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

When You’re Sick and Have Diabetes, Your Body Isn’t Playing Fair

Feeling under the weather is bad enough. But if you have diabetes, a cold, flu, or stomach bug can turn into a medical emergency fast. Your body releases stress hormones when you’re sick - cortisol, adrenaline - and they make your liver dump extra glucose into your blood. Even if you’re not eating, your blood sugar can spike. And if you skip insulin because you feel too nauseous to eat? That’s when ketones start building up. And that’s when diabetic ketoacidosis - DKA - becomes a real threat.

DKA isn’t rare. In 2022, the CDC found it caused nearly 1 in 4 diabetes-related hospital stays. And for Type 1 diabetes, it’s the leading cause of death in people under 24. The good news? Almost all DKA cases during illness are preventable. You just need to know the rules - and follow them, even when you feel awful.

Never Skip Your Basal Insulin - Not Even for a Day

Your long-acting insulin - whether it’s Lantus, Levemir, Basaglar, or another - isn’t just for meals. It’s your body’s baseline safety net. When you’re sick, your insulin needs don’t disappear. They often go up.

People think: "I didn’t eat breakfast. I won’t eat lunch. So I don’t need insulin." That’s the biggest mistake. Skipping basal insulin during illness is the top reason people end up in the ER with DKA. Even if you’re vomiting, even if you’re sleeping all day, even if your blood sugar is 150 mg/dL - keep giving your basal dose. The American Diabetes Association and the International Diabetes Federation both say: never reduce basal insulin below 80% of your normal dose during illness.

If you’re on an insulin pump, you might need to increase your basal rate. Most experts recommend a +20% boost for 12 hours if your blood ketones hit 1.0 mmol/L or higher. If you’re on injections, you may need to add a correction dose every 3-4 hours, even if you’re not eating. Your body still needs insulin to stop fat breakdown and prevent ketone buildup.

One patient on Reddit, u/Type1Techie, said: "I followed the +20% basal rule during my flu. My blood sugar stayed between 150-200 mg/dL. No ketones. No ER trip." That’s the goal.

Hydration Isn’t Optional - It’s Your Lifeline

When your blood sugar is high, your kidneys work overtime to flush out the extra glucose. That means you’re peeing a lot - and losing water, electrolytes, and sodium. Dehydration makes everything worse. It makes your blood sugar climb higher. It makes ketones concentrate in your blood. And it can lead to shock.

So drink. Constantly. Not "when you’re thirsty." Not "if you can keep it down." Every hour, even if you’re just sipping.

For adults: Aim for 6-8 ounces of fluid every hour. That’s about a cup. For kids: Use the "age in ounces" rule - a 10-year-old needs 10 ounces per hour. But here’s the catch: not all fluids are created equal.

• If your blood sugar is above 180 mg/dL: Stick to sugar-free fluids - water, unsweetened tea, broth, sugar-free electrolyte drinks.
• If your blood sugar is between 100-180 mg/dL: Alternate between water and fluids with 15 grams of carbs - like half a cup of regular Gatorade or 4 oz of apple juice.
• If your blood sugar is below 100 mg/dL: Use sugary fluids to prevent lows - regular soda, juice, or oral rehydration solutions.

Don’t rely on feeling thirsty. By the time you’re thirsty, you’re already dehydrated. Set a timer. Every hour, drink. Even if you’re vomiting, try to sip slowly. If you can’t keep anything down for more than 4 hours, call your doctor or go to urgent care. IV fluids can save your life.

Ketone Checks: When to Test, What the Numbers Mean

Ketones are your body’s emergency fuel - fat burned for energy because it doesn’t have enough insulin to use glucose. Small amounts are normal. High amounts? That’s DKA waiting to happen.

Test for ketones when your blood sugar is above 240 mg/dL - or if you’re feeling nauseous, vomiting, or have stomach pain. Don’t wait. Test every 2-3 hours during illness.

There are two kinds of ketone tests: urine strips and blood meters. Blood ketone meters are more accurate and faster. Urine strips can be misleading - they show ketones that were made hours ago, not what’s happening now. If you have a blood ketone meter, use it.

Here’s what the numbers mean:

• Below 0.6 mmol/L: Normal. Keep monitoring.
• 0.6-1.5 mmol/L: Moderate ketones. Increase insulin (basal + correction), drink more fluids, retest in 2 hours.
• 1.5 mmol/L or higher: High ketones. This is dangerous. Call your doctor immediately. If you’re on a pump, change your infusion site. If you’re vomiting, can’t drink, or feel confused - go to the ER. Don’t wait.

