What is the next step for a patient with a family history of diabetes, presenting with occasional fatigue and thirst, and a fasting blood sugar level of 7.2?

Repeat the Fasting Blood Sugar Test

The correct next step is to repeat the fasting blood sugar test on a different day to confirm the diagnosis (Option A). A single FBS of 7.2 mmol/L (129.6 mg/dL) exceeds the diagnostic threshold for diabetes (≥7.0 mmol/L or ≥126 mg/dL), but confirmation with repeat testing is required before establishing the diagnosis and initiating treatment 1.

Diagnostic Rationale

• The patient's FBS of 7.2 mmol/L meets the glucose criterion for diabetes (≥7.0 mmol/L), but this represents only a single measurement 1
• Standard diagnostic protocols mandate confirmation by repeat testing unless the patient presents with unequivocal hyperglycemia (random glucose ≥11.1 mmol/L with classic symptoms) or hyperglycemic crisis 1
• This patient has only "occasional" fatigue and thirst, which do not constitute the severe classic hyperglycemic symptoms (marked polyuria, polydipsia, unexplained weight loss) that would allow diagnosis on a single test 1

How to Confirm the Diagnosis

Repeat the same test (fasting plasma glucose) on a subsequent day, as this provides the greatest likelihood of concordance and minimizes diagnostic uncertainty 1:

• If the repeat FBS is ≥7.0 mmol/L (≥126 mg/dL), the diagnosis of diabetes is confirmed 1
• If the repeat FBS is 5.6-6.9 mmol/L (100-125 mg/dL), the patient has impaired fasting glucose (prediabetes) 1, 2
• If the repeat FBS is <5.6 mmol/L (<100 mg/dL) but the first test was truly elevated, consider alternative testing such as HbA1c or oral glucose tolerance test 1

Alternatively, you can use a different test for confirmation (HbA1c ≥6.5% or 2-hour OGTT ≥11.1 mmol/L), and if both the initial FBS and the alternative test are above diagnostic thresholds, diabetes is confirmed without needing to repeat the FBS 1

Why Other Options Are Incorrect

• Option B (tell him to tolerate symptoms) is dangerous and inappropriate: This patient has a family history of diabetes, symptoms suggestive of hyperglycemia, and an elevated FBS that requires diagnostic confirmation 1, 3
• Option C (start metformin immediately) is premature: Treatment should not begin until the diagnosis is confirmed with repeat testing, as preanalytic and analytic variability can cause false elevations 1

Common Pitfalls to Avoid

Do not start treatment based on a single glucose measurement unless the patient has unequivocal hyperglycemia with classic symptoms or hyperglycemic crisis 1:

• Laboratory errors and preanalytic variability occur, making confirmation essential 1
• When a test result near the diagnostic threshold is repeated, the second value may fall below the cutpoint, particularly with FPG 1

Do not dismiss mild symptoms in high-risk patients: This 42-year-old with a first-degree relative with diabetes has multiple risk factors (family history, symptomatic) warranting thorough diagnostic evaluation 1, 2, 3

Ensure proper testing conditions: Fasting is defined as no caloric intake for at least 8 hours, and the test should be performed on venous plasma in a certified laboratory 1