Sick Day Rules: Managing Diabetes Through Fever, Flu, Dengue and Stomach Bugs

You wake up with a fever. Your throat hurts, you have not eaten since last night, and you feel too tired to think about anything else. Then you check your sugar out of habit and the number is far higher than usual—even though you have barely eaten a thing.

This surprises a lot of people, and it can be frightening if nobody has explained it. It is not a sign that you have done something wrong. It is simply what illness does to a body that is managing diabetes, and it is predictable enough that doctors have a name for the plan you follow through it: sick day rules.

Why Illness Raises Blood Sugar—Even When You Are Not Eating

When your body fights an infection, it releases stress hormones such as cortisol and adrenaline. These hormones tell your liver to push stored glucose into the bloodstream to fuel the immune response, and at the same time they make your cells more resistant to insulin. The result is a blood sugar that climbs on its own, without a single bite of rice or roti.

So a fever, a chest infection, a urinary tract infection, dengue, typhoid or a bad stomach bug can all raise your readings. And if you happen to be vomiting or have diarrhoea at the same time, you are also losing fluid quickly—which concentrates the blood and can push readings higher still while draining your energy.

The Core Sick Day Rules

These are the principles that show up consistently in guidance from the American Diabetes Association, Diabetes UK and NHS diabetes services. Think of them as the shape of the plan—your own doctor fills in the specific numbers for you.

1. 1Check your blood sugar more often. Diabetes UK advises checking at least every four hours during illness, including overnight. Some NHS sick day protocols for people on insulin ask for checks every two hours.
2. 2Do not stop your insulin. Your body needs insulin during illness even if you are not eating. NHS sick day guidance is explicit about this—stopping insulin during illness risks diabetic ketoacidosis (DKA). Doses may need adjusting, but that is a conversation with your doctor, not a decision to make alone.
3. 3Keep drinking. South Tees NHS guidance suggests at least 100 ml of water or sugar-free fluid every hour. The ADA suggests alternating water and electrolyte drinks, and taking small sips roughly every 15 minutes if fluids are hard to keep down.
4. 4Eat little and often if you can. Diabetes UK advises small, frequent intake rather than full meals. If you genuinely cannot eat solid food, fluids that contain some carbohydrate become important—especially if your readings are running low.
5. 5Check ketones if your sugar is high. The ADA advises testing ketones every four to six hours during illness when blood glucose is above 200 mg/dL.
6. 6Rest, and tell someone. Do not manage a significant illness silently. A family member who knows your readings and your plan is a genuine safety measure.

Understanding Ketones

When cells cannot get enough glucose because insulin is not working well enough, the body starts breaking down fat for fuel instead. Ketones are the by-product of that process. In small amounts they are harmless; in large amounts they turn the blood acidic, which is the medical emergency called diabetic ketoacidosis.

Blood ketone meters and urine ketone strips are both available in Pakistani pharmacies, and they are worth having at home before you need them. South Tees NHS guidance interprets blood ketone readings roughly as follows:

Dengue, Typhoid and Diabetes: Why Extra Care Matters Here

Dengue is a seasonal reality in much of Pakistan, and it deserves its own mention. A 2024 meta-analysis published in PLOS Neglected Tropical Diseases, pooling 342,873 laboratory-confirmed patients across 27 studies, found that a diagnosis of diabetes was associated with roughly a three-fold increase in the odds of severe dengue (odds ratio 3.39; 95% CI 2.46–4.68).

That number is not a reason to panic, and it is not a prediction about you. Most people with diabetes who get dengue recover. What it does mean is that the usual advice to "wait and see how you feel in a few days" fits you less well than it fits someone without diabetes. Get tested early, tell whoever treats you that you have diabetes, monitor more closely than you otherwise would, and take fluid intake seriously—dengue and dehydration are a difficult combination on their own, before blood sugar is even involved.

The same early-contact principle applies to typhoid, gastroenteritis and any infection that comes with sustained vomiting or diarrhoea. Illnesses that empty you of fluid are the ones most likely to turn a manageable few days into a hospital admission.

The Medication Question: Which Tablets Pause, Which Continue

This is the part people most often get wrong, in both directions—some stop everything, some continue everything. Neither is right, and the correct answer depends on which medicines you take.

NHS sick day guidance for Type 2 diabetes describes a specific set of medicines that are commonly paused during a dehydrating illness—when you are vomiting, having diarrhoea, or simply not eating and drinking normally. Metformin, SGLT2 inhibitors (the '-gliflozin' medicines) and sulfonylureas fall into that group, because dehydration changes how the kidneys handle them. Insulin is continued, with dose adjustment. GLP-1 medicines are generally continued. Paused medicines are restarted once you are eating and drinking normally again.

When To Stop Waiting and Get Help

The ADA's sick day guide lists clear triggers for calling your doctor or going to the emergency room. If any of these apply, the answer is medical care now—not another few hours of watching.

• Vomiting or diarrhoea continuing for more than four hours
• Moderate to large ketones, or breath that smells sweet or fruity
• Fever above 101°F (38.3°C) lasting more than 24 hours
• Blood glucose above 300 mg/dL on two readings despite taking corrections
• Signs of dehydration such as dizziness or dark urine
• Any uncertainty about what dose of medication to take while sick

South Tees NHS guidance adds breathing faster than normal, persistent stomach pain and simply not improving after six hours to that list. Confusion or drowsiness in someone who is unwell with diabetes always warrants immediate care.

“Going to the hospital and being told you were fine is a good outcome. Waiting at home because you did not want to make a fuss is how a manageable illness becomes a serious one.”

Build the Kit Before You Need It

The ADA recommends keeping a sick day kit assembled in advance. Adapted for a Pakistani household, that looks like:

• Your glucometer, spare batteries, and enough test strips for frequent checking
• Ketone test strips (blood or urine) that are within their expiry date
• At least a week's supply of your diabetes medicines, rotated so nothing expires
• Insulin and pen needles if prescribed, stored correctly
• Glucose tablets or gel, and glucagon if your doctor has prescribed it
• A working thermometer
• Oral rehydration salts (ORS) and bottled water
• Over-the-counter medicines your doctor has already approved for you
• A written card with your doctor's number, your medicine list, and your agreed sick day plan

After You Recover

Blood sugar does not always snap back the moment the fever breaks. It is common for readings to stay somewhat elevated for a few days as your body finishes clearing the infection and your appetite returns. Keep checking a little more often than usual until your numbers settle into their familiar pattern, and restart any paused medicines only once you are eating and drinking normally again.

And if the illness was significant, mention it at your next appointment. A cluster of high readings across one week of dengue is a very different story from a gradual upward drift over three months—but only if your doctor can see which one it was.

Keep a record of your sick days

Logging readings, temperature and what you managed to eat during an illness gives your doctor a clear picture of what actually happened—and helps you recognise your own patterns next time.

Log a reading (opens Diatic on Google Play in a new tab)