Blood sugar below 70 mg/dL (3.9 mmol/L) is considered dangerously low and requires prompt treatment, while readings above 240 to 250 mg/dL (13.3 to 13.9 mmol/L) become concerning when accompanied by illness or other warning signs. However, there is no single dangerous blood sugar level that applies to everyone. The seriousness of any reading depends on the actual number, your symptoms, ketone levels, how long the elevation lasts, your medications, and your personal diabetes management plan.

What Blood Sugar Levels Mean for Your Health?

Understanding your glucose targets is the foundation of safe diabetes management. For most nonpregnant adults with diabetes, healthcare providers recommend keeping blood sugar between 70 and 180 mg/dL throughout the day. Before meals, the target is typically 80 to 130 mg/dL, and about two hours after eating, it should stay below 180 mg/dL.

These targets may shift based on your age, whether you are pregnant, your diabetes type, the medications you take, other health conditions, and your risk of experiencing dangerously low blood sugar. Children, pregnant people, and older adults often have different target ranges than the general adult population.

A single elevated reading is not automatically an emergency. For example, a fasting glucose level of 126 mg/dL meets the diagnostic threshold for diabetes, but it is not usually an immediately dangerous reading. However, patterns matter. If you repeatedly see readings above 200 mg/dL, especially with symptoms like excessive thirst, frequent urination, blurred vision, fatigue, or unexplained weight loss, contact your healthcare provider.

How to Recognize and Treat Dangerously Low Blood Sugar?

Hypoglycemia, or low blood sugar, occurs when glucose falls below 70 mg/dL. At this level, your blood sugar may continue to drop, so immediate treatment is essential. A reading below 55 mg/dL is considered severely low and poses serious risks. When blood sugar drops this far, your brain may not receive enough glucose to function normally, leading to confusion, loss of coordination, seizures, fainting, or an inability to treat yourself.

The warning signs of low blood sugar include shaking or trembling, sweating, hunger, a fast heartbeat, dizziness, anxiety, irritability, headache, blurred vision, weakness, and confusion. As glucose continues to fall, you may have difficulty speaking clearly or walking normally. In severe cases, hypoglycemia can cause unusual behavior, loss of consciousness, seizures, coma, and in rare instances, death.

Some people experience severe symptoms at higher readings, while others may have few warning signs despite dangerously low blood sugar. This condition, called hypoglycemia unawareness, makes it especially important to check your glucose regularly.

• Common Causes: Taking too much insulin, taking certain diabetes medicines, missing or delaying a meal, eating fewer carbohydrates than expected, exercising more than usual, drinking alcohol without enough food, having kidney or liver disease, or becoming ill and losing your appetite.
• Schedule Changes: Changing your medication schedule, diet, or physical activity without adjusting your diabetes plan can increase hypoglycemia risk.
• Immediate Treatment: If you are conscious and can swallow safely, follow the 15-15 rule: consume 15 grams of fast-acting carbohydrates, wait 15 minutes, check your glucose again, and repeat if it remains below 70 mg/dL.

Fast-acting carbohydrate options include glucose tablets, glucose gel, four ounces of fruit juice, regular soda, or one tablespoon of sugar or honey. Avoid chocolate and high-fat foods because fat may slow glucose absorption.

If you are unconscious, having a seizure, or unable to swallow, do not give food or drink by mouth. Instead, administer glucagon if you have it prescribed and call emergency services immediately.

When Does High Blood Sugar Become a Medical Emergency?

High blood sugar above 180 mg/dL, especially when measured about two hours after eating, requires attention, particularly if the elevation is repeated or rising. A reading of 240 to 250 mg/dL or higher becomes more concerning when you are ill or have ketones present in your blood or urine. People with diabetes may be advised to test for ketones at this level and follow their sick-day management plan.

Blood glucose around 600 mg/dL or higher may indicate a life-threatening condition called hyperosmolar hyperglycemic state (HHS). This emergency causes severe dehydration and changes in brain function and requires immediate hospital care.

Early symptoms of high blood sugar include increased thirst, frequent urination, dry mouth, blurred vision, headache, fatigue, weakness, and unexplained weight loss. As glucose continues to rise, you may develop severe dehydration, nausea, confusion, drowsiness, seizures, or loss of consciousness.

Some people with long-standing type 2 diabetes may have dangerously high blood sugar without obvious symptoms, which is why regular glucose monitoring remains important even when you feel well.

If your blood sugar reads above 300 mg/dL and does not decrease after following your prescribed treatment plan, check for ketones if your healthcare team has instructed you to do so. Contact your provider urgently if the reading persists or occurs with vomiting, abdominal pain, fruity-smelling breath, breathing difficulty, dehydration, or confusion.

A reading over 400 mg/dL is severely elevated and requires prompt action. Wash and dry your hands, repeat the test, check ketones if possible, and follow your healthcare provider's emergency instructions. Seek urgent medical help if the reading remains high or is accompanied by illness, dehydration, vomiting, breathing changes, confusion, or drowsiness.

What New Technology Is Helping Children Monitor Blood Sugar?

In a significant development for pediatric diabetes management, the Food and Drug Administration (FDA) approved the first over-the-counter, integrated continuous glucose monitoring (CGM) device for children on June 12. Dexcom's Stelo Glucose Biosensor received clearance for children ages 2 and older who do not use insulin and do not require a prescription.

The Stelo system consists of a small sensor inserted just under the skin that pairs with a smartphone app. It automatically measures glucose levels continuously, providing a new reading every 15 minutes, allowing users to view patterns and trends throughout the day. Each biosensor can be worn for up to 15 days and is waterproof, working under eight feet of water for up to 24 hours.

The approval is intended for children without diabetes and those with diabetes who use oral medications to manage their condition. Over-the-counter access will help children and youth understand the impact of diet and exercise on their blood sugar levels and may help curb the rising tide of prediabetes and type 2 diabetes in the country. Approximately one in five children in the United States lives with obesity, and rates of both prediabetes and type 2 diabetes are on the rise in this age group.

"Children deserve access to the best tools available to manage their health. Today's clearance reflects the FDA's commitment to fostering innovation for pediatric patients and supporting the safe and effective use of medical devices where children live, learn and play," said Dr. Michelle Tarver, director of the FDA's Center for Devices and Radiological Health.

Dr. Michelle Tarver, Director of the FDA's Center for Devices and Radiological Health

Families with children can use the Stelo to track patterns in response to foods and exercise, helping them make more informed choices and adjustments to their routines to better support healthy lives. Learning how blood sugar responds to food is an important step in assessing insulin sensitivity and resistance and managing other factors associated with prediabetes and type 2 diabetes.

However, the Stelo is not suitable for everyone. This system should not be used by people at risk of severely low blood sugar, such as those who are insulin-dependent, or who have hypoglycemia unawareness, as it lacks the alerts and alarms that prescription CGMs provide. Parents of children with eating disorders or disordered eating should talk with their healthcare team before starting therapy with the Stelo.

The Stelo is now available in pharmacies without requiring a prescription. If you have questions about continuous glucose monitoring or whether it might be appropriate for you or your child, speak with your healthcare team.