Normal Random Blood Sugar (RBS) Levels
For adults without diabetes, a normal random blood sugar level is below 140 mg/dL (7.8 mmol/L), while values ≥200 mg/dL (11.1 mmol/L) with classic symptoms indicate diabetes. 1
For Adults WITHOUT Diabetes
Normal Range
- Random blood glucose should be <140 mg/dL (7.8 mmol/L) in healthy adults 1
- In a large cohort of physically active adults without diabetes, 85% maintained 24-hour average glucose between 90-110 mg/dL, with men averaging 100 ± 11 mg/dL and women 96 ± 10 mg/dL 2
- Fasting glucose in healthy adults ranges from 70-100 mg/dL (3.9-5.6 mmol/L) 3
Concerning Values Requiring Further Testing
- Random glucose 140-180 mg/dL (7.8-10.0 mmol/L) has 92-98% specificity for diabetes and warrants definitive testing with fasting glucose or HbA1c 1
- Random glucose ≥100 mg/dL (5.6 mmol/L) is strongly associated with undiagnosed prediabetes or diabetes (odds ratio 31.2) and should prompt formal screening 4
Diagnostic Thresholds
- Random glucose ≥200 mg/dL (11.1 mmol/L) with classic symptoms (polyuria, polydipsia, weight loss, blurred vision, fatigue) confirms diabetes without need for repeat testing 1, 5
- Impaired fasting glucose (prediabetes): 100-125 mg/dL (5.6-6.9 mmol/L) 6, 7
- Diabetes diagnosis (fasting): ≥126 mg/dL (≥7.0 mmol/L) on two separate occasions 6
For Adults WITH Diabetes
Target Ranges (American Diabetes Association Guidelines)
- Preprandial (before meals): 80-130 mg/dL (4.4-7.2 mmol/L) 1
- Postprandial (1-2 hours after meals): <180 mg/dL (<10.0 mmol/L) 1
- Time in range goal: >70% of readings between 70-180 mg/dL (3.9-10.0 mmol/L) 1
Hypoglycemia Thresholds
- Level 1 hypoglycemia: <70 mg/dL (3.9 mmol/L) - requires treatment with 15-20g fast-acting carbohydrates 1, 6
- Level 2 hypoglycemia: <54 mg/dL (3.0 mmol/L) - neuroglycopenic symptoms begin, requires immediate action 1
- Severe hypoglycemia: <40 mg/dL (2.2 mmol/L) - medical emergency 6
Hyperglycemia Thresholds
- Time above range Level 1: 181-250 mg/dL (10.1-13.9 mmol/L) - should be <25% of time 1
- Time above range Level 2: >250 mg/dL (>13.9 mmol/L) - should be <5% of time 1, 6
- Severe hyperglycemia: >300 mg/dL (>16.7 mmol/L) 6
Critical Clinical Pitfalls
- Do not dismiss random glucose values of 140-180 mg/dL - these have high specificity (92-98%) for diabetes and require confirmatory testing rather than reassurance 1
- Always document whether the patient has eaten recently - postprandial values up to 180 mg/dL may be acceptable in diabetics, but the same value while fasting is concerning 1
- When reviewing international literature, verify units (mg/dL vs mmol/L) - North America uses mg/dL while most other countries use mmol/L; divide mg/dL by 18 to convert to mmol/L 6
- In emergency department settings, 42% of patients with elevated random glucose (mean 181 mg/dL) are discharged without being informed or referred - this represents a critical missed opportunity for diabetes prevention 8