A blood sugar reading above 400 mg/dL is considered severe hyperglycemia and signals a critical imbalance in how your body is handling glucose. At this level, your cells are unable to absorb sugar efficiently, often due to insufficient insulin or insulin resistance. When left untreated, this condition can quickly escalate into life-threatening complications such as diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS).
For most people:
- Normal fasting blood sugar: 70–99 mg/dL
- Prediabetes: 100–125 mg/dL
- Diabetes (fasting): 126 mg/dL or higher
- Dangerous level: 300–400+ mg/dL
A reading of 400 or above is not just high — it is dangerous and requires immediate medical attention.
Is Blood Sugar Over 400 a Medical Emergency?
Yes. Blood glucose at this level may indicate your body is entering a crisis state. Without proper insulin, your body begins breaking down fat for energy, producing acids called ketones. High ketone levels lead to DKA, which can cause:
- Dehydration
- Organ failure
- Diabetic coma
- Death
This makes a blood sugar level over 400 an urgent situation that should never be ignored.
Immediate Steps to Take If Your Blood Sugar Is Over 400
1. Stay Calm but Act Quickly
Panic can worsen blood sugar through stress hormones. Stay composed, sit down, and prepare to take action.
2. Recheck Your Blood Sugar
Wash your hands with warm water and soap, dry thoroughly, and retest. False readings can happen due to:
- Dirty fingers
- Expired test strips
- Incorrect meter calibration
- Improper storage of supplies
If the second result still shows above 400 mg/dL, treat it as real and dangerous.
3. Contact Your Doctor or Diabetes Care Team Immediately
Call your healthcare provider and report:
- Your current blood sugar reading
- Any symptoms you feel
- Medications taken recently
Follow their instructions carefully. They may advise:
- Additional insulin (correction dose)
- Increased hydration
- Urgent ER visit
Check for Ketones Immediately
If your blood sugar exceeds 240 mg/dL, you should test your urine or blood for ketones using home testing strips or a ketone meter.
Why Ketones Matter
High ketones mean your body is breaking down fat due to lack of insulin, indicating possible DKA.
If Ketones Are Present:
- Do NOT exercise
- Drink water
- Go to the emergency room as instructed
Presence of moderate to large ketones combined with high glucose is a medical emergency.
When to Call 911 or Go to the Emergency Room
Seek emergency care immediately if you have high blood sugar along with:
- Rapid or deep breathing
- Fruity-smelling breath
- Severe nausea or vomiting
- Confusion or inability to focus
- Chest pain
- Extreme fatigue
- Severe abdominal pain
- Dry mouth and skin
These are classic symptoms of diabetic ketoacidosis and require urgent treatment.
What Happens If Blood Sugar Over 400 Is Left Untreated?
Long-term or repeated episodes can lead to:
- Diabetic neuropathy (nerve damage)
- Kidney disease or failure
- Vision loss (diabetic retinopathy)
- Heart attack and stroke
- Weakened immune system
- Diabetic coma
Prolonged severe hyperglycemia damages blood vessels and organs, reducing life expectancy significantly.
Common Causes of Blood Sugar Spikes Above 400
Medication-Related
- Missed insulin doses
- Incorrect insulin dosage
- Expired insulin
- Steroids (prednisone)
- Certain antibiotics
Lifestyle Causes
- Overeating carbohydrates
- Sugary drinks
- Lack of physical activity
- Dehydration
- Emotional or physical stress
- Poor sleep
Medical Conditions
- Infections
- Illness or fever
- Hormonal disorders
- Pancreatic problems
How to Lower Blood Sugar Safely After a Spike
✅ Follow Doctor Instructions
Only take correction insulin as prescribed.
✅ Hydrate Aggressively
Drink water every 15–30 minutes unless restricted.
✅ Rest
Avoid strenuous activity if ketones are present.
✅ Monitor Every 1–2 Hours
Track readings to ensure levels are decreasing.
Natural Ways to Prevent Blood Sugar Over 400
1. Eat Low-Glycemic Foods
Choose:
- Leafy greens
- Whole grains
- Lentils and beans
- Nuts and seeds
- Lean proteins
Avoid:
- Sodas
- Candy
- White bread
- Pastries
2. Follow the Plate Method
- 50% vegetables
- 25% protein
- 25% complex carbs
3. Exercise Regularly
Aim for 150 minutes of moderate activity per week. Walking after meals helps significantly.
4. Prioritize Sleep
Poor sleep increases insulin resistance and glucose levels.
5. Manage Stress
Use meditation, breathing exercises, or yoga to reduce cortisol spikes.
Best Supplements That May Help Control Blood Sugar
(Always consult your doctor first)
- Chromium
- Magnesium
- Alpha-lipoic acid
- Berberine
- Cinnamon extract
- Vitamin D
Monitoring Tips for Better Control
- Check fasting glucose daily
- Monitor post-meal levels
- Use continuous glucose monitors if available
- Keep a blood sugar log
Frequently Asked Questions
At what blood sugar level does a diabetic coma occur?
Typically above 600 mg/dL combined with dehydration and ketones.
Should I take insulin if my blood sugar is over 400?
Only if prescribed and instructed by your doctor.
How long does it take for blood sugar to drop?
With treatment, levels may drop within 2–6 hours, depending on severity.
Can stress alone cause blood sugar over 400?
Stress can contribute but rarely causes levels this high alone.
Difference Between DKA and HHS
| Condition | Common In | Blood Sugar Level | Ketones |
|---|---|---|---|
| DKA | Type 1 Diabetes | 300–600 | High |
| HHS | Type 2 Diabetes | 600+ | Low/None |
Both are medical emergencies.
Emergency Checklist for Blood Sugar Over 400
- ✅ Recheck glucose
- ✅ Drink water
- ✅ Test for ketones
- ✅ Call doctor
- ✅ Monitor symptoms
- ✅ Seek ER care if symptoms worsen
Long-Term Strategy for Preventing Severe Hyperglycemia
- Regular A1C testing
- Medication adherence
- Diabetes education
- Diet planning
- Routine physical activity
- Continuous monitoring
The Takeaway
A blood sugar level over 400 mg/dL is a serious medical condition that should never be ignored. Immediate action, medical intervention, and careful monitoring are essential to prevent life-threatening complications such as diabetic ketoacidosis or diabetic coma. With early response and proper lifestyle management, severe hyperglycemia can be controlled and prevented in the future.