One patient, u/SickDayStruggles, said: "I ignored ketones because my urine strip said ‘small.’ I thought it was fine. By morning, my blood sugar was 420 mg/dL and ketones were 22 mmol/L. I was in DKA for 18 hours before someone told me to test blood, not urine." Don’t be that person. Blood ketones are your real-time alarm.

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

Not all diabetes is the same - and your sick day plan should reflect that.

If you have Type 1 diabetes: You are at high risk for DKA. You must test ketones every time your blood sugar is over 240 mg/dL. You must never skip insulin. You may need to increase your dose even if you’re not eating.

If you have Type 2 diabetes and take insulin: Same rules apply. Ketones can still build up. Test them. Don’t skip insulin.

If you have Type 2 and only take pills (like metformin or GLP-1s): You’re at lower risk for DKA - but not zero risk. If your blood sugar stays above 240 mg/dL for more than 24 hours, or if you’re vomiting and can’t keep food down, check ketones. And call your doctor. Some Type 2 patients need temporary insulin during serious illness - even if they’ve never taken it before.

The CDC recommends Type 2 patients aim for blood sugar between 110-180 mg/dL during illness. Tighter than normal, but looser than Type 1 targets. Why? Because you’re more likely to crash from low blood sugar if you’re not eating. Balance is key.

Your Sick Day Kit: What to Have Ready

Don’t wait until you’re sick to figure this out. Build a kit now - and keep it stocked.

• Unexpired blood ketone test strips (check expiration - expired strips give false negatives)
• Glucose meter and extra batteries
• Insulin (at least 7 days’ worth, stored properly)
• Fast-acting carbs for lows: glucose tabs, juice boxes, honey packets
• Sugar-free fluids: water, sugar-free electrolyte drinks
• Sugary fluids: regular soda, juice, Gatorade
• Thermometer, measuring cup (8 oz), and a notebook to log blood sugar, ketones, fluids, and symptoms
• Emergency contact list: your endocrinologist, pharmacy, and a trusted friend or family member

Also, know your insulin’s shelf life. Once opened, most pens last 28 days. Don’t use old insulin - it loses potency. If your blood sugar won’t come down, and you’ve taken enough insulin, suspect bad insulin. Swap it out.

What Not to Do - Common Mistakes That Put You at Risk

• Skipping insulin because you’re not eating - this is the #1 cause of DKA during illness.
• Using urine strips only - they’re outdated. Blood ketone meters are more accurate and faster.
• Drinking sugary drinks when blood sugar is high - that just makes it worse.
• Ignoring vomiting - if you can’t keep fluids down for more than 4 hours, get help.
• Taking OTC meds without checking - many cold and flu medicines contain sugar or alcohol. Read labels. Look for "sugar-free" or "diabetic-friendly."
• Waiting to call your doctor - if ketones are high, you’re confused, breathing fast, or smell fruity, don’t wait for office hours. Go to urgent care or the ER.

When to Call for Help - The Red Flags

You don’t need to guess when it’s time to get help. Here’s the clear list:

• Blood ketones above 1.5 mmol/L
• Blood sugar over 300 mg/dL for two checks in a row, and not coming down with insulin
• Vomiting for more than 4 hours - even if you’re drinking
• Difficulty breathing, rapid breathing, or fruity-smelling breath
• Confusion, drowsiness, or inability to stay awake
• Weight loss of 5 pounds or more in 24-48 hours

If any of these happen - go to the emergency room. Don’t wait. Don’t text your doctor. Don’t hope it gets better. DKA is treatable - but only if caught early.

What’s New in 2026 - And What’s Still Missing

Guidelines keep improving. In 2023, the ADA added new advice for people using continuous glucose monitors (CGMs). If more than half your readings are over 250 mg/dL for 12 hours straight - treat it like a high blood sugar event. Check ketones. Adjust insulin.

Also, viral illnesses like flu and RSV cause 37% more insulin resistance than bacterial infections. So if you’re sick with the flu, expect to need more insulin than you would with a cold.

But here’s the gap: most guidelines still don’t fully address how to manage sick days with closed-loop insulin systems (like the Omnipod 5 or MiniMed 780G). These systems pause insulin automatically when glucose drops - but during illness, you need more insulin, not less. Many users report their pumps don’t respond correctly to sick-day highs. That’s a dangerous blind spot.

And there’s still confusion. A 2022 survey found 74% of people with diabetes found ketone testing confusing. Half didn’t know whether to use urine or blood tests. That’s why clear, simple, consistent advice matters.

Final Thought: Preparation Saves Lives

There’s no magic pill for sick days with diabetes. But there is a simple, proven plan: keep insulin going, drink constantly, test ketones early, and know when to call for help. Build your kit now. Write down your plan. Practice the steps before you’re sick. When the flu hits, you won’t have time to think - you’ll have to act. And if you’ve prepared, you’ll act right.