What Could Cause Blood Glucose to be 108 mg/dL?
A blood glucose of 108 mg/dL is completely normal and does not indicate diabetes or prediabetes—this value falls within the normal fasting range and requires no intervention. 1, 2
Understanding Your Result
Your blood glucose of 108 mg/dL falls into the normal range regardless of whether this was a fasting or random measurement:
If this was a fasting glucose: Normal fasting glucose is defined as <100 mg/dL, with impaired fasting glucose (prediabetes) starting at 100-125 mg/dL. 3, 1 However, the older diagnostic threshold of <110 mg/dL was previously used, and your value of 108 mg/dL would have been considered normal under those criteria. 3
If this was a random (non-fasting) glucose: Random blood glucose values below 140 mg/dL are considered normal and do not require further diagnostic testing for diabetes. 2 Your value of 108 mg/dL is well below this threshold.
What Causes Normal Blood Glucose Fluctuations
Normal blood glucose levels like 108 mg/dL result from:
- Recent food intake: If measured non-fasting, this reflects normal glucose metabolism after eating 3
- Normal physiologic variation: Fasting glucose has a 12-15% day-to-day variance even in healthy individuals 3
- Time of day effects: Glucose levels naturally fluctuate throughout the day 3
- Physical activity level: Exercise affects glucose utilization 3
When to Consider Further Testing
You would only need additional diabetes screening if you have specific risk factors, despite your normal glucose reading: 3
- Sustained blood pressure >135/80 mm Hg 3
- Hypertension or hyperlipidemia 3
- BMI ≥25 kg/m² 4
- Family history of diabetes in first-degree relatives 4
- Sedentary lifestyle 4
- History of gestational diabetes 4
- Membership in high-risk ethnic groups (Hispanic American, Native American, Asian American, African-American, Pacific Islander) 3, 4
Clinical Context
Your value of 108 mg/dL does not suggest impaired glucose metabolism and falls within normal parameters. 2 For comparison, concerning values would be:
- Impaired fasting glucose (prediabetes): 100-125 mg/dL 3, 1
- Diabetes diagnosis (fasting): ≥126 mg/dL on two separate occasions 3, 1
- Diabetes diagnosis (random with symptoms): ≥200 mg/dL 3
Important Caveats
The diagnostic threshold for impaired fasting glucose was lowered from 110 mg/dL to 100 mg/dL in 2003, which means your value of 108 mg/dL sits in a gray zone between the old and new criteria. 3 However, even under the newer, more stringent criteria, values in the 100-109 mg/dL range carry relatively low risk—only 8.1% of people with initial fasting glucose of 100-109 mg/dL progress to diabetes, at a rate of 1.34% per year. 5 This contrasts sharply with fasting glucose of 110-125 mg/dL, where 24.3% develop diabetes at a rate of 5.56% per year. 5
No action is needed for a blood glucose of 108 mg/dL unless you have multiple diabetes risk factors warranting routine screening. 3, 2