Blood sugar still high after insulin, reaching 400 and 500 mg/dL
by Anonymous
(San Francisco,Ca)
QUESTION: I take Humulin R and Novolin N as directed, but for the last week my blood sugar has remained in the 400s and 500s. I am sweating, and my eyes are unusually red and bloodshot. It feels as though the insulin is not working. What should I do?
Emergency Quick Answer
Blood glucose repeatedly in the 400s–500s despite insulin is a medical emergency. Go to the nearest emergency department now. Call 911 if you are confused, very weak, faint, vomiting, unable to keep fluids down, breathing rapidly or with difficulty, or have abdominal pain or fruity-smelling breath. Do not wait for more readings, an office appointment, or an online reply.
Answer by Dr. Albana Greca, MD, MMedSc
Hi,
Readings of 400–500 mg/dL can occur with diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic state (HHS), severe dehydration, infection, or another urgent problem. Both DKA and HHS can become life-threatening and require laboratory testing, intravenous fluids, electrolytes, insulin, and treatment of the underlying cause.
What to Do Right Now
- Arrange emergency care immediately. Do not drive yourself if you feel weak, dizzy, confused, sleepy, or have blurred vision.
- Check ketones if supplies are already available, but do not delay leaving for the hospital. Moderate or high ketones require emergency care.
- Do not exercise. Activity can worsen severe hyperglycemia when insulin deficiency, dehydration, or ketones are present.
- Do not take repeated extra insulin doses unless you are following a written correction plan from your own diabetes clinician. Insulin can overlap and cause a dangerous delayed low.
- If you are awake and not vomiting, sip water while arranging care unless you have been told to restrict fluids. Avoid juice, regular soda, and energy drinks.
Bring your insulin, syringes or pens, glucose meter, strips, medication list, and glucose record to the hospital. Our guide to dangerous blood sugar levels explains the warning signs of a hyperglycemic crisis.
Why Might Insulin Seem Not to Work?
Possible causes include infection, fever, missed or incorrect doses, corticosteroids or another medicine that raises glucose, expired or heat-damaged insulin, incorrect storage, injection into repeatedly used lumpy areas, an incorrect syringe or dose, or a problem preparing or administering the insulin.
Humulin R should be clear and colorless. Novolin N is a suspension that should appear uniformly white and cloudy after it is gently resuspended according to its instructions. Insulin that has frozen, overheated, expired, or looks abnormal should not be used. However, checking these details at home must not delay emergency treatment.
Could an Infection Be Responsible?
Yes. Infection and other acute illnesses increase stress hormones, which can make the body more resistant to insulin. Sweating may occur with fever, infection, dehydration, pain, or other medical problems. Red or bloodshot eyes are not a reliable sign that insulin has failed and also need examination, especially if there is eye pain, discharge, light sensitivity, headache, or a change in vision.
What Will the Medical Team Check?
Clinicians may check blood glucose, ketones, electrolytes, kidney function, blood acidity, hydration, infection, heart status, and whether the insulin was stored and administered correctly. They can then give a safe insulin and fluid plan. Learn more about hyperosmolar hyperglycemic state and blood sugar over 400 mg/dL.
Important Safety Note
Call 911 for confusion, fainting, severe drowsiness, seizure, repeated vomiting, inability to drink, rapid or difficult breathing, chest pain, one-sided weakness, severe dehydration, fruity-smelling breath, or high ketones. Do not rely on herbs, stress remedies, or extra exercise to treat glucose in the 400s–500s.
Doctor’s Note
The priority is emergency assessment, not collecting more overnight readings or deciding insulin doses online. After the crisis is treated, ask your diabetes team to review your Humulin R and Novolin N schedule, injection technique, storage, expiration dates, injection sites, sick-day rules, ketone testing, and written correction plan. Do not change or stop either insulin without medical instructions.
Educational safety note: This answer is for general diabetes education only. It does not replace personal medical advice, diagnosis, or treatment. Do not start, stop, or change insulin, other medicines, supplements, diet, or exercise plans without speaking with your healthcare provider.
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Related Resources
Last reviewed: July 2026.
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