What is the first next step in managing a 42-year-old male patient with a family history of diabetes, presenting with occasional fatigue and thirst, and a fasting blood sugar level of 7.2 mmol/L?

First Next Step: Repeat Fasting Blood Sugar Test

The correct answer is A: Repeat the fasting blood sugar test on a different day to confirm whether this patient has diabetes or prediabetes. A single fasting blood sugar of 7.2 mmol/L (approximately 130 mg/dL) is above the diagnostic threshold for diabetes (≥7.0 mmol/L or 126 mg/dL), but guidelines require confirmation with repeat testing before making a definitive diagnosis in the absence of unequivocal hyperglycemia 1, 2.

Why Confirmation Testing is Required

• Diagnostic criteria mandate repeat testing: In the absence of unequivocal hyperglycemia or hyperglycemic crisis, diabetes diagnosis requires two abnormal test results—either from the same sample using different tests, or from two separate samples on different days 1, 2.

• This patient lacks classic unequivocal symptoms: While he reports occasional fatigue and thirst, these are nonspecific symptoms that do not constitute the classic triad of polyuria, polydipsia, and unexplained weight loss with random glucose ≥11.1 mmol/L (200 mg/dL) that would allow immediate diagnosis without confirmation 1, 2.

• Preanalytic variability is significant: Glucose samples have substantial preanalytic and analytic variability, particularly if not centrifuged and separated immediately after collection, which can lead to falsely elevated or lowered results 1.

The Diagnostic Algorithm

Step 1: Repeat fasting plasma glucose on a different day 2, 3

• If the second FPG is also ≥7.0 mmol/L (126 mg/dL), diabetes is confirmed 1, 2
• If the second FPG is 5.6-6.9 mmol/L (100-125 mg/dL), the diagnosis is impaired fasting glucose (prediabetes) 1, 4
• If the second FPG is <5.6 mmol/L (100 mg/dL), diabetes is ruled out and the initial result was likely spurious 1

Step 2: Consider obtaining HbA1c simultaneously 2, 3

• HbA1c ≥6.5% on two occasions confirms diabetes 1, 2
• HbA1c provides information about long-term glycemic control over the preceding 2-3 months 1, 5
• If FPG and HbA1c are both above diagnostic thresholds from the same or different samples, diabetes is confirmed without need for additional testing 1

Why the Other Options Are Incorrect

Option B (Tell him to tolerate symptoms) is dangerous and inappropriate:

• Delaying diagnosis allows progression of hyperglycemia and increases risk of end-organ damage to eyes, kidneys, nerves, heart, and blood vessels 6, 5
• Even if this turns out to be prediabetes rather than diabetes, early intervention with lifestyle modification reduces progression to diabetes by up to 58% 4
• Fatigue in diabetes is associated with poor self-management and quality of life, and should not be dismissed 7

Option C (Start metformin immediately) is premature:

• The diagnosis has not been confirmed yet—a single elevated FPG requires verification 1, 2
• If confirmed diabetic with FPG 7.2 mmol/L and only mild symptoms, this patient would be metabolically stable and metformin would be appropriate first-line therapy 2
• However, metformin should only be initiated after confirming the diagnosis and checking renal function 8
• Starting treatment before confirming diagnosis could lead to unnecessary medication exposure and potential adverse effects including lactic acidosis risk 8

Important Clinical Pitfalls to Avoid

• Don't diagnose diabetes from a single test unless there is hyperglycemic crisis: The requirement for confirmation testing exists precisely because of test variability and the lifelong implications of a diabetes diagnosis 1.

• Don't delay confirmation testing: While repeat testing is required, it should be performed "without delay" on a different day, not weeks or months later 1, 2.

• Consider checking for ketones if glucose is markedly elevated: Although this patient's glucose is only mildly elevated, if repeat testing shows marked hyperglycemia (≥13.9 mmol/L or 250 mg/dL), check for ketones to rule out diabetic ketoacidosis, which would require immediate insulin therapy 2, 9.

• Screen for other cardiovascular risk factors: Given his family history and potential diabetes diagnosis, assess fasting lipid profile, blood pressure, and consider screening for other metabolic syndrome components 10.