What to Do if Your Blood Sugar Is Over 400
Updated on December 3, 2025
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If you have diabetes, keeping your blood sugar (glucose) levels within a healthy range is vital for avoiding certain health complications. The American Diabetes Association (ADA) generally recommends a target blood sugar level of between 80 and 130 mg/dL before meals and below 180 mg/dL two hours after meals.
However, everyone’s target range is different, so it’s important to work with your doctor to set the right goals for you. A blood sugar reading over 400 mg/dL is considered severe hyperglycemia and can be a medical emergency.
If your blood sugar is over 400 mg/dL, here are some steps to take.
What to Do if Your Blood Sugar Is High
A reading this high requires a calm and methodical response to ensure your safety. Follow these immediate steps while you get in touch with your healthcare provider.
Test Your Blood Sugar Again
If you get a reading over 400 mg/dL, recheck your blood sugar to rule out a false reading, especially if you don’t have other symptoms like frequent urination or extreme thirst. An inaccurate result can occur if your hands are not clean, you use expired test strips, or you’ve not kept test strips in the correct storage conditions.
Contact Your Doctor Immediately
If a second test confirms your blood sugar is over 400 mg/dL, call your doctor or endocrinologist right away. Follow the specific treatment plan they have given you for high blood sugar, which may include taking extra insulin or drinking more water, while you wait for their guidance.
Test Your Urine for Ketones
Your doctor may ask you to use a home test strip to check your urine for ketones. High levels of these chemicals are a potential sign of diabetic ketoacidosis (DKA), a life-threatening complication that happens when your body can’t use insulin and starts breaking down fat for energy instead.
The ADA recommends checking for ketones when your blood sugar level is 240 mg/dL or higher.
“In our clinic, if a person has blood sugar levels of over 300 mg/dL, we will check for urine ketones,” says Susan Spratt, MD, an endocrinologist and professor of medicine at Duke University School of Medicine in Durham, North Carolina.
“If their blood sugar levels are over 300 mg/dL — and certainly over 400 mg/dL — we're concerned that they may be going into diabetic ketoacidosis,” says Dr. Spratt.
If ketones are present, your doctor will give you further instructions, which may include going to the emergency room. Do not exercise if you have ketones, as this can make your blood sugar spike even higher.
Know When to Call 911
Untreated hyperglycemia can lead to DKA, which can progress rapidly. According to the Centers for Disease Control and Prevention, you should seek immediate medical help if you experience DKA symptoms like:
- Unusually rapid, deep breathing
- A flushed face
- Breath that has a distinct fruity smell
- Feeling nauseous or vomiting
- Abdominal pain
- A parched mouth and dry skin
- Feeling exhausted
- Headache
- Muscle aches or stiffness
Even if your symptoms aren’t severe, untreated hyperglycemia can cause long-term complications, including nerve damage (diabetic neuropathy), eye damage (diabetic retinopathy), and kidney or heart problems.
Without immediate treatment, DKA can lead to diabetic coma and death. Diabetes is the seventh leading cause of death in the United States, so getting medical care right away is critical if you have symptoms of DKA.
Common Causes of High Blood Sugar
Several factors can cause your blood sugar to spike (or swing) when you have diabetes. Common causes include:
- Not taking the correct dose of your insulin or other diabetes medications
- An imbalance between your carbohydrate intake and your insulin dosage
- Being less physically active than usual
- Experiencing physical or emotional stress
- Taking certain other medications, such as steroids or beta-blockers
How to Help Prevent High Blood Sugar
Following your doctor’s recommendations and taking your medication as prescribed is the most important part of managing your blood sugar. You can also incorporate these habits to help prevent hyperglycemia:
- Limit sugary drinks. Beverages like soda, juice, sweet tea, and sports drinks can raise your blood sugar quickly. Water is the best choice to stay hydrated.
- Choose nutrient-dense carbohydrates. Opt for high-fiber carbs that your body breaks down more slowly, such as beans, berries, sweet potatoes, and whole grains.
- Eat balanced meals. Pairing complex carbs with a lean source of protein and non-starchy vegetables (like broccoli or green beans) can help keep your blood sugar more stable.
- Exercise regularly. The ADA recommends aiming for 150 minutes of moderate-intensity aerobic exercise, like walking, each week.
