Is This Diabetes?
No, a fasting blood sugar of 104 mg/dL with an HbA1c of 5.3% does not meet diagnostic criteria for diabetes—this represents normal glucose metabolism with a slightly elevated fasting glucose that falls into the impaired fasting glucose (IFG) range. 1
Understanding the Diagnostic Criteria
To diagnose diabetes, you need one of the following confirmed on two separate occasions 1:
- Fasting plasma glucose ≥126 mg/dL (not met—patient has 104 mg/dL)
- HbA1c ≥6.5% (not met—patient has 5.3%)
- 2-hour glucose ≥200 mg/dL during oral glucose tolerance test (not tested)
- Random glucose ≥200 mg/dL with classic hyperglycemic symptoms (not applicable)
What These Numbers Actually Mean
The HbA1c of 5.3% is completely normal and reflects an estimated average glucose of approximately 105 mg/dL over the past 2-3 months. 2, 3 This value is well below the 5.7% threshold that defines prediabetes. 1, 2
The fasting glucose of 104 mg/dL falls into the impaired fasting glucose (IFG) category, defined as 100-125 mg/dL. 1 However, this single elevated value does not establish a diagnosis, particularly when the HbA1c—which reflects long-term glucose control—is entirely normal.
Why the Discordance?
When test results are discordant (one abnormal, one normal), the test above the diagnostic threshold should be repeated. 1 In this case:
- The fasting glucose is mildly elevated but below the diabetes threshold of 126 mg/dL
- The HbA1c is normal at 5.3%, indicating good average glucose control over 2-3 months
Linear regression data from NHANES shows that an HbA1c of 5.4% corresponds to a fasting glucose of approximately 100 mg/dL, so a fasting glucose of 104 mg/dL with an HbA1c of 5.3% is actually quite concordant and expected. 1, 2
Addressing the "Night Before" Question
Yes, what someone ate the night before can affect fasting glucose levels. 1 Common causes of mildly elevated fasting glucose without diabetes include:
- Inadequate fasting duration (should be at least 8 hours)
- Recent illness or stress
- Certain medications
- Laboratory variability (glucose samples must be spun and separated immediately to avoid falsely elevated results) 1
The HbA1c is not affected by recent food intake, which is why it's particularly valuable here—it confirms that average glucose control over the past 2-3 months has been normal. 1, 2
Clinical Recommendation
This patient does not have diabetes or even prediabetes. 1, 2 The appropriate next steps are:
- Repeat fasting glucose testing in 3-6 months to confirm whether the mildly elevated value persists 1
- Continue routine screening at 3-year intervals if repeat testing is normal 2
- Screen more frequently if BMI is increasing or other risk factors develop 2
Individuals with HbA1c below 5.7% may still have some diabetes risk depending on obesity and family history, but this patient's current glucose metabolism is normal. 1, 2