Why being sick is a big deal for diabetes
A common cold or stomach bug is an annoyance for most people, but when you have diabetes, illness deserves a real plan. The reason comes down to hormones. When your body fights an infection, it releases stress hormones like cortisol, adrenaline, and glucagon that raise blood sugar and make your insulin work less effectively. So even though you may be eating less than usual, your glucose can climb, sometimes dramatically, into the 300s or higher.
This is why illness is one of the leading triggers for diabetes emergencies. In type 1 diabetes, and sometimes type 2, uncontrolled highs during sickness can tip into diabetic ketoacidosis, a dangerous buildup of acid in the blood that can develop within hours once insulin falls short. On the other side, if a stomach bug stops you from eating while you keep taking glucose-lowering medication, you can swing low instead. Having clear sick day rules ready before you get sick means you are not trying to make tricky decisions while feverish, nauseated, and foggy.
Every person with diabetes should have a personal sick day plan worked out with their care team in advance. The general principles below apply broadly, but the specific numbers, like how much extra insulin to give, depend on your own treatment, your usual doses, and your type of diabetes. Think of this as the framework to discuss with your doctor or diabetes educator, then write down, save in your phone, and stick on the fridge where a family member can find it.
Never stop your insulin or diabetes medication
The single most important sick day rule for anyone on insulin is this: do not stop your insulin, even if you are not eating. This is the most dangerous and most common mistake. It seems logical to skip your dose when no food is going in, but during illness your body still needs background insulin, and often more of it, to handle the sugar your liver keeps releasing under stress. Stopping insulin during illness is a fast route to ketoacidosis, sometimes within half a day.
Your basal, or long-acting, insulin should generally continue at its usual dose, and you may need extra rapid-acting insulin to correct the highs that illness causes. Many people need 10 to 20 percent more insulin than usual while sick, and some need more during a serious infection, though this varies and your plan should spell out the numbers. Some oral medications need a different approach. Metformin and SGLT2 inhibitors (drugs ending in -gliflozin, like empagliflozin and dapagliflozin) are often paused during significant illness, especially if you are dehydrated or vomiting, because they can raise the risk of complications. Metformin can build up if the kidneys are stressed, and SGLT2 inhibitors raise the risk of euglycemic ketoacidosis when you are not eating. Your doctor can tell you which of your medications to hold and which to continue.
- Keep taking your basal (long-acting) insulin, usually at the normal dose
- Be ready to add correction doses of rapid-acting insulin for highs
- Ask your team in advance which oral drugs to pause when sick
- Never skip insulin just because you are eating less
Check blood sugar and ketones more often
When you are well, you might test your blood sugar a few times a day. When you are sick, ramp that up. Check your glucose every two to four hours, around the clock if needed, including overnight if your numbers are running high. Illness makes blood sugar unpredictable, and frequent checks let you catch a dangerous trend early rather than discovering it too late. If you use a continuous glucose monitor, keep an eye on the trend arrows, but confirm with a fingerstick if a reading does not match how you feel, since dehydration can affect sensor accuracy.
Just as important is checking for ketones, the acidic byproducts that signal your body is burning fat for fuel because it lacks insulin. Test ketones whenever your blood sugar is above 240 mg/dL (13.3 mmol/L), and any time you feel nauseated or are vomiting, regardless of your glucose number, since euglycemic ketoacidosis can happen with normal sugars. A blood ketone meter that measures beta-hydroxybutyrate is more accurate and timely than urine strips. A blood ketone reading under 0.6 mmol/L is fine, 0.6 to 1.5 mmol/L means take extra fluids and insulin and recheck in one to two hours, and anything above 1.5 mmol/L, especially climbing, means you should contact your care team. Rising ketones with vomiting is a reason to seek urgent help rather than wait.
Stay hydrated and keep some carbs going in
Dehydration makes everything worse during a diabetic sick day. High blood sugar pulls fluid out of your body through frequent urination, and fever, vomiting, or diarrhea drain it faster. The goal is to drink plenty, aiming for roughly a cup (about 240 mL) of fluid every hour while you are awake, sipped slowly rather than gulped. If your blood sugar is high, choose sugar-free fluids like water, broth, herbal tea, or diet drinks. If it is low or normal and you cannot eat, switch to fluids that contain sugar to keep your glucose up and let you keep taking insulin.
