High Blood Sugar
Know the Signs of a Dangerous Crisis
General information from an emergency physician. It adds to your discharge papers and does not replace them or your own doctor. What this site is and isn’t
Key Takeaways:
- High blood sugar can range from a number to manage to a true emergency.
- If you use basal insulin, illness is not a reason to stop it.
- Vomiting, ketones, deep breathing, or confusion need immediate care.
About Your Diagnosis & ED Workup
Insulin helps sugar enter cells. Sometimes the body resists insulin. Sometimes there is too little insulin. Then sugar builds up in the blood. The cells cannot use it normally.
When blood sugar rises above roughly 180 to 200 mg/dL, sugar spills into urine. It pulls water and salts with it. This causes frequent urination, thirst, and dehydration.
The emergency evaluation looks for two dangerous problems. One is diabetic ketoacidosis, called DKA. The other is hyperosmolar hyperglycemic state, called HHS. Acid, ketones, dehydration, and alertness matter. Glucose alone does not tell the whole story.
First Steps & Evidence-Based Home Care
Follow your diabetes sick-day plan. Check glucose every 2 to 4 hours while ill. Check ketones when glucose is above 200 mg/dL. Also check them when you are sick.
Never omit basal insulin because you are sick or not eating. Any dose change is an individual clinical decision.
Keep taking fluids and carbohydrates as directed by the sick-day plan.
Tell the follow-up team if insulin costs make you stretch or skip doses. Rationing insulin causes DKA.
Timeline & Expected Recovery Course
High blood sugar does not always require a hospital stay. This may be safe when there is no dangerous acid, ketone, dehydration, alertness, or trigger problem.
DKA can develop over hours. Feeling well or seeing a lower glucose number does not exclude it, especially with an SGLT2 inhibitor.
High sugar commonly returns if the infection, missed insulin, medicine problem, or other trigger is not corrected.
Emergency Red Flags (When to Return Immediately)
Return to the emergency department for any of these. This list is not exhaustive.
- Vomiting that continues or being unable to keep fluids down.
- Glucose above 300 mg/dL despite insulin.
- Blood ketones at least 1.5 or large urine ketones that are not improving.
- Rapid, deep breathing; abdominal pain; nausea; or fruity breath.
- Confusion, extreme sleepiness, severe dehydration, or fever with uncontrolled sugar.
If you take an SGLT2 inhibitor, watch for nausea, vomiting, or belly pain. These may be DKA even when glucose is below 200.
Reviewed September 3, 2026