In a 55-year-old man with a family history of type 2 diabetes, blood pressure 130/85 mmHg, heart rate 80/min, height 185 cm, weight 91 kg, fasting glucose 7.4 mmol/L (reference 3.5‑6.5) and hemoglobin A1c 6.3% (reference 4.7‑5.6%), which test should be recommended next?

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Last updated: October 3, 2026 • View editorial policy

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Repeat the Fasting Plasma Glucose Test

This patient should have a repeat fasting plasma glucose (FPG) test performed without delay to confirm the diagnosis of diabetes (Option C is correct). 1, 2, 3

Diagnostic Criteria and Confirmation Requirements

This patient has two abnormal screening results from a single testing occasion:

  • Fasting glucose: 7.4 mmol/L (diagnostic threshold: ≥7.0 mmol/L)
  • HbA1c: 6.3% (diagnostic threshold: ≥6.5%)

Why Repeat FPG is the Correct Choice

According to ADA guidelines, when test results are discordant (one above and one below the diagnostic threshold), the test that exceeds the diagnostic cut point should be repeated to confirm the diagnosis 1, 2, 3. In this case:

  • The FPG of 7.4 mmol/L is above the diagnostic threshold (≥7.0 mmol/L = ≥126 mg/dL)
  • The HbA1c of 6.3% is below the diagnostic threshold (<6.5%)

The diagnosis is made based on the confirmed abnormal test. If the repeat FPG is ≥7.0 mmol/L (≥126 mg/dL), diabetes is confirmed even though the HbA1c remains below 6.5% 1, 4, 1.

Why Other Options Are Incorrect

Option A (Random plasma glucose): Not appropriate for diagnostic confirmation. Random glucose is only diagnostic when ≥200 mg/dL (11.1 mmol/L) in the presence of classic hyperglycemic symptoms 1, 2.

Option B (HbA1c after 6 weeks): Incorrect timing and wrong test. The HbA1c is currently below the diagnostic threshold (6.3% vs. required ≥6.5%), so repeating it would not confirm diabetes. Additionally, guidelines recommend repeating the test "without delay" or within 3-6 months if results are marginal 2, 3.

Option D (OGTT): Not indicated when FPG already exceeds the diagnostic threshold. The OGTT is reserved for situations when FPG is <7.0 mmol/L but diabetes is still suspected 5, 2.

Clinical Context

This patient has multiple risk factors warranting diabetes screening:

  • Age 55 years
  • Family history of type 2 diabetes
  • BMI 26.6 kg/m² (overweight: 91 kg ÷ 1.85² m)
  • Blood pressure 130/85 mmHg (elevated)

Important Caveats

Preanalytical considerations: When repeating FPG, ensure proper sample handling. Blood should be:

  • Drawn after an 8-hour overnight fast 1, 6
  • Collected in tubes with rapidly effective glycolytic inhibitors (granulated citrate buffer)
  • Placed immediately in ice-water slurry and centrifuged within 15-30 minutes if glycolytic inhibitors are not used 6

If the repeat FPG is <7.0 mmol/L: The patient would be classified as having prediabetes (impaired fasting glucose) given the initial FPG of 7.4 mmol/L and HbA1c of 6.3%. Close follow-up with repeat testing in 3-6 months would then be appropriate 1.

References

5
Guideline

screening for type 2 diabetes.

Diabetes Care, 2003

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