Glucose is the main sugar in the blood and the body's primary source of energy. Blood glucose levels are tightly regulated by insulin and are central to the diagnosis and management of diabetes.
Glucose is a simple sugar (monosaccharide) that serves as the primary fuel for cells throughout the body, including the brain. It is obtained from carbohydrates in food — when you eat bread, rice, fruit, or sweets, your digestive system breaks them down into glucose, which then enters the bloodstream.
The hormone insulin, produced by the pancreas, acts like a key to allow cells to absorb glucose from the blood for energy. When this system works correctly, blood glucose levels remain in a healthy range. In type 1 diabetes, the pancreas cannot produce insulin. In type 2 diabetes — by far the most common form, and rising steadily in Korea as the population ages — cells become resistant to insulin's effects, causing blood glucose to rise. Chronically elevated blood glucose (hyperglycaemia) damages blood vessels and nerves, leading to complications affecting the heart, kidneys, eyes, and feet.
Blood glucose is measured in Korea using several tests: fasting blood glucose (after 8 hours without food), random blood glucose, HbA1c (average blood glucose over 3 months), and the oral glucose tolerance test (OGTT). Normal fasting glucose is 3.9–5.6 mmol/L. Prediabetes is 5.6–6.9 mmol/L. Diabetes is diagnosed at 7.0 mmol/L or above on two separate occasions.
Key Points
- Glucose is the body's primary energy source — derived from dietary carbohydrates
- Normal fasting blood glucose: 3.9–5.6 mmol/L
- Prediabetes: fasting glucose 5.6–6.9 mmol/L
- Diabetes diagnosed when fasting glucose ≥7.0 mmol/L on two occasions
- HbA1c test measures average blood glucose over the past 3 months
- Korea has a rising rate of type 2 diabetes, driven by an aging population and dietary change — glucose monitoring is important
When to See a Doctor
- Fasting blood glucose above 5.6 mmol/L on a routine test
- Symptoms of high blood sugar: excessive thirst, frequent urination, fatigue, blurred vision
- Symptoms of low blood sugar: shakiness, sweating, confusion, palpitations
- Annual glucose testing recommended for adults over 40, overweight, or with family history of diabetes
For emergencies in Korea, call 119
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This article is published by DoctorsInKorea.com for educational and informational purposes only. It does not replace a professional clinical evaluation by a licensed healthcare provider. For accurate medical diagnosis and personalised treatment paths, please book an appointment with a licensed KMA physician. For immediate life-threatening medical emergencies in Korea, please call 119.
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Last reviewed: March 1, 2025