What Is a Dangerous Blood Sugar Level? A Guide for Persons with Diabetes

17 Sep 2025 By Lesley L. Williams, M.D.

What Is a Dangerous Blood Sugar Level? A Guide for Persons with Diabetes

Managing blood sugar is a critical part of living well with diabetes. Understanding what constitutes a dangerous blood sugar level is essential for preventing complications and maintaining overall health. This guide provides comprehensive information about high and low blood sugar levels, their symptoms, and how to manage them effectively.

Understanding Blood Sugar Levels

Blood sugar levels, also known as blood glucose levels, refer to the amount of glucose in your blood. Glucose comes from the food you eat and serves as the primary source of energy for your body. In individuals without diabetes, the body tightly regulates blood sugar levels through the hormone insulin, produced by the pancreas.

In persons with diabetes, this regulation is impaired. Type 1 diabetes involves the body's inability to produce insulin, while type 2 diabetes is characterized by insulin resistance and insufficient insulin production. Consequently, persons with diabetes must actively manage their blood sugar levels through medication, diet, and exercise to avoid extreme highs and lows.

Normal Blood Sugar Ranges

For persons with diabetes, maintaining blood sugar levels within target ranges is vital. These ranges may vary slightly depending on individual circumstances, but generally accepted targets include:

Fasting Blood Sugar: 80-130 mg/dL (before meals)
Postprandial Blood Sugar: Less than 180 mg/dL (1-2 hours after meals)
HbA1c: Less than 7% (average blood sugar over 2-3 months)

These targets can be personalized in consultation with your healthcare provider.

High Blood Sugar Levels (Hyperglycemia)

Hyperglycemia refers to elevated blood sugar levels. It occurs when the body has too little insulin or when the insulin is not working effectively. Chronic hyperglycemia can lead to serious health problems, including heart disease, kidney disease, nerve damage, and vision problems.

Symptoms of Hyperglycemia

Recognizing the symptoms of hyperglycemia is essential for timely intervention. Common symptoms include:

Frequent Urination: High blood sugar overwhelms the kidneys, leading to increased urine production.
Increased Thirst: Due to fluid loss from frequent urination, the body signals the need for more fluids.
Blurred Vision: High blood sugar can affect the lens of the eye, causing temporary blurring.
Fatigue: The body's cells aren't receiving enough glucose, leading to feelings of tiredness and weakness.
Headaches: High blood sugar can cause headaches due to changes in fluid balance.

In severe cases, hyperglycemia can lead to diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS), which are life-threatening conditions.

Dangerous High Blood Sugar Levels

A blood sugar level consistently above 250 mg/dL is generally considered dangerously high and requires prompt attention, especially if accompanied by symptoms of DKA or HHS.

Diabetic Ketoacidosis (DKA)

DKA is a severe complication primarily affecting persons with type 1 diabetes. It occurs when the body starts breaking down fat for energy because it doesn't have enough insulin to use glucose. This process produces ketones, which can build up to dangerous levels in the blood.

Symptoms of DKA:

Fruity-smelling breath
Nausea and vomiting
Abdominal pain
Rapid, deep breathing
Confusion or loss of consciousness

DKA requires immediate medical attention, often involving hospitalization for insulin therapy and fluid replacement.

Hyperosmolar Hyperglycemic State (HHS)

HHS is more common in persons with type 2 diabetes. It results from extremely high blood sugar levels, often exceeding 600 mg/dL, leading to severe dehydration and confusion.

Symptoms of HHS:

Extreme thirst
Dry mouth and skin
Warm, dry skin that does not sweat
High fever
Confusion, seizures, or coma

Like DKA, HHS is a medical emergency that requires immediate hospitalization and treatment.

Managing Hyperglycemia

Effectively managing hyperglycemia involves several strategies:

Regular Blood Sugar Monitoring: Consistent monitoring helps identify patterns and adjust treatment plans accordingly.
Insulin or Oral Medications: Follow your doctor's instructions regarding medication dosages and timing.
Dietary Adjustments: Limit intake of sugary foods and drinks, and focus on a balanced diet with controlled carbohydrate portions.
Physical Activity: Regular exercise helps improve insulin sensitivity and lowers blood sugar levels.
Hydration: Drink plenty of water to help flush out excess glucose.

Low Blood Sugar Levels (Hypoglycemia)

Hypoglycemia occurs when blood sugar levels drop too low, typically below 70 mg/dL. This can happen due to excessive insulin, skipped meals, strenuous exercise, or alcohol consumption. Hypoglycemia can be dangerous, as glucose is the primary energy source for the brain.

Symptoms of Hypoglycemia

Recognizing the symptoms of hypoglycemia is crucial for prompt treatment. Common symptoms include: The Role Of Insulin In Your Body A Guide To Blood Sugar Control

Shakiness
Sweating
Dizziness
Hunger
Irritability or anxiety
Confusion
Rapid heartbeat
Blurred vision

In severe cases, hypoglycemia can lead to seizures, loss of consciousness, and even death.

