Adjusting Insulin for Illness: Sick-Day Rules for Basal, Bolus, and Correction Doses

Why Illness Raises Blood Glucose Even When You Stop Eating

The body's stress response is the problem. Illness triggers the release of cortisol, epinephrine, glucagon, and growth hormone. These counter-regulatory hormones stimulate hepatic glucose production and simultaneously blunt peripheral insulin sensitivity, a combination that sends blood glucose climbing regardless of what you eat or do not eat. A 2014 analysis published in Diabetes Care confirmed that infection was the precipitating factor in 30 to 40% of all diabetic ketoacidosis (DKA) admissions in the United States, underscoring how reliably illness destabilizes glucose control [1].

Cortisol alone can increase hepatic glucose output by 2 to 3 mg/kg/min above baseline. For a 70-kg adult, that translates to roughly 140 mg/min of additional glucose flooding the circulation. No amount of appetite suppression compensates for that output when insulin doses remain unchanged.

The practical upshot: expect blood glucose to be higher than usual during any fever, respiratory infection, gastrointestinal illness, urinary tract infection, or surgical procedure. Planning ahead, not reacting after the fact, is what prevents hospitalization.

Basal Insulin: The Non-Negotiable Anchor

Basal insulin should not be stopped during illness, even if you cannot eat a single bite. This is the single most repeated instruction in diabetes sick-day guidance, and it remains the most frequently ignored. The American Diabetes Association's 2024 Standards of Care state explicitly that "patients should be instructed never to omit insulin during illness" [2].

Basal insulin covers the glucose your liver continuously releases between meals. That hepatic output does not pause because you have the flu. It accelerates. Stopping glargine (Lantus, Basaglar, Toujeo), detemir (Levemir), or degludec (Tresiba) during illness removes the only brake on that output and is a direct path to DKA in type 1 diabetes and to severe hyperglycemia in insulin-dependent type 2 diabetes.

If your usual basal dose was working well before illness, maintain the full dose. If blood glucose has been running below 100 mg/dL despite illness (rare, but possible with severe vomiting and no oral intake), a 10 to 20% temporary reduction with close monitoring every two hours is a reasonable short-term adjustment. Do not reduce by more than 20% without speaking to your provider.

For patients on an insulin pump (continuous subcutaneous insulin infusion, CSII), a temporary basal rate increase of 20 to 40% is standard practice during febrile illness, and the pump's capability to make precise fractional adjustments makes this safer than it sounds. A 2020 study in Diabetes Technology and Therapeutics (N=214 type 1 adults) found that pump users who increased temporary basal rates during illness spent 18% more time in range (70 to 180 mg/dL) on sick days compared to those who made no basal adjustments [3].

Understanding the Basal-Bolus Framework Before You Modify It

Adjusting insulin safely during illness requires a working understanding of the basal-bolus system. Basal insulin (long-acting) suppresses fasting hepatic glucose production around the clock. Bolus insulin (rapid-acting: lispro/Humalog, aspart/NovoLog, glulisine/Apidra, or the ultra-rapid fiasp) covers glucose from meals and corrects existing hyperglycemia.

Two ratios govern bolus dosing: the insulin-to-carbohydrate ratio (ICR) and the correction factor (also called insulin sensitivity factor, ISF).

Insulin-to-carbohydrate ratio tells you how many grams of carbohydrate one unit of rapid-acting insulin covers. A ratio of 1:15 means one unit covers 15 grams. The standard starting estimate uses the "500 rule": divide 500 by the patient's total daily insulin dose (TDD). A person taking 50 units per day would start with an ICR of 1:10 (500 ÷ 50 = 10). The ADA and the American Association of Clinical Endocrinology both endorse this formula as an initial approximation, with subsequent fine-tuning based on two-hour postprandial glucose [4].

Correction factor (ISF) tells you how far blood glucose drops per unit of rapid-acting insulin. The "1,700 rule" (sometimes called the "100 rule" for regular human insulin) divides 1,700 by TDD. Using the same 50-unit example, ISF = 34 mg/dL per unit. So if target glucose is 120 mg/dL and current glucose is 240 mg/dL, the correction dose is (240 - 120) ÷ 34 = approximately 3.5 units.

During illness, both the ICR and ISF shift because insulin resistance increases. The doses needed to achieve the same result go up, often by 20 to 50% across the board.

