Situation: A 24-year-old woman with type 1 diabetes mellitus uses insulin glargine at bedtime and insulin lispro with meals. Her written plan calls for 1 unit of lispro for every 10 g of carbohydrate in a meal, plus a correction of 1 unit for every 50 mg/dL (2.8 mmol/L) that her premeal glucose is above 150 mg/dL (8.3 mmol/L). Months later she calls the clinic on the first day of a stomach illness. She has vomited twice, is eating very little, and her glucose is 265 mg/dL (14.7 mmol/L). According to sick-day rules, what should the nurse tell her?

On sick days basal insulin is never stopped, because illness raises glucose and missing insulin in type 1 diabetes leads to ketoacidosis. Glucose is checked every 2–4 hours and ketones whenever glucose is above 240 mg/dL (13.3 mmol/L). She should keep taking fluids and call the provider because she is vomiting.

Core answer

The correct instruction is to continue the usual basal insulin glargine and check for ketones now. On a sick day, basal insulin is never omitted, because acute illness raises counter-regulatory hormones and glucose, and withholding insulin in type 1 diabetes rapidly leads to diabetic ketoacidosis (DKA).

Why basal insulin must continue

Illness such as vomiting and poor oral intake does not reduce the need for basal insulin. Fever, infection, dehydration, and stress hormones such as cortisol, glucagon, and catecholamines increase hepatic glucose output and insulin resistance. In type 1 diabetes, an absolute or relative insulin deficiency is the central driver of DKA . Even when the patient is eating very little, basal glargine must be continued to suppress lipolysis and ketogenesis. Stopping glargine because the patient cannot eat is a dangerous error that converts a simple sick day into ketoacidosis.

Why ketones are checked now

The patient’s glucose is 265 mg/dL (14.7 mmol/L), which is above the sick-day threshold of 240 mg/dL (13.3 mmol/L) for ketone testing. DKA is classically diagnosed by the triad of hyperglycemia, metabolic acidosis, and ketonemia; hyperglycemia in DKA is typically greater than 250 mg/dL . Nausea and vomiting are common early symptoms of DKA , so gastrointestinal symptoms in a patient with type 1 diabetes must not be dismissed as a simple stomach illness. The combination of vomiting, poor intake, and glucose above 240 mg/dL requires immediate urine or blood ketone measurement.

Why the other options are unsafe

Option	Problem
1. Check ketones only once glucose passes 300 mg/dL	The sick-day threshold is 240 mg/dL, not 300 mg/dL. Delaying ketone testing allows early DKA to progress.
3. Stop drinking fluids until vomiting settles	Dehydration worsens hyperglycemia and accelerates DKA. Small, frequent sips of fluid should continue unless the provider advises otherwise.
4. Skip glargine until she can eat full meals	Omitting basal insulin during illness precipitates ketoacidosis. Basal insulin is never stopped on sick days.

Clinical reasoning for the nurse

The patient has two vomiting episodes and is eating very little, yet her glucose is 265 mg/dL. This is not a simple fasting state; it reflects the catabolic, insulin-resistant state of acute illness. The priority is to preserve basal insulin action and detect ketosis early, before acidosis becomes symptomatic. Gastrointestinal symptoms such as nausea, vomiting, and abdominal pain can be misdiagnosed as a routine stomach illness even when ketoacidosis is developing, especially when hyperglycemia is only mild to moderate . Therefore, the nurse should instruct the patient to take her usual glargine dose, check ketones immediately, monitor glucose every 2–4 hours, continue small sips of fluid, and contact the provider because she is vomiting.

Watch out! Vomiting in type 1 diabetes is a red flag for DKA, not a reason to hold insulin. Key point! Basal insulin is continued on sick days; ketones are checked whenever glucose is above 240 mg/dL.