High blood sugar (hyperglycemia) often has no symptoms until levels are quite elevated. Knowing the early signs helps you catch problems sooner.
Early symptoms (glucose 180–250 mg/dL)
- Increased thirst
- Frequent urination
- Fatigue, sluggishness
- Mild blurred vision
- Slow-healing cuts or bruises
- Increased appetite despite eating
Moderate symptoms (250–400 mg/dL)
- Persistent headache
- Difficulty concentrating
- Pronounced thirst, dry mouth
- Frequent infections (UTIs, yeast)
- Unintended weight loss
Severe symptoms — call your doctor or go to ER
- Glucose over 400 mg/dL
- Nausea or vomiting
- Fruity-smelling breath (DKA warning)
- Abdominal pain
- Rapid breathing
- Confusion or drowsiness
- Loss of consciousness
When to test
Test if you experience: - Two or more early symptoms - Recent illness or steroid use - Major dietary change - New medication
Common causes of unexpected highs
- Illness or infection
- Stress
- Steroid medications
- Skipped diabetes medications
- Larger portions than estimated
- Dehydration
- Poor sleep
When to call your doctor
- Glucose over 240 mg/dL for more than 24 hours
- Glucose over 300 mg/dL on any reading
- Ketones in urine
- Any severe symptom
Hyperglycemia handled promptly is manageable. Ignored, it leads to DKA or HHS — both life-threatening emergencies.