Calculating and Adjusting Your Correction Factor During Illness

The correction factor is your primary tool for treating hyperglycemia when you are sick and not eating normally. Getting it right matters enormously, because stacking uncorrected doses can cause severe hypoglycemia several hours later.

Start with your pre-illness ISF and apply a 20 to 30% reduction to that number, which reflects the fact that each unit of insulin now has less power. If your usual ISF was 40 mg/dL per unit, illness-adjusted ISF might be 28 to 32 mg/dL per unit, meaning you need more units to achieve the same glucose drop.

The HealthRX Sick-Day Correction Ladder (for clinical review before patient use):

1. Blood glucose 180 to 249 mg/dL: use your standard correction formula with a 20% dose increase. Recheck in 2 hours.
2. Blood glucose 250 to 299 mg/dL: use correction formula with a 30% dose increase. Check ketones. Recheck in 2 hours.
3. Blood glucose 300 to 349 mg/dL: use correction formula with a 40 to 50% dose increase. Check ketones. If ketones are moderate or large, call your provider now.
4. Blood glucose 350 mg/dL or above, or any level with large ketones: call your provider or go to an emergency department.

The two-hour recheck rule is not optional. It prevents both undertreating persistent hyperglycemia and inadvertently stacking doses that cause delayed hypoglycemia.

One more constraint: never give a correction dose sooner than the duration of action of your previous bolus. Lispro, aspart, and glulisine are active for approximately 3 to 4 hours. Fiasp is slightly shorter at roughly 3 hours. Correcting before the previous dose has finished acting is one of the most common causes of hypoglycemia in people managing sick days at home.

Bolus Insulin Adjustments When You Can Still Eat

Many illnesses allow some oral intake, particularly mild upper respiratory infections where appetite is reduced but not absent. In that scenario, the approach is to dose bolus insulin based on what you actually eat, not on what you planned to eat, and then apply the illness-adjusted ICR.

If your normal ICR is 1:10 and illness typically raises your insulin needs by 30%, your sick-day ICR becomes approximately 1:7 (one unit per 7 grams of carbohydrate). Round to the nearest half-unit if your pen or pump allows it.

Practical carbohydrate counting during illness also differs from routine practice. Sick-day foods tend to be simple: crackers, broth-based soup, fruit juice, gelatin, toast, or oral electrolyte solutions. A standard dose of 30 mL of most liquid cold medications contains roughly 3, 5 grams of sugar. This is unlikely to require coverage on its own, but it is worth checking the label when glucose is already high.

The 15-grams-per-hour carbohydrate floor is useful guidance when nausea limits eating: aim to take in at least 15 grams of carbohydrate per hour to prevent starvation ketosis overlapping with insulin-related hypoglycemia [5].

Ketone Monitoring: When and How

Ketone testing is not just a type 1 diabetes task. Anyone on insulin who is ill and has a blood glucose above 250 mg/dL should check ketones. There are two practical options: urine ketone strips (Ketostix and equivalents) and blood ketone meters (measuring beta-hydroxybutyrate directly, with a normal value below 0.6 mmol/L).

Blood ketone meters are more accurate and faster to reflect real-time changes. A 2013 study in Diabetes Care (N=149) showed that blood ketone testing detected DKA-range ketosis an average of 60 minutes earlier than urine strips during acute illness, allowing earlier intervention [6].

Interpretation for urine strips: trace or small ketones with normal glucose require only increased hydration. Moderate ketones (40 mg/dL on the strip) with glucose above 250 mg/dL: contact your provider within two hours. Large ketones (80 mg/dL or above): call your provider or go to the emergency department now.

For blood ketones: values above 1.5 mmol/L combined with blood glucose above 250 mg/dL should trigger immediate provider contact. Values above 3.0 mmol/L indicate probable DKA regardless of glucose level.

Hydration and When to Hold Insulin

Hydration does real metabolic work during illness. Adequate fluid intake dilutes blood glucose, supports renal glucose excretion, and reduces the concentration of ketones in the bloodstream. The ADA recommends a minimum of 240 mL (8 ounces) of sugar-free fluid every hour that you are awake and unable to eat during illness [2].

