High blood sugar, or hyperglycemia, can feel different from person to person. Some people notice symptoms only when glucose is quite high. Others have few symptoms even when numbers are above target.
Quick summary
Common symptoms can include increased thirst, frequent urination, fatigue, blurry vision, headache, dry mouth, slow-healing cuts, and more infections.
Key takeaways
- Symptoms do not always match the glucose number.
- Checking glucose is the only way to know the number at that moment.
- Illness, missed medicine, stress, steroids, food changes, and pump or infusion-set problems can raise glucose.
- Very high glucose with vomiting, dehydration, confusion, or ketones can be urgent.
What to do with a high reading
Follow the plan your clinician gave you. That may include fluids, rechecking glucose, checking ketones, reviewing medicine timing, or using a correction dose if that is already part of your written plan.
Do not give extra insulin or change medicines without a plan. If you do not know what to do with repeated highs, call your care team.
When to seek urgent help
- Vomiting or inability to keep fluids down.
- Moderate or large ketones, if your plan says to check.
- Deep or rapid breathing, fruity breath, confusion, or severe weakness.
- Very high glucose that does not improve with your plan.
- Signs of dehydration or symptoms that feel dangerous.
Practical takeaway
A high number is a signal to follow your plan, look for a cause, and know when to get help.
Safety note
This article is not a substitute for medical care. Seek urgent care for possible DKA or severe dehydration, especially with vomiting, confusion, rapid breathing, or ketones.
What to ask your care team
- What high-glucose number should make me call?
- Should I check ketones?
- Do I have a written correction or sick-day plan?
Related reading
Source summary
- Symptoms of Diabetes, Centers for Disease Control and Prevention. Patient guidance. Accessed June 5, 2026. Source
- Managing Diabetes, National Institute of Diabetes and Digestive and Kidney Diseases. Patient guidance. Accessed June 5, 2026. Source
- Diabetic Ketoacidosis, National Institute of Diabetes and Digestive and Kidney Diseases. Patient guidance. Accessed June 5, 2026. Source
- Diabetes Testing, Centers for Disease Control and Prevention. Patient guidance. Accessed June 5, 2026. Source