Normal Random Blood Sugar (RBS) Levels
A normal random blood sugar level is less than 140 mg/dL (7.8 mmol/L), with values below 100 mg/dL (5.6 mmol/L) considered optimal in individuals without diabetes. 1
Defining Normal RBS Values
Standard Thresholds
- Below 100 mg/dL (5.6 mmol/L): Optimal normal range in non-diabetic individuals 2
- 100-140 mg/dL (5.6-7.8 mmol/L): Borderline elevated; warrants further evaluation 1, 2
- Above 140 mg/dL (7.8 mmol/L): Threshold for considering inpatient hyperglycemia or need for diagnostic testing 1
Clinical Context Matters
The interpretation of RBS depends heavily on the clinical setting:
Outpatient/Community Setting: Values consistently ≥100 mg/dL should prompt formal diabetes screening with fasting glucose or HbA1c, as a single RBS ≥100 mg/dL is strongly associated with undiagnosed diabetes (odds ratio 31.2) 2
Hospitalized Non-Critically Ill Patients: Target random glucose <180 mg/dL (10.0 mmol/L), with premeal targets <140 mg/dL (7.8 mmol/L) 1
Critically Ill ICU Patients: Target range 140-180 mg/dL (7.8-10.0 mmol/L) once insulin therapy is initiated 1
Risk Stratification by RBS Level
The risk of undiagnosed diabetes increases dramatically with rising RBS values, even below the traditional diagnostic threshold of 200 mg/dL: 2
- RBS 100-119 mg/dL: 7-fold increased odds of undiagnosed diabetes
- RBS 120-139 mg/dL: 30-fold increased odds of undiagnosed diabetes
- RBS ≥140 mg/dL: 256-fold increased odds of undiagnosed diabetes
This gradient demonstrates that RBS values well below the diagnostic threshold (≥200 mg/dL) provide critical information about diabetes risk and should not be dismissed as "normal" without further evaluation. 2
Hypoglycemia Thresholds
Understanding the lower boundary of normal is equally important:
- 70-180 mg/dL (3.9-10.0 mmol/L): Target range for individuals with diabetes using continuous glucose monitoring 1
- <70 mg/dL (3.9 mmol/L): Level 1 hypoglycemia; clinically important threshold requiring attention 1
- <54 mg/dL (3.0 mmol/L): Level 2 hypoglycemia; threshold for neuroglycopenic symptoms requiring immediate action 1
Common Pitfalls to Avoid
Do not assume RBS values between 100-140 mg/dL are "normal" without further investigation. Research demonstrates these values carry substantial diabetes risk and should trigger formal screening. 2, 3
Do not use RBS interchangeably with fasting glucose or HbA1c-derived estimated average glucose (eAG). While RBS correlates with these measures in diabetic populations, they cannot be used interchangeably and serve different clinical purposes. 4
Do not ignore a single elevated RBS value. A single RBS ≥100 mg/dL is more strongly associated with undiagnosed diabetes than traditional risk factors including age, BMI, family history, or hypertension. 2
Recognize that "random" means non-fasting, but timing relative to meals still matters. Values obtained 1-2 hours postprandially will be higher than true random values obtained at other times. 1