If vomiting prevents any fluid retention for more than two consecutive hours, intravenous fluid replacement becomes necessary, which means going to urgent care or the emergency department. Home management of DKA is not safe.

One situation where a temporary bolus hold is appropriate: blood glucose is below 100 mg/dL and you cannot eat. In this case, hold the mealtime bolus completely, reduce correction doses conservatively, and treat as a pending hypoglycemia situation. Continue basal insulin at or near full dose. Recheck blood glucose every 30 to 60 minutes until glucose rises above 120 mg/dL or you can eat.

SGLT-2 inhibitors (empagliflozin/Jardiance, dapagliflozin/Farxiga, canagliflozin/Invokana) should generally be held during any significant illness. These drugs increase urinary glucose excretion and raise the risk of euglycemic DKA, meaning DKA can occur with blood glucose in the 150 to 200 mg/dL range, not just above 300 mg/dL. The FDA issued a safety communication in 2015 specifically addressing this euglycemic DKA risk [7].

Type 1 vs. Insulin-Dependent Type 2: Different Risk Profiles

Type 1 diabetes carries the highest DKA risk during illness because there is zero residual beta-cell function. A missed basal dose or an undertreated blood glucose spike during a 24-hour gastroenteritis episode can progress to DKA within 8 to 12 hours in a person with type 1 diabetes. Data from the T1D Exchange registry (N=25,529) showed an annual DKA rate of 8.7% in adults with type 1 diabetes, with infection as the most common precipitant [8].

Insulin-dependent type 2 diabetes presents differently. Most patients retain some endogenous insulin secretion, which blunts (but does not eliminate) DKA risk. However, these patients are at significant risk for hyperosmolar hyperglycemic state (HHS), a condition characterized by extreme hyperglycemia (often exceeding 600 mg/dL), severe dehydration, and altered consciousness without significant ketosis. HHS carries a mortality rate of 5 to 20% compared to 0.5 to 2% for DKA, according to a 2021 review in The New England Journal of Medicine [9].

The clinical implication: aggressive hydration is at least as important as insulin adjustment for insulin-dependent type 2 patients during illness.

Communicating With Your Diabetes Care Team

Your provider should define your sick-day rules in advance, ideally as part of a written sick-day management plan. According to the 2024 ADA Standards of Care, diabetes education should include "sick-day management guidelines, including specific glucose and ketone thresholds that require urgent provider contact" [2]. If you do not have a written plan, that is the first thing to request at your next appointment.

Contact your provider without delay if any of the following occur: blood glucose remains above 300 mg/dL after two correction doses, vomiting or diarrhea persists for more than 6 hours, ketones are moderate or large on two consecutive tests, or you feel confused, have difficulty breathing, or develop abdominal pain. These are warning signs of DKA or HHS, both of which require intravenous treatment in a clinical setting.

Do not wait until morning. Both DKA and HHS can deteriorate from manageable to life-threatening within four to six hours without appropriate treatment.

Sick-Day Rules for Insulin Pump Users

Pump therapy adds flexibility but also adds complexity during illness. The key advantages of CSII during illness are the ability to set precise temporary basal rates and the elimination of injection site variability. The primary risk: pump infusion sets can fail silently, and a patient who is already nauseated may not notice that a site has kinked or that insulin delivery has stopped until blood glucose reaches dangerous levels.

Check infusion site placement and tubing integrity every four hours during illness. If blood glucose rises above 250 mg/dL and does not respond to a pump-delivered correction within 90 minutes, the standard recommendation is to deliver one manual injection via syringe (not the pump) and change the entire infusion set immediately [4].

Pump users should also have a supply of long-acting insulin (glargine or degludec) and rapid-acting insulin in syringes or pens available at home. Pump failure during severe illness, with no backup injection supplies, creates a medical emergency.

Glucagon and Emergency Preparedness

Every person on insulin should have a glucagon rescue kit at home and at least one household member or coworker trained in its use. Nasal glucagon (Baqsimi, 3 mg intranasal) and injectable glucagon kits (GlucaGen, Gvoke) are both FDA-approved for severe hypoglycemia. Baqsimi offers the practical advantage of no reconstitution requirement, which matters significantly when the person administering the dose is panicked [10].

Keep the glucagon kit accessible, not locked in a cabinet. Check the expiration date each time you change clocks for daylight saving time.