Dangerous Low Blood Sugar Levels

A blood sugar level below 55 mg/dL is considered a dangerous low and requires immediate intervention. Severe hypoglycemia, resulting in unconsciousness or seizures, is a medical emergency. Why Is Your Morning Blood Glucose So High Causes And Fixes

Managing Hypoglycemia

Treating hypoglycemia involves quickly raising blood sugar levels to a safe range. The "15-15 rule" is commonly recommended:

Check Blood Sugar: Verify that blood sugar is indeed low (below 70 mg/dL).
Consume 15 Grams of Fast-Acting Carbohydrates: Examples include:
4 ounces of juice or regular soda
1 tablespoon of honey or syrup
Glucose tablets (follow package instructions)
Wait 15 Minutes: Allow time for the blood sugar to rise.
Recheck Blood Sugar: If blood sugar is still below 70 mg/dL, repeat the process.
Eat a Meal or Snack: Once blood sugar is above 70 mg/dL, eat a meal or snack to prevent it from dropping again.

Glucagon

For individuals who are unconscious or unable to swallow, glucagon can be administered. Glucagon is a hormone that stimulates the liver to release stored glucose into the bloodstream. It is available as an injection or nasal spray and should be administered by someone trained in its use.

Preventing Hypoglycemia

Preventing hypoglycemia involves understanding and addressing its underlying causes:

Adjust Medication: Work with your doctor to adjust insulin or oral medication dosages based on your blood sugar patterns and activity levels.
Consistent Meal Timing: Eat regular meals and snacks to maintain stable blood sugar levels.
Carbohydrate Balance: Balance carbohydrate intake with medication and activity.
Alcohol Consumption: Limit alcohol intake and always consume it with food.
Exercise Planning: Monitor blood sugar before, during, and after exercise, and adjust insulin or carbohydrate intake as needed.

Factors Affecting Blood Sugar Levels

Several factors can influence blood sugar levels in persons with diabetes:

Food: The type, amount, and timing of food intake significantly impact blood sugar. Carbohydrates have the most significant effect, but protein and fat also play a role.
Physical Activity: Exercise lowers blood sugar by increasing insulin sensitivity and helping cells use glucose for energy.
Medications: Insulin and oral diabetes medications directly affect blood sugar levels.
Stress: Stress hormones can raise blood sugar by stimulating the liver to release glucose.
Illness: Illness can disrupt normal blood sugar control, often leading to higher levels.
Hormonal Changes: Hormonal fluctuations, such as those during menstruation or pregnancy, can affect blood sugar.
Dehydration: Dehydration can concentrate glucose in the blood, leading to higher blood sugar readings.

Strategies for Managing Fluctuations

To manage blood sugar fluctuations, consider the following strategies:

Keep a Food Diary: Track your food intake to identify patterns and make necessary adjustments.
Monitor Blood Sugar Regularly: Frequent monitoring provides valuable data for managing blood sugar.
Adjust Insulin Doses: Work with your healthcare provider to adjust insulin doses based on your blood sugar patterns, food intake, and activity levels.
Manage Stress: Practice stress-reduction techniques such as meditation, yoga, or deep breathing exercises.
Stay Hydrated: Drink plenty of water throughout the day.
Communicate with Your Healthcare Team: Regularly discuss your blood sugar management strategies with your healthcare team.

Long-Term Management and Complications

Consistent management of blood sugar levels is essential for preventing long-term complications of diabetes. Uncontrolled blood sugar, whether too high or too low, can lead to a range of health problems:

Common Long-Term Complications

Cardiovascular Disease: High blood sugar can damage blood vessels, increasing the risk of heart disease and stroke.
Neuropathy: Nerve damage, particularly in the feet and legs, can cause pain, numbness, and loss of sensation.
Nephropathy: Kidney damage can lead to kidney failure and the need for dialysis or a kidney transplant.
Retinopathy: Damage to the blood vessels in the retina can lead to vision loss and blindness.
Foot Problems: Nerve damage and poor circulation can increase the risk of foot ulcers, infections, and amputations.

Importance of Regular Check-Ups

Regular check-ups with your healthcare team are vital for monitoring your overall health and detecting early signs of complications. These check-ups may include:

HbA1c Tests: To assess long-term blood sugar control.
Eye Exams: To screen for retinopathy.
Kidney Function Tests: To monitor kidney health.
Foot Exams: To check for nerve damage and signs of foot problems.
Cardiovascular Assessments: To evaluate heart health.

By proactively managing your diabetes and maintaining regular check-ups, you can significantly reduce your risk of developing these complications and improve your quality of life. Surprising Factors That Affect Your Blood Sugar Levels

Conclusion

Understanding and managing blood sugar levels is crucial for persons with diabetes. Recognizing what constitutes a dangerous blood sugar level and knowing how to respond effectively can prevent acute complications like DKA, HHS, and severe hypoglycemia. Consistent monitoring, medication adherence, dietary control, regular exercise, and communication with your healthcare team are all essential components of successful diabetes management. By taking these steps, persons with diabetes can live healthier, more fulfilling lives.