What Blood Sugar Level Is Dangerous?
A Doctor’s Guide to High and Low Glucose Levels

Educational information written by Dr. Albana Greca, MD, Family Physician & General Practitioner,

Medically reviewed by Dr. Ruden Cakani, Endocrinologist

Last reviewed: January 2026

Blood sugar (glucose) levels that are too high or too low can rapidly affect your health. Understanding when your numbers may be dangerous, what symptoms to watch for, and when to act can help prevent serious complications.

This guide explains key ranges, symptoms, and practical next steps you can take.

What Blood Sugar Level Is Dangerous?

A blood sugar level becomes dangerous when it is:

• Low enough to impair brain function, or
• High enough to cause acute complications such as dehydration, diabetic ketoacidosis (DKA), or hyperosmolar hyperglycemic state (HHS).

Danger is not defined by a number alone. Symptoms, how quickly levels change, illness, medications, and individual health factors all matter.

🚨 Seek Emergency Care Immediately If

• Blood sugar stays above 300 mg/dL (16.7 mmol/L) and does not come down
• You have vomiting, abdominal pain, or rapid/deep breathing
• You feel confused, drowsy, or unable to stay awake
• Ketones are positive in urine or blood
• Blood sugar rises above 600 mg/dL (33.3 mmol/L)
• There is loss of consciousness or seizures

Dangerous Low Blood Sugar Levels (Hypoglycemia)

Low blood sugar becomes dangerous when the brain does not receive enough glucose.

Symptoms of Dangerous Low Blood Sugar

• Shaking, sweating, anxiety
• Sudden confusion or difficulty speaking
• Blurred vision
• Weakness or dizziness
• Loss of consciousness or seizures (severe cases)

When Is Low Blood Sugar an Emergency?

• Below 70 mg/dL (3.9 mmol/L): Treat immediately
• Below 54 mg/dL (3.0 mmol/L): Clinically significant and dangerous
• Unconsciousness or seizures: Call emergency services

What Blood Sugar Level Is Dangerously High?

High blood sugar becomes dangerous when it persists or is accompanied by symptoms.

Warning Signs of Dangerous High Blood Sugar

• Extreme thirst
• Frequent urination
• Dry mouth or skin
• Fatigue or weakness
• Blurred vision

What Are Ketones, and Why Do They Matter?

Ketones appear when the body lacks enough insulin and begins breaking down fat for energy.
Moderate or high ketones together with high blood sugar may indicate diabetic ketoacidosis (DKA), a medical emergency.

You should check ketones if:

• Blood sugar is above 240 mg/dL (13.3 mmol/L)
• You are sick, dehydrated, or not eating normally
• You feel nauseated or have abdominal pain

Positive ketones mean your body is lacking insulin, and urgent medical advice is needed.

What to Do If Your Blood Sugar Is Dangerous?

If Blood Sugar Is Low

Use the 15–15 rule:

• Take 15 g of fast-acting carbohydrate
• Recheck blood sugar after 15 minutes
• Repeat if still low

Once stable, eat a balanced snack if advised by your healthcare provider.

If Blood Sugar Is High

• Drink water
• Follow your personal correction plan
• Do NOT exercise if ketones are present
• Seek medical advice if levels do not improve

Never take extra insulin unless it is part of a written correction plan provided by your healthcare provider.

When to Go to the Hospital for Blood Sugar Levels?

Please seek emergency care right away if:

• Blood sugar is extremely high and not falling
• You have persistent vomiting
• You feel confused or cannot stay awake
• Breathing becomes rapid or deep
• You cannot keep fluids down

Frequently Asked Questions

Take-Home Tips

• Monitor blood sugar regularly and watch for patterns

• Avoid intense exercise during illness or when ketones are present

• Limit alcohol, as it increases hypoglycemia risk

• Ask your doctor to adjust medications if lows or highs occur

• Have an emergency plan for both high and low blood sugar

References:

• Kids too high blood sugar
• Blood Sugar Targets
• Hypoglycemia classification—ADA
• Too Low Blood Sugar Self Care
• General Clinical Guidance on DKA and HHS

Final Note

Managing blood sugar safely is not about perfection — it is about recognition, timely action, and prevention.

When in doubt, it is always safer to seek medical advice early.

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Disclaimer

The information provided on www.all-about-beating-diabetes.com is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult with your doctor or qualified healthcare provider before making any changes to your treatment plan, especially before using any supplements, herbs, or alternative remedies. Your health and safety come first.

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