For Canadians living with diabetes, even a common cold or stomach bug can cause serious problems. Managing blood sugar when sick is one of the most important skills a diabetic patient can have. Illness triggers your body to release stress hormones, and those hormones push blood sugar levels higher — sometimes dangerously high. This guide explains what to watch for, what to do, and when to get help.
Why Illness Makes Blood Sugar Harder to Control
When you get sick, your body fights back by releasing hormones like cortisol and adrenaline. These hormones help you recover, but they also raise your blood sugar. For people without diabetes, the body adjusts automatically. For people with diabetes, that adjustment does not happen on its own.
Even a mild infection — like a sinus cold or a urinary tract infection — can cause blood sugar to spike sharply. In some cases, this can lead to two serious complications: diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemic state (HHS). Both are medical emergencies. According to Health Canada, diabetes complications are a leading cause of preventable hospitalisations across the country.
Furthermore, stress from surgery, exams, or emotional difficulties can have the same effect on blood sugar as a physical illness. This means sick-day rules apply to more situations than most people realise.
Managing Blood Sugar When Sick: The Basics
The most important rule is simple: do not stop taking your diabetes medication, even if you feel too unwell to eat. Many people make the mistake of skipping insulin or pills when they cannot keep food down. However, your blood sugar can still rise even without any food intake.
If you take insulin, your dose may need to be adjusted based on your current blood sugar readings and how much you are eating. Your diabetes care team should give you a personalised sick-day plan in advance. If you do not have one, contact your family doctor or a walk-in clinic to get guidance before you get sick.
What to Do If You Cannot Keep Medication Down
Vomiting and diarrhoea make it hard to take oral medications. If you cannot keep your diabetes pills down, call your doctor right away. Do not simply skip your medication and hope for the best. Your doctor may need to temporarily adjust or pause certain medications — especially those in the sulfonylurea class — and provide you with new instructions.
If you are on insulin and cannot keep food down, you still need some form of insulin coverage. Your doctor can guide you on the right dose to use based on your blood sugar levels. Never adjust your insulin dose on your own without professional advice.
Eating and Drinking During Illness
Staying hydrated is critical when you are sick with diabetes. Drink plenty of fluids throughout the day — water and unsweetened herbal tea are the best choices. For children with diabetes, encourage fluids regularly to prevent dehydration, even during the night.
If your blood sugar is above 13.3 mmol/L (240 mg/dL), stick to sugar-free fluids like water or plain tea. Avoid juice, regular pop, or sweetened drinks at this level. If your blood sugar is lower and you cannot eat your normal meals, try easy-to-digest foods like broth-based soup, unsweetened applesauce, or plain crackers.
Carbohydrate Targets During Illness
Try to take in about 50 grams of carbohydrates every three to four hours. This keeps your body fuelled without causing major spikes. If solid food is not possible, sugar-containing liquids like fruit juice or milk can serve as a temporary substitute. However, always balance this with your blood sugar readings and your doctor’s guidance.
In addition, if you are on a carbohydrate-restricted diet normally, sick days may require temporary adjustments. Talk to your diabetes care team ahead of time so you have a clear plan ready to follow.
How to Monitor Blood Sugar and Ketones at Home
During any illness, check your blood sugar every three to four hours. If your readings are high or rising, check through the night as well. Do not assume you are stable just because you checked once in the morning.
If your blood sugar goes above 16.7 mmol/L (300 mg/dL), you also need to check for ketones. Ketones are chemicals that build up when your body burns fat for energy instead of glucose. High ketone levels are a warning sign of DKA. You can test for ketones at home using urine test strips, which are available at most Canadian pharmacies without a prescription.
Special Note for People on SGLT2 Inhibitors
If you take an SGLT2 inhibitor — such as dapagliflozin (Farxiga) or empagliflozin (Jardiance) — you need to be extra careful. These medications work by removing glucose through your urine. As a result, your blood sugar reading may look normal even when ketones are dangerously high. This is called euglycaemic DKA, and it is a serious risk.
Always check both your blood sugar and your urine ketones when you are sick and taking one of these medications. The Mayo Clinic explains the warning signs of diabetic ketoacidosis in detail, and it is worth reviewing them before you need them.
How Often Should You Test for Ketones?
Insulin-dependent diabetics should test for urine ketones every six to twelve hours during illness — especially if blood sugar is above 16.7 mmol/L. Children with diabetes should be tested every six hours, including overnight. If ketone tests come back positive, contact your doctor immediately.
