Nursing care
Sick Day Rules, explained for the bedside and the exam
Written and reviewed by Dana Whitfield, RN, MSN · 6 min read · Updated September 2026
Short answer
Sick day rules mean a person with diabetes keeps taking insulin during illness even when appetite drops, checks blood glucose and ketones more often, and drinks fluids to prevent dehydration. Stopping insulin because intake is low is the single most common route into diabetic ketoacidosis, since illness raises counter-regulatory hormones and glucose regardless of what is eaten.
The idea in one paragraph
Illness raises cortisol, glucagon and catecholamines. These hormones push the liver to release glucose and push fat cells to release fatty acids, and both processes continue whether or not the person is eating. Insulin need therefore does not fall during a stomach bug or a chest infection; it often rises. Sick day rules exist because the intuitive response — stop the insulin since nothing is going in — is exactly backwards, and exactly what produces diabetic ketoacidosis in a person with type 1 diabetes or severe insulin deficiency.
The rule set is short. Keep taking insulin, adjusting the dose with sick day guidance rather than omitting it. Check blood glucose more frequently, typically every two to four hours. Check urine or blood ketones if glucose is persistently above 240 mg/dL (13.3 mmol/L) or per local protocol. Drink fluids to replace losses from fever, vomiting or diarrhoea, using sugar-containing fluids if intake is poor and sugar-free fluids if glucose is already high. Know when to call for help — persistent vomiting, ketones, or glucose that will not come down are all reasons to escalate.
Why it matters clinically
Diabetic ketoacidosis develops fastest in exactly the scenario sick day rules are written for: an unwell person with type 1 diabetes who reasons that skipping a meal means skipping the insulin that covers it. Without insulin, cells cannot take up the glucose the liver is dumping, so glucose climbs while cells starve. The body then breaks down fat for fuel, producing ketones and metabolic acidosis. This can happen over hours in someone on an insulin pump, since pump users carry no long-acting insulin reservoir and a missed bolus removes coverage almost immediately.
The clinical stakes are why sick day rules are taught as a discrete, memorisable protocol rather than left to judgement in the moment. A person feeling nauseated and febrile is not in a good position to reason through endocrine physiology; they need a rule they can follow on autopilot. Nursing teaching that frames insulin omission as dangerous, specifically because illness increases rather than decreases insulin need, closes the gap between what feels intuitive and what is physiologically correct.
How to apply it at the bedside
When a patient with diabetes presents unwell, ask directly whether they have taken their usual insulin doses since the illness began. A history of reduced or omitted insulin during illness is a red flag for evolving ketoacidosis and should prompt an immediate glucose and ketone check, not just a note in the chart. Reinforce, in plain language, that insulin is not optional during illness and that the dose may need adjusting with guidance rather than stopping.
Set an explicit monitoring schedule: blood glucose every two to four hours, ketones checked whenever glucose exceeds the locally defined threshold. Document trends, not single values, since a rising glucose with rising ketones on an unchanged insulin regimen is the pattern that precedes decompensation. Encourage fluid intake matched to glucose level, and confirm the patient or family knows the specific triggers for contacting the diabetes team or presenting to the emergency department: ketones present, vomiting that prevents fluid or insulin intake, or glucose that will not respond to correction doses.
Where students get it wrong
The most common error is assuming that reduced oral intake justifies reduced or withheld insulin. Students reach for the logic that governs many other medications — hold it if the patient is not eating — and apply it to insulin, where it is dangerous. The correct default is the opposite: illness increases insulin resistance and hepatic glucose output, so insulin is continued and often supplemented, guided by glucose and ketone results rather than by appetite.
A second error is treating sick day rules as identical for type 1 and type 2 diabetes. The risk of rapid ketoacidosis is highest in type 1 diabetes and in anyone using an insulin pump, because there is no background insulin reserve once the pump stops delivering. In type 2 diabetes the priority shifts more toward hydration and glucose monitoring, and some oral agents, notably metformin and SGLT2 inhibitors, are typically held during acute illness for reasons unrelated to insulin dosing. Do not extend the metformin-hold logic to insulin.
Worked examples
A 19-year-old with type 1 diabetes has gastroenteritis, is vomiting, and has not eaten since the previous evening. He tells the nurse he skipped his morning insulin because he had nothing to cover. The correct response is to check glucose and ketones immediately, contact the diabetes team for a sick day dosing adjustment, and clarify that basal insulin especially should not be omitted; his risk of ketoacidosis is now elevated and rising.
A 68-year-old with type 2 diabetes on metformin and a basal insulin injection has influenza with a fever of 38.9°C and poor appetite. Appropriate sick day management includes continuing the basal insulin, holding the metformin per usual sick day guidance, checking glucose every four hours, and encouraging small frequent fluids. Ketone testing is less urgent here than for the type 1 patient but should still occur if glucose rises above the threshold.
How the exam tests it
NCLEX items on this topic typically present a patient with diabetes who is unwell and either asks what the nurse should teach about insulin during illness, or asks the nurse to prioritise an action when a patient reports having stopped insulin because they were not eating. The correct answer nearly always affirms that insulin continues during illness, with dose guided by monitoring, and flags the omission itself as the priority finding requiring follow-up.
Distractor answers commonly offer to hold the next insulin dose until the patient can eat, or to wait and recheck glucose later without acting on a reported omission. Both are wrong for the same reason: they treat insulin as intake-dependent rather than illness-dependent. Questions may also test the ketone threshold and the fluid-choice logic — sugar-containing fluids when intake is poor and glucose is not elevated, sugar-free fluids when glucose is already high — so know both numbers, not just the headline rule.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our endocrine practice questions are the closest set to what this page covers.
Common questions
Should a patient with type 1 diabetes ever stop insulin when they are sick?
No. Insulin is continued through illness because counter-regulatory hormones raise glucose and ketone production regardless of oral intake. Doses may be adjusted with clinical guidance, but omission is what precipitates diabetic ketoacidosis.
How often should glucose be checked during sick days?
Every two to four hours is standard advice, more often if glucose is unstable or trending upward. This frequency allows early detection of the rising glucose and ketone pattern that precedes decompensation.
At what glucose level should ketones be checked?
A common threshold is above 240 mg/dL (13.3 mmol/L), though local protocols vary. Ketones should also be checked whenever the patient feels unwell out of proportion to the glucose reading, or is vomiting.
Do sick day rules apply the same way in type 2 diabetes?
The principle of continuing insulin still applies, but the urgency around ketosis is lower than in type 1 diabetes. Oral agents such as metformin and SGLT2 inhibitors are often held during acute illness, which is a separate consideration from insulin dosing.
What fluids should be recommended during sick days?
Sugar-containing fluids are appropriate if oral intake is poor and glucose is not elevated, to prevent hypoglycaemia and support hydration. Sugar-free fluids are preferred once glucose is already high.