Food can be tricky when you feel nauseous, but your body still needs some carbohydrate, especially if you take insulin. If you cannot manage normal meals, aim for small amounts of easy carbs every hour or two, roughly 15 grams at a time. Good options include half a cup of regular soda, fruit juice, ice pops, gelatin, crackers, dry toast, plain rice, or sports drinks. Sipping or nibbling slowly often stays down better than eating a full plate. Replacing lost salts with broth or an oral rehydration solution helps too, particularly if you have been vomiting or have diarrhea, since plain water alone does not restore the sodium and potassium you lose. If you cannot keep even sips of fluid down for several hours, that is a warning sign in itself.
A simple sick day kit to prepare in advance
The time to assemble your supplies is before you get sick, not at 2 a.m. when you feel awful. Keep a small kit stocked in one labeled box and let a family member know where it is and how the basics work. Having everything in one place removes a layer of stress and helps you stick to your plan when your brain is foggy with fever and you are too unwell to run to the pharmacy.
A good sick day kit covers testing, treatment, and information. Check it every few months and replace anything expired, especially ketone strips and glucagon, which have limited shelf lives and degrade once opened or exposed to heat. It is also worth keeping a written list of your current medications and doses inside the kit, so that if you do end up calling for help or going to hospital, you or a relative can hand over accurate information quickly.
- A working glucose meter with plenty of test strips, or a CGM with spare sensors
- In-date blood or urine ketone testing strips
- Extra insulin and a glucagon kit if you use insulin
- Sugar-free and sugar-containing fluids, plus easy carbs like crackers and juice
- A thermometer and basic over-the-counter remedies your doctor approves
- Your written sick day plan, medication list, and your care team's phone numbers
How to adjust insulin doses when you are sick
Illness usually raises blood sugar, so many people on insulin actually need more, not less, even when eating little. A common approach for people on rapid-acting insulin is to add a correction dose every three to four hours when readings stay high, often an extra 10 to 20 percent of your usual total daily insulin spread through the day. For example, someone who normally takes 40 units a day might add 1 to 2 extra correction units of lispro or aspart each time a reading sits above 250 mg/dL (13.9 mmol/L) with ketones present. Never change your long-acting basal insulin, such as glargine or degludec, without guidance, but do keep taking it even if you are not eating.
The numbers that should prompt action are worth memorizing. Check your sugar every two to four hours around the clock while sick, and test for ketones any time you are above 240 mg/dL (13.3 mmol/L), vomiting, or feeling foggy. Moderate or large urine ketones, or a blood ketone meter reading above 1.5 mmol/L, means you need extra insulin and fluids right away and a call to your care team. Sip 4 to 8 ounces of fluid every 30 to 60 minutes, alternating between sugar-free drinks when your sugar is high and carb-containing ones like regular ginger ale or juice when it drops below 100 mg/dL (5.6 mmol/L). Writing these thresholds on a card and taping it inside a cabinet means you are not trying to recall them while feverish and exhausted.
When to call your doctor or go to the hospital
Most mild illnesses can be ridden out at home with frequent monitoring, fluids, and dose adjustments. But some signs mean you have crossed from self-care into needing professional help, and knowing them in advance can be lifesaving. Do not try to tough out the warning signs of ketoacidosis or severe dehydration. When in doubt, make the call. Diabetes teams would far rather hear from you early, when a phone adjustment might fix things, than treat a full emergency later.
Seek urgent medical help if you are vomiting repeatedly and cannot keep fluids down for more than a few hours, if your blood ketones are above 1.5 mmol/L and rising or above 3.0 mmol/L at all, if your blood sugar stays above 240 mg/dL (13.3 mmol/L) despite correction doses, or if you have signs of DKA such as deep rapid breathing, fruity-smelling breath, severe abdominal pain, or confusion. Severe dehydration with dizziness when you stand, a high fever that will not come down, an illness dragging on with no improvement after a couple of days, or simply feeling that something is seriously wrong are all good reasons to seek care. Vulnerable groups, including young children, older adults, pregnant women, and anyone living alone, should have a lower threshold for calling.
These rules are a general guide, and your own plan, agreed with your doctor or diabetes educator, takes priority. If you have not yet built a personal sick day plan, make it a priority at your next visit, well before you actually need it, and ask specifically about your correction doses, which oral drugs to pause, and the exact ketone numbers that should prompt a call. A little preparation turns a scary situation into a manageable one, and it can keep a routine cold from becoming a hospital trip.