What is a normal glucose level for an adult with or without diabetes?

Normal Glucose Levels

For adults without diabetes, normal fasting glucose is 70-100 mg/dL, with postprandial values remaining below 140 mg/dL at 1-2 hours after meals. 1, 2

For Individuals Without Diabetes

Fasting Glucose

• Normal fasting capillary blood glucose: 70-100 mg/dL (3.9-5.6 mmol/L) 1, 2
• Values below 70 mg/dL indicate hypoglycemia requiring treatment 1, 2

Postprandial Glucose

• Normal postprandial glucose: <140 mg/dL (7.8 mmol/L) at 1-2 hours after meals 1
• Random glucose in healthy individuals should remain <140 mg/dL 2

Prediabetes Thresholds

• Impaired fasting glucose (prediabetes): 100-125 mg/dL 1, 3
• Impaired glucose tolerance: 140-199 mg/dL at 2 hours on 75-g oral glucose tolerance test 1, 3
• Individuals with prediabetes progress to diabetes at approximately 10% per year 3

Diabetes Diagnostic Thresholds

• Fasting glucose ≥126 mg/dL on two separate occasions confirms diabetes 1
• Random glucose ≥200 mg/dL with classic symptoms (polyuria, polydipsia, weight loss) confirms diabetes without repeat testing 1

For Individuals With Diabetes

Target Glucose Ranges

• Preprandial (before meals): 80-130 mg/dL (4.4-7.2 mmol/L) 1, 2
• Peak postprandial (after meals): <180 mg/dL (10.0 mmol/L) 1, 2
• A1C target: <7.0% (53 mmol/mol) 1, 2

Hypoglycemia Definitions and Actions

• Level 1 hypoglycemia: <70 mg/dL but ≥54 mg/dL - requires attention and treatment with 15-20g fast-acting carbohydrates 1, 4, 2
• Level 2 hypoglycemia: <54 mg/dL (3.0 mmol/L) - neuroglycopenic symptoms begin, requiring immediate action 1, 4, 2
• After treating hypoglycemia, recheck glucose in 15 minutes and repeat treatment if still low 1, 4, 2

Hyperglycemia Alert Thresholds

For patients in long-term care or requiring monitoring, contact providers when: 5

• Glucose values are >250 mg/dL within a 24-hour period 5
• Glucose values are >300 mg/dL over 2 consecutive days 5

Important Clinical Caveats

Diagnostic Limitations

• Random capillary blood glucose alone has limited diagnostic value with only 75-80% sensitivity and specificity for detecting diabetes 1
• Always confirm diabetes diagnosis with repeat testing on a separate day unless random glucose ≥200 mg/dL with classic symptoms 1

Special Populations

For older adults at end of life, glucose targets are liberalized to prevent hypoglycemia, with acceptable values in the upper range of targets and focus on keeping levels below the renal threshold 5