to start short-acting insulin temporarily. Don’t wait for your doctor to tell you-have a plan ready.

Insulin pump users face a slightly different challenge. If your ketones are moderate or large (blood ketones ≥1.0 mmol/L), you need to increase your basal rate by 20% for at least 12 hours. You still need to give correction doses for high blood sugar. Don’t turn off your pump or delay boluses. If you’re unsure, call your diabetes care team. Waiting can cost you hours-or your health.

Hydration: Drink Like Your Life Depends on It (Because It Does)

Dehydration makes everything worse. High blood sugar pulls water out of your cells. Vomiting and fever make it worse. Without enough fluids, your kidneys can’t flush out ketones and excess glucose. That’s how DKA starts.

Here’s what to drink:

• If your blood sugar is above 180 mg/dL: Stick to sugar-free fluids. Water, unsweetened tea, or electrolyte drinks without sugar (like Zero Sugar Gatorade or Pedialyte).
• If your blood sugar is between 100-180 mg/dL: Alternate between sugar-free fluids and fluids with 15 grams of carbs per 8 oz. That’s half a cup of regular soda, half a cup of juice, or a small sports drink. This keeps you hydrated without spiking your sugar too high.
• If your blood sugar is below 100 mg/dL: Drink fluids with carbs. 4-8 oz of regular soda, juice, or even broth with a little salt can help prevent low blood sugar while keeping you hydrated.

Adults should aim for 6-8 ounces of fluid every hour. For kids, use the “age in ounces” rule: a 10-year-old should drink 10 ounces per hour. Use a measuring cup. Don’t guess. If you’re vomiting, try sipping small amounts every 10-15 minutes. If you can’t keep anything down for more than 4 hours, go to the ER. IV fluids are faster and safer than trying to force it down.

Ketone Checks: When and How to Test

Ketone testing isn’t optional when you’re sick. You need to know if your body is burning fat for fuel. There are two ways to check: urine strips or blood ketone meters. Blood ketone meters are more accurate and faster. Urine strips can be misleading-they show ketones from hours ago, not what’s happening now.

Test your ketones when:

• Your blood sugar is over 240 mg/dL for two checks in a row
• You feel nauseous, vomit, or have stomach pain
• You’re feeling unusually tired or confused

Interpretation is key:

• Below 0.6 mmol/L: Normal. Keep monitoring.
• 0.6-1.5 mmol/L: Moderate ketones. Increase insulin (if on pump, +20% basal), drink fluids, retest in 2 hours.
• Over 1.5 mmol/L: High ketones. Take immediate action. Give a correction dose of insulin, drink fluids, and call your doctor. If you’re on a pump, change your infusion site right away. A clogged site can cause ketones to spike even if you’re giving insulin.

Many people use urine strips because they’re cheaper. But if your urine says “large” ketones, treat it like blood ketones over 1.5 mmol/L. Don’t wait. Don’t hope it gets better. Act.

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

Type 1 and Type 2 diabetes handle sick days differently, but both need vigilance.

For Type 1: You’re always at risk for DKA. Ketone checks are mandatory. You must keep insulin on, even if you’re not eating. Your body can’t make insulin, so you’re completely dependent on what you inject.

For Type 2: If you’re on insulin, treat yourself like a Type 1. Check ketones, don’t skip insulin. If you’re only on pills like metformin or GLP-1s, you’re less likely to develop DKA-but not immune. If your blood sugar stays above 240 mg/dL for more than 12 hours, check ketones anyway. Some Type 2 patients develop ketones during severe illness, especially if they’re dehydrated or have an infection.

Also, some Type 2 patients are prescribed SGLT2 inhibitors (like Jardiance or Farxiga). These drugs can increase ketone risk even with normal blood sugar. If you’re on one of these, your doctor should have given you specific sick day instructions. If not, call them before you get sick. Don’t wait for an emergency.

What to Keep in Your Sick Day Kit

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

• Unexpired blood ketone test strips (they last 6 months after opening)
• Extra insulin (at least 7 days’ supply)
• Glucagon emergency kit (if you’re on insulin)
• Measuring cup (for accurate fluid intake)
• Sugar-free and sugary fluids (Gatorade, juice, broth)
• Easy-to-eat carbs: crackers, applesauce, gelatin
• Thermometer, logbook, or app to track blood sugar and ketones

Check your kit every 3 months. Expired strips give false negatives. That’s how people end up in the ER thinking they’re fine-until they’re not.

When to Call for Help

You don’t have to figure this out alone. But you do need to know when to call. Get help if:

• Your blood sugar stays above 240 mg/dL for more than 6 hours despite extra insulin
• Your ketones are over 1.5 mmol/L and rising
• You’re vomiting and can’t keep fluids down for more than 4 hours
• You’re confused, breathing fast, or smell fruity (like nail polish remover)
• You’ve lost more than 5 pounds in a few days

These are red flags. Don’t wait. Call your doctor. Go to urgent care. If you’re alone, call 911. DKA doesn’t wait for appointments.

Common Mistakes (And How to Avoid Them)

People make the same mistakes over and over:

• Skipping insulin: “I’m not eating, so I don’t need it.” Wrong. Basal insulin isn’t for food-it’s for survival.
• Using urine strips instead of blood meters: Urine ketones are outdated. Blood ketones tell you what’s happening now.
• Drinking too much sugary drink: Trying to “treat” high blood sugar with juice makes it worse. Stick to the carb rules.
• Ignoring OTC meds: Cold medicines often have sugar or alcohol. Check labels. Use sugar-free versions.
• Waiting to act: “I’ll check again tomorrow.” DKA doesn’t wait. Act fast.

One Reddit user, u/SickDayStruggles, shared: “Different doctors told me to skip insulin when vomiting versus never skip it. I ended up in DKA with ketones at 22 mmol/L.” That’s the cost of confusion. Don’t be that person. Have a written plan from your diabetes team. Stick to it.

What’s New in 2026

Guidelines are evolving. In 2023, the ADA updated its sick day rules to include guidance for people using continuous glucose monitors (CGMs). If more than half your readings are above 250 mg/dL for 12 hours, treat it like a high blood sugar emergency-even if your finger stick says it’s okay. CGMs can lag, but trends matter.

Also, viral illnesses like RSV and flu cause 37% more insulin resistance than bacterial infections. That means you might need more insulin than usual during flu season. Be ready.

Future tools are coming. In 2025, AI-powered apps will predict when you’re likely to get sick based on early symptoms and suggest insulin adjustments before your blood sugar spikes. But for now, the old rules still save lives: insulin on, fluids in, ketones checked.

Next Steps: Build Your Plan Today

Don’t wait until you’re sick to learn this. Sit down with your diabetes care team and write out your personal sick day plan. Include:

• Your usual insulin doses
• When to increase insulin
• How to hydrate based on your blood sugar
• When to test ketones and what to do with results
• Emergency contacts and when to call for help

Keep it in your phone, your wallet, and your sick day kit. If you’re a parent of a child with diabetes, share this plan with teachers, babysitters, and family members. Diabetes doesn’t take a sick day. Neither should you.