Physical Signs to Watch During Illness
When blood sugar rises above 16.7 mmol/L, monitor your physical symptoms closely. There are several warning signs that indicate your condition is getting worse and that you need medical attention quickly.
Watch for these physical changes:
Weight loss: rapid weight loss can signal serious dehydration
Fast or laboured breathing: breathing faster than normal may indicate DKA
Rapid heart rate: a fast pulse can be a sign your body is under serious stress
Fever: a temperature above 38°C (100.4°F) needs prompt attention
Low-grade fever: even 37.5–38°C warrants careful monitoring
Nausea or vomiting that does not stop: this prevents you from taking medication or staying hydrated
Confusion or drowsiness: these can be signs of a diabetic emergency
According to the World Health Organization’s diabetes fact sheet, early recognition of these warning signs significantly reduces the risk of serious hospitalisation.
When to See a Doctor
If you have diabetes and you get sick, do not wait too long to seek help. Contact your family doctor as soon as possible — most provincial health plans cover these visits at no direct cost to you. If your family doctor is not available, a walk-in clinic can help you manage the immediate situation.
Go to the nearest emergency room or call 911 immediately if you experience any of the following:
Blood sugar above 16.7 mmol/L (300 mg/dL) that does not come down
Positive ketone test results
Vomiting or diarrhoea lasting more than six hours
Signs of dehydration such as dry mouth, dark urine, or dizziness
Confusion, extreme drowsiness, or difficulty staying awake
Rapid or difficult breathing
Chest pain
Children with diabetes should be assessed sooner rather than later. If a child has any of the symptoms above, or if you are unsure, err on the side of caution and go to an emergency department. Always consult your doctor or healthcare provider before making any changes to your diabetes treatment plan.
Frequently Asked Questions
Should I keep taking my diabetes medication when I am sick?
Yes — do not stop your diabetes medication without talking to your doctor first. Managing blood sugar when sick often requires continued medication, and sometimes even higher doses of insulin. Stopping medication during illness can lead to serious complications like diabetic ketoacidosis.
How often should I check my blood sugar when I am sick?
Check your blood sugar every three to four hours during illness. If your levels are high or rising, check throughout the night as well. Frequent monitoring is the key to managing blood sugar when sick and catching problems early.
What are ketones and why do they matter when I am sick?
Ketones are chemicals your body produces when it burns fat for energy instead of glucose. High ketone levels are a warning sign of diabetic ketoacidosis (DKA), which is a medical emergency. You can test for ketones using urine strips available at your local Canadian pharmacy.
What should I eat and drink when I am sick and have diabetes?
Stay well hydrated with water and unsweetened tea. Aim for about 50 grams of carbohydrates every three to four hours from easy-to-digest foods like broth, plain crackers, or applesauce. If your blood sugar is above 13.3 mmol/L, avoid sugary drinks and stick to sugar-free fluids.
Can emotional stress raise blood sugar in diabetics?
Yes, emotional stress — such as major life events, exams, or anxiety — can trigger the same stress hormones as a physical illness and raise blood sugar significantly. Managing blood sugar when sick applies to emotional stress situations as well. Speak to your family doctor if stress is making your diabetes harder to control.
When should I go to the emergency room for high blood sugar?
Go to the emergency room if your blood sugar stays above 16.7 mmol/L and will not come down, if your ketone test is positive, or if you are vomiting and cannot keep fluids down for more than six hours. Confusion, rapid breathing, or chest pain are also signs to call 911 immediately.
Key Takeaways
Never stop your diabetes medication when you get sick — even if you cannot eat, blood sugar can still rise.
Check your blood sugar every three to four hours during any illness, and overnight if levels are high.
Test for ketones if your blood sugar goes above 16.7 mmol/L (300 mg/dL), especially if you use insulin.
Stay hydrated with water and unsweetened fluids. Children need encouragement to drink regularly.
SGLT2 inhibitor users must check ketones even when blood sugar looks normal during illness.
Contact your family doctor or a walk-in clinic early — do not wait until symptoms become severe.
Go to the emergency room immediately if you experience confusion, rapid breathing, persistent vomiting, or positive ketone results.
Always speak with your doctor or diabetes care team before changing your treatment plan. This article is for general information only and does not replace personalised medical advice.
