Sick day insulin: should I increase, reduce, or skip?

First, the most important rule

If you have type 1 diabetes, do not stop insulin on sick days:

When you are sick, stress hormones push sugar up and can quickly lead to ketones and diabetic ketoacidosis (DKA) if insulin is missed.

School and home sick‑day plans from ADA and major diabetes centers clearly advise continuing basal insulin and checking ketones with high sugars during illness.

This principle also applies to many people with insulin‑treated type 2 diabetes: completely skipping insulin can be dangerous.

What to do on a sick day (step by step)

Step 1: Check sugar more often

• Check blood glucose every 2 to 4 hours while sick (including at night if you are significantly unwell), or more often if readings are changing quickly.​
• If you use CGM, still confirm unexpected readings with a finger‑stick if values look wrong or symptoms don’t match.

Many pediatric and adult sick‑day plans recommend frequent checks to catch both highs and lows early.

Step 2: Check ketones if sugars are high or you feel very unwell

Check blood or urine ketones if:

• Blood glucose stays high (commonly above ~250-300 mg/dL, depending on your personal plan) or.
• You have vomiting, abdominal pain, fast breathing, or marked weakness.

High ketones plus high glucose can signal developing DKA, which needs urgent action (extra insulin, fluids, and sometimes hospital care).

Step 3: Fluids are treatment

Your body needs plenty of fluid on sick days to help clear excess sugar and ketones and prevent dehydration:

• If sugars are high: focus on sugar‑free fluids - water, clear soups, sugar‑free electrolyte drinks as advised.
• If sugars are low or trending low and you cannot eat solids: use carbohydrate‑containing fluids (for example, small measured amounts of juice, regular oral rehydration solution, or glucose drinks) as outlined in your sick‑day plan.

Small, frequent sips are often easier to tolerate if there is nausea.

Step 4: Insulin decision

If sugars are high

• You often need extra “correction” insulin, even if you are eating less.
• Many sick‑day plans advise additional rapid‑ or short‑acting insulin based on:

  • Your usual correction factor, or.

  • A preset sliding scale your doctor gave you.

If sugars are low

• You usually still need your background (basal) insulin to:

  • Prevent ketones.

  • Cover baseline glucose output from the liver.
• Mealtime (bolus) insulin doses may be reduced or held depending on how much carbohydrate you are actually taking in (solids and liquids).
• This should follow your personal sick‑day plan made with your diabetes team; never guess large changes without guidance.

In summary:

• Basal insulin: almost never stopped in type 1, usually continued in insulin‑treated type 2.
• Bolus insulin: adjusted to actual carb intake, but corrections are often needed if glucose is high.

Step 5: When to seek urgent medical help

Go to emergency care or contact your diabetes team urgently if any of the following occur:

• Moderate or large ketones, or ketones that do not improve after extra insulin and fluids.
• Repeated vomiting or you cannot keep fluids down.
• Fast or deep breathing, chest pain, severe drowsiness, confusion, or severe abdominal pain.
• Blood glucose stays very high despite correction insulin.
• Signs of severe dehydration: very dry mouth, minimal urine, dizziness when standing.

These can be signs of DKA or another serious illness and should not be managed at home alone.

Special notes for type 2 diabetes

Many people with type 2 diabetes ask: “Should I stop tablets when I have fever and I am not eating?”

The safe general principle from UK and other national “sick‑day rules” is:

Some tablets are temporarily stopped during dehydrating illness, but not all, and insulin is often continued with dose adjustment.

Examples commonly included in sick‑day rules:

• Metformin - often paused during significant dehydration, vomiting, or risk of acute kidney injury (to reduce lactic acidosis risk).
• SGLT2 inhibitors - usually stopped during acute illness, dehydration, or surgery because of risk of euglycemic DKA.
• Sulfonylureas - may need to be held or reduced if you are not eating, because they can cause hypoglycemia with poor intake.

If you use insulin for type 2 diabetes:

You may still need insulin on sick days, with dose adjustments guided by glucose readings and your clinician’s plan.

Do not make broad decisions like “stop all tablets” or “stop all insulin” without checking against a written sick‑day plan or speaking to your diabetes team.

A simple takeaway patients remember

• Type 1 diabetes:

  • Do not stop insulin on sick days.

  • Check sugars frequently, check ketones when sugars are high or you feel very sick, drink fluids, and use your correction plan early.
• Type 2 diabetes:

  • Some tablets may be paused during dehydrating illness (metformin, SGLT2 inhibitors, some others), but this must follow sick‑day rules from your clinician, not guesswork.

  • If you are on insulin, you usually still need it, with doses adjusted based on readings.

Sick days need more monitoring and smarter adjustments, not skipping treatment.