Being sick with diabetes is a double challenge: the illness itself drives blood sugar up, often stubbornly, even if you’re barely eating. Stress hormones released during infection or fever cause your liver to dump extra glucose into your bloodstream while simultaneously making your cells less responsive to insulin. The result is blood sugar readings that can climb well above your normal range, sometimes dangerously so. Managing this requires a combination of more frequent monitoring, staying hydrated, adjusting food intake, and in some cases changing your medication doses.
Why Illness Raises Blood Sugar
When your body fights an infection, a cold, the flu, or even a stomach bug, it triggers a stress response. Cortisol, adrenaline, glucagon, and growth hormone all rise. These hormones tell your liver to release stored glucose so your immune system has fuel to work with. At the same time, insulin levels drop and your cells become more resistant to whatever insulin is available. For someone without diabetes, the body compensates automatically. For someone with diabetes, this cascade can send blood sugar soaring, even if you haven’t eaten anything.
This is why you can wake up with a blood sugar of 300 mg/dL during a bad cold despite skipping dinner the night before. The glucose isn’t coming from food. It’s coming from your liver, and your body’s normal braking system isn’t working well enough to stop it.
Check Blood Sugar Every 4 to 6 Hours
During illness, your usual testing schedule isn’t enough. The CDC recommends checking blood sugar every 4 to 6 hours, especially if readings are at or above 250 mg/dL. At that threshold, you should also begin testing for ketones using urine strips or a blood ketone meter. Ketones are acids that build up when your body starts burning fat instead of glucose for energy, and high levels can lead to a dangerous condition called diabetic ketoacidosis (DKA).
If you use a continuous glucose monitor, keep a closer eye on trends than usual. A steady upward arrow during illness warrants action, not just observation. Write down your readings or keep a log on your phone so you can spot patterns and share them with your care team if needed.
Stay Hydrated Aggressively
Dehydration is one of the biggest risks when you’re sick with diabetes. High blood sugar pulls water out of your cells, fever and vomiting accelerate fluid loss, and dehydration in turn concentrates the glucose in your blood, making readings climb even higher. It becomes a vicious cycle.
Aim for at least 8 ounces of fluid per hour while you’re awake. Water is the best choice when blood sugar is elevated. If your blood sugar is dropping too low (below about 70 mg/dL), switch to fluids that contain some sugar, like diluted juice, broth, or an electrolyte drink. Sipping steadily is more effective than trying to drink a large amount at once, especially if you’re nauseous. Small, frequent sips of clear fluids tend to stay down better.
What to Eat When You Can’t Eat
If you can’t keep solid food down, you still need some carbohydrates to prevent your blood sugar from crashing, particularly if you take insulin or certain oral medications. The CDC recommends consuming about 50 grams of carbohydrates every 4 hours when you can’t eat regular meals. That’s roughly equivalent to one cup of applesauce, a cup of juice, six saltine crackers, or a cup of regular (not diet) ginger ale.
This might feel counterintuitive when your blood sugar is running high. But going without any carbohydrates for extended periods, especially while taking diabetes medication, creates a risk of dangerous lows or pushes your body into burning fat for fuel, which increases ketone production. The goal is a steady, modest intake rather than nothing at all or a large meal your stomach can’t handle.
Insulin Adjustments During Illness
If you take insulin, one of the most important sick day rules is simple: never skip your basal (long-acting) insulin. Even if you’re not eating, your liver is still producing glucose, and your basal insulin is what keeps that background production in check. Skipping it is one of the fastest paths to dangerously high blood sugar and DKA.
When blood sugar stays persistently above 250 mg/dL, you may need extra doses of rapid-acting insulin. A common clinical guideline bases these correction doses on your total daily dose (TDD), which is the sum of all your usual insulin units in a day. The extra dose is typically 10% to 20% of your TDD depending on how high your blood sugar has climbed. Rapid-acting insulin corrections can generally be given every 3 to 4 hours as needed.
These adjustments should ideally be discussed with your diabetes care team before you need them. Many endocrinologists provide a written “sick day plan” that spells out exactly how much extra insulin to take at different blood sugar levels. If you don’t have one, calling your doctor’s office or nurse line while you’re sick is worth the effort. Don’t guess at large dose changes on your own.
Medications to Pause When Sick
Certain diabetes medications should be temporarily stopped during illness, particularly if you’re vomiting, unable to eat, or dehydrated. One important category is SGLT2 inhibitors (medications with names ending in “-flozin,” like empagliflozin or dapagliflozin). These drugs work by causing the kidneys to excrete excess glucose through urine, which increases dehydration risk and, more critically, can trigger DKA even when blood sugar readings appear normal.
This is an unusual and dangerous situation: you can develop ketoacidosis with a blood sugar of 150 or 180 mg/dL, which would normally seem fine. Standard urine ketone strips may also underestimate the problem because SGLT2 inhibitors interfere with how ketones show up in urine. If you take one of these medications, stop it when you become sick enough that you can’t eat or drink normally, and don’t restart until you’ve recovered. A blood ketone test (not urine) is the more reliable option if you’re concerned.
Metformin is another medication commonly paused during illness with significant vomiting or dehydration, as it can contribute to a rare but serious buildup of lactic acid. If you’re unsure which of your medications should be held, your pharmacist can often answer this question quickly by phone.
Warning Signs That Need Emergency Care
Most sick days with diabetes are manageable at home with extra monitoring and fluids. But certain symptoms mean the situation has become dangerous. DKA symptoms include vomiting that won’t stop, stomach pain, a fruity or acetone-like smell on your breath, and labored or unusually deep breathing. This is a medical emergency.
Another serious complication, more common in Type 2 diabetes, is hyperosmolar hyperglycemic state (HHS). This occurs when blood sugar climbs above 600 mg/dL for an extended period, leading to severe dehydration, confusion, and sometimes loss of consciousness. HHS develops more gradually than DKA but is equally life-threatening.
On the other end of the spectrum, watch for severe low blood sugar if illness is causing you to vomit up food while your medication is still active. Signs include blurred or double vision, disorientation, clumsiness, and in extreme cases, seizures. If you can’t keep food down and your blood sugar is dropping below 70 mg/dL repeatedly, that’s also a reason to seek medical help rather than trying to manage it alone.
A Practical Sick Day Checklist
- Test blood sugar every 4 to 6 hours and check ketones any time readings exceed 250 mg/dL.
- Drink at least 8 ounces of fluid per hour, choosing water when blood sugar is high and sugar-containing fluids when it’s low.
- Eat 50 grams of carbohydrates every 4 hours if you can’t manage regular meals.
- Never skip basal insulin, even if you’re not eating.
- Stop SGLT2 inhibitors if you can’t eat or drink normally, and ask about pausing metformin during vomiting or dehydration.
- Keep your sick day plan accessible, including your care team’s phone number, your total daily insulin dose, and correction dose instructions.
The best time to prepare for a sick day is before you’re sick. Talk to your care team about a written plan, stock up on ketone strips, keep easy-to-digest carbohydrate sources in the pantry, and make sure you know which medications to hold. When illness hits, those preparations make the difference between a rough few days at home and an avoidable trip to the emergency room.