At wits end-fasting blood sugar 100 - 400

by Annette
(Deming, NM USA)




QUESTION: I follow a very low-carbohydrate diet and take metformin 850 mg twice daily, Januvia, Tresiba 60 units daily, and Humalog 40 units in the morning. My fasting glucose ranges from the high 100s to 400 mg/dL, and I sometimes wake at 2–3 a.m. with readings in the high 400s. Why is this happening?





Emergency Quick Answer


Repeated glucose readings in the 400s despite insulin require emergency medical assessment now. Wash and dry your hands and repeat the test once with a fresh strip, but do not delay care. Go to the nearest emergency department. Call 911 for vomiting, abdominal pain, rapid or difficult breathing, fruity-smelling breath, confusion, severe weakness, fainting, inability to keep fluids down, or moderate or high ketones.




Answer by Dr. Albana Greca, MD, MMedSc



Hi Annette,



Glucose in the high 400s is not explained by the dawn phenomenon alone and should not be managed by adding a snack, exercising harder, fasting longer, or changing insulin timing at home. Severe hyperglycemia can cause major dehydration and may occur with diabetic ketoacidosis or hyperosmolar hyperglycemic state.



What to Do Now




  1. Seek emergency care now if the repeat reading remains above 400 mg/dL.

  2. Check ketones if supplies are already available, but do not delay leaving to obtain or repeat a test.

  3. Do not exercise. Exercise may worsen severe hyperglycemia when dehydration, ketones, or major insulin deficiency are present.

  4. Do not take repeated extra Humalog or increase Tresiba unless you are following a current written correction plan from your own clinician.

  5. If you are awake and not vomiting, sip water while arranging care unless you have a medical fluid restriction.



Bring your insulin pens or vials, needles, glucose meter, strips, medication list, and recent readings. Review the warning signs on our page about dangerous blood sugar levels.



Why Might Glucose Stay High Despite Insulin?



Possible causes include infection, illness, corticosteroid treatment, dehydration, missed or incorrect doses, expired or heat-damaged insulin, a blocked or faulty pen needle, injecting repeatedly into hard or lumpy tissue, incorrect injection technique, or a major change in insulin needs.



Very high readings can also occur when the current basal and mealtime insulin pattern does not match meals and overnight glucose production. Humalog is rapid-acting insulin normally timed around food, while Tresiba is long-acting basal insulin. Their doses and timing must be reviewed together rather than changing only the bedtime dose.



Could This Be the Dawn Phenomenon?



The dawn phenomenon can raise glucose in the early morning, but readings in the high 400s require evaluation for more serious causes. A normal bedtime reading followed by a gradual overnight rise may suggest insufficient basal coverage or illness. A high bedtime reading that remains high overnight may point to inadequate meal coverage, missed insulin, food intake, or another trigger.



A continuous glucose monitor or structured blood sugar log can help identify the pattern after the immediate emergency has been treated.



Does a Very Low-Carbohydrate Diet Help?



Reducing refined carbohydrates can help some people, but an extreme no-carbohydrate diet is not a treatment for glucose in the 400s. It may make meals difficult to balance and, in someone with severe insulin deficiency, a ketogenic eating pattern may complicate interpretation of ketones.



Do not skip meals while using rapid-acting insulin unless your clinician has given specific instructions. Your diabetes team should match carbohydrate intake, meal timing, Humalog, and basal insulin safely. Our guide to carbohydrates and diabetes explains a more balanced approach.



What Should Be Reviewed After Emergency Care?




  • HbA1c and the full fasting, meal, bedtime, and overnight glucose pattern

  • The exact timing and purpose of the 40-unit Humalog dose

  • Tresiba concentration, injection time, storage, and missed doses

  • Injection sites, needle use, pen function, and technique

  • Kidney and liver function, infection, and medicines that raise glucose

  • Whether CGM, a revised basal-bolus plan, or another treatment would improve safety



Tresiba can be taken once daily in adults, but its dose must be individualized and adjusted gradually. Humalog should be used according to a meal and correction plan. Do not move either insulin to bedtime or change the doses without your prescriber.




Important Safety Note


Call 911 for confusion, fainting, severe drowsiness, repeated vomiting, abdominal pain, rapid breathing, chest pain, inability to drink, fruity-smelling breath, or high ketones. Do not rely on stress reduction, a bedtime snack, herbs, fasting, or exercise when glucose is in the 400s.





Doctor’s Note


A complex regimen containing metformin, Januvia, Tresiba, and a large once-daily Humalog dose needs prompt specialist review when glucose still reaches the high 400s. The priority is emergency assessment now, followed by a written plan for basal insulin, mealtime insulin, corrections, ketone testing, illness, and missed doses.





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, tablets, supplements, diet, or exercise plans without speaking with your healthcare provider.




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Last reviewed: July 2026.




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