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

When you're sick, your body fights infection by releasing stress hormones like cortisol and adrenaline. For someone with diabetes, this isn't just a cold or flu-it's a metabolic emergency. Blood sugar can spike even if you're not eating. Ketones can build up. Dehydration sets in fast. And skipping insulin? That’s how diabetic ketoacidosis (DKA) starts. DKA sent nearly 1 in 4 people with diabetes to the hospital in 2022, and it can be deadly. But it doesn’t have to be. Knowing the right sick day rules can keep you out of the ER.

Never Skip Your Long-Acting Insulin

Even if you can’t eat, even if you’re vomiting, even if your blood sugar feels normal-you still need your long-acting insulin. This isn’t optional. It’s biology. Your liver keeps making glucose while you’re sick, and your body becomes resistant to insulin. If you stop your basal insulin-whether it’s Lantus, Levemir, or Basaglar-you’re cutting off the one thing holding back ketone production.

Studies show that up to 30% of DKA cases happen because people reduce or skip insulin when they’re ill. That’s not a myth. It’s data from the International Diabetes Federation. If you use an insulin pump, your basal rate might need a +20% boost for 12 hours if ketones are moderate or large. If you use injections, you still need your usual daily dose. Don’t guess. Don’t wait. Keep it going.

Check Blood Sugar Every 2-4 Hours

When you’re healthy, checking your blood sugar twice a day might feel enough. When you’re sick, that’s not enough. You need to check every 2 to 3 hours if you’re a child, and every 3 to 4 hours if you’re an adult. Set alarms. Write it down. Use your CGM alerts if you have one.

Here’s what the numbers mean:

• Below 100 mg/dL: You’re at risk for low blood sugar. Time to take in carbs.
• 100-180 mg/dL: This is your target zone. Keep hydrating and monitor ketones.
• Above 180 mg/dL: Start checking for ketones. You’re in danger zone.
• Above 240 mg/dL: Test for ketones immediately. If they’re present, call your doctor.

Don’t wait until you feel terrible. High blood sugar doesn’t always come with symptoms. That’s why checking regularly saves lives.

Hydration Isn’t Just About Drinking Water

When your blood sugar is high, your body pulls fluid from your cells to flush out sugar through urine. You’re losing water fast. Dehydration makes everything worse-higher blood sugar, higher ketones, more nausea.

The rule isn’t just “drink more.” It’s “drink the right thing at the right time.”

• If your blood sugar is above 180 mg/dL: Stick to sugar-free fluids-water, unsweetened tea, broth, or sugar-free electrolyte drinks.
• If your blood sugar is between 100 and 180 mg/dL: Alternate between water and fluids with 15 grams of carbs. That’s half a cup of regular soda, 4 oz of Gatorade, or 1 small juice box.
• If your blood sugar drops below 100 mg/dL: Take in 15 grams of fast-acting carbs-glucose tabs, juice, or regular soda-to prevent lows.

For adults, aim for 6-8 ounces of fluid every hour. For kids, use the “age in ounces” rule: a 10-year-old needs about 10 ounces per hour. 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 urgent care. IV fluids are better than waiting for DKA to set in.

Test for Ketones-But Do It Right

Ketones are your body burning fat for fuel because it can’t use glucose. That sounds harmless. But when ketones pile up in your blood, they turn your blood acidic. That’s DKA. And it kills.

You test for ketones when your blood sugar is above 240 mg/dL-or if you feel nauseous, have stomach pain, or your breath smells fruity. But here’s the mistake most people make: they use urine strips.

Urine ketone strips are outdated. They show ketones from hours ago. Blood ketone meters give you real-time numbers. If you have a meter that tests blood ketones, use it. If you only have urine strips, know this:

• Trace or small: Monitor closely. Recheck in 2 hours.
• Moderate or large: Call your doctor. You need help now.

Blood ketone levels are clearer:

• 0.6-1.5 mmol/L: Moderate ketones. Increase insulin, hydrate, recheck in 2 hours.
• Above 1.5 mmol/L: High ketones. Take a correction dose of insulin. Change your pump site if you use one. Call your doctor or go to the ER.

A 2022 survey found 42% of people with diabetes didn’t know blood ketone meters were more accurate than urine strips. Don’t be one of them.

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

People with Type 1 diabetes are at higher risk for DKA because they make no insulin. That’s why ketone checks are mandatory when sick.

People with Type 2 diabetes usually don’t get DKA-but they can. Especially if they’re on insulin. If you take insulin, treat yourself like a Type 1 during illness. Check ketones. Don’t skip insulin.

If you’re on pills only-like metformin or GLP-1s-you don’t need ketone checks unless your blood sugar stays above 240 mg/dL for more than a day. But you still need to monitor sugar and fluids. Some pills, like SGLT2 inhibitors, can increase DKA risk even without high blood sugar. Talk to your doctor about your specific meds.

What’s in Your Sick Day Kit?

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

• Unexpired blood ketone test strips (they last 6 months after opening)
• Glucose tabs or juice boxes for lows
• Sugar-free electrolyte drinks
• Regular soda or juice for highs
• Thermometer
• Measuring cup (to track fluid intake)
• Written plan from your doctor with insulin adjustment rules
• 7-day supply of all medications

Many people forget the measuring cup. Guessing “a few sips” won’t cut it. You need to know if you’re drinking 6 ounces or 12.

When to Call for Help

You don’t have to figure this out alone. But you need to know when to call.

Call your doctor or go to the ER if:

• Your blood sugar stays above 240 mg/dL for more than 6 hours despite insulin and fluids
• You have moderate or large ketones on blood or urine test
• You’re vomiting and can’t keep fluids down for 4+ hours
• You’re confused, breathing fast, or have abdominal pain
• You’ve lost 5 pounds or more in a few days

One Reddit user wrote: “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 kind of confusion that kills. Don’t rely on random advice. Have your plan written down. Stick to it.

Watch Out for Hidden Sugars and Alcohol

Over-the-counter cold medicines? Many contain sugar or alcohol. That’s a double trap. Sugar spikes your blood sugar. Alcohol can mask low blood sugar symptoms and make dehydration worse.

Always check labels. Look for “sugar-free” versions. Avoid syrups. Choose pills over liquids. If you must use a liquid, pick one with no sugar or alcohol. And if you’re unsure, call your pharmacist. They’ve seen this before.

What About New Tech? CGMs and Closed-Loop Systems

If you use a CGM or closed-loop system (like a MiniMed or Omnipod), your alarms might go off nonstop when you’re sick. That’s normal. But don’t turn them off.

Your device doesn’t know you’re sick. It still thinks you’re in control. If your glucose is above 250 mg/dL for more than half the readings over 12 hours, treat it like a high. Give insulin. Hydrate. Check ketones.

Right now, most automated systems don’t adjust for illness. They don’t know you have the flu. So you have to be the one stepping in. Experts warn this is a dangerous gap in technology. Don’t assume your pump will save you. You’re still the boss.

Final Thought: This Is About Survival, Not Perfection

You don’t need perfect blood sugar numbers when you’re sick. You need to stay alive. Keep insulin flowing. Keep fluids coming. Keep checking ketones. If you do those three things, you’re doing better than most.

Diabetes doesn’t take a sick day. Neither should you. The rules are simple. The stakes are high. Know them. Practice them. Keep your kit ready. And if you’re ever unsure-call your diabetes team. The ADA’s helpline answers 12,000 sick-day calls every month for a reason. You’re not alone.