- Manage stress. Because stress can affect your blood sugar levels, finding healthy coping mechanisms is important.
- Monitor your blood sugar. Check your levels regularly as recommended by your doctor, especially before and after meals, or when you’re feeling symptoms.
- Quit smoking. Nicotine makes it harder for your body to use insulin properly, which can lead to higher blood sugar levels.
The Takeaway
- Healthcare professionals consider a blood glucose reading over 400 mg/dL to be severe hyperglycemia and recommend calling your doctor immediately for guidance.
- Make sure you retest severely high blood glucose readings for accuracy, as several different factors may affect the reading.
- High blood sugar can lead to a life-threatening condition called diabetic ketoacidosis, so call 911 or seek immediate medical attention if you test positive for ketones and have symptoms like fruity-smelling breath, severe stomach pain, or difficulty breathing.
- You can help prevent severe high blood sugar by following the diabetes care plan you created with your doctor, including taking your medication as prescribed, monitoring your blood sugar levels regularly, eating a balanced diet, and engaging in regular exercise.
Common Questions & Answers
At what blood sugar level can a diabetic coma occur?
A blood sugar level above 600 mg/dL can lead to a serious condition called hyperosmolar hyperglycemic state, which can result in a diabetic coma. A diabetic coma is a life-threatening emergency where you are alive but can’t wake up. Following your diabetes care plan is the best way to prevent your blood sugar from reaching such dangerous levels.
Should I take insulin if my blood sugar is over 400?
Blood sugar levels above 300 mg/dL mean you should check your ketones and make immediate contact with your physician. You may need to receive insulin therapy as an intravenous drip to correct both your blood glucose level and the buildup of ketones.
How long does it take for blood sugar to go down?
In a healthy individual, blood sugar usually returns to normal about one to two hours after eating. With type 2 diabetes, this varies depending on the disease progression, the type of insulin you take, and how high your blood glucose levels are.
Resources We Trust
- Mayo Clinic: Diabetes
- Cleveland Clinic: Hyperglycemia (High Blood Sugar)
- Centers for Disease Control and Prevention: Diabetic Ketoacidosis
- American Diabetes Association: Diabetes-Friendly Recipes
- National Institute of Diabetes and Digestive and Kidney Diseases: Diabetes Tests and Diagnosis
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
- Check Your Blood Glucose: Diabetes Testing and Monitoring. American Diabetes Association.
- About Hyperglycemia (High Blood Sugar). Memorial Sloan Kettering Cancer Center. November 14, 2023.
- Hyperglycemia (High Blood Glucose). American Diabetes Association.
- Blood Glucose Monitors: What Factors Affect Accuracy? Mayo Clinic. December 15, 2023.
- Diabetes and DKA (Ketoacidosis). American Diabetes Association.
- Diabetic Ketoacidosis. Centers for Disease Control and Prevention. May 15, 2024.
- Mouri M et al. Hyperglycemia. StatPearls. April 24, 2023.
- Diabetes. Office of Disease Prevention and Health Promotion.
- 10 Surprising Things That Can Spike Your Blood Sugar. Centers for Disease Control and Prevention. May 15, 2024.
- Understanding Carbs. American Diabetes Association.
- Weekly Exercise Targets. American Diabetes Association.
- Diabetes and Smoking. Centers for Disease Control and Prevention. May 15, 2024.
Meet Our Experts
Anna L. Goldman, MD
Medical Reviewer
Anna L. Goldman, MD, is a board-certified endocrinologist. She teaches first year medical students at Harvard Medical School and practices general endocrinology in Boston.
Dr. Goldman attended college at Wesleyan University and then completed her residency at Icahn School of Medicine at Mount Sinai Hospital in New York City, where she was also a chief resident. She moved to Boston to do her fellowship in endocrinology at Brigham and Women's Hospital. She joined the faculty after graduation and served as the associate program director for the fellowship program for a number of years.
Maria Masters
Author
Maria Masters is a contributing editor and writer for Everyday Health and What to Expect, and she has held positions at Men's Health and Family Circle. Her work has appeared in Health, on Prevention.com, on MensJournal.com, and in HGTV Magazine, among numerous other print and digital publications.