What is the next step for a patient with a fasting plasma glucose level of 145 mg/dl, indicating hyperglycemia, and well-controlled hypertension, who is otherwise asymptomatic with normal vital signs and laboratory results?

Next Step: Repeat Fasting Plasma Glucose

You should repeat the fasting plasma glucose test to confirm the diagnosis of diabetes before initiating any treatment or further diagnostic workup. 1

Rationale for Confirmatory Testing

The patient's single fasting plasma glucose of 145 mg/dL exceeds the diagnostic threshold for diabetes (≥126 mg/dL), but current guidelines require confirmation before establishing a definitive diagnosis. 1

• In the absence of unequivocal hyperglycemia (such as hyperglycemic crisis with random glucose ≥200 mg/dL plus classic symptoms), diagnosis requires two abnormal test results—either from the same sample using different tests, or the same test repeated on a separate occasion. 1

• This patient lacks classic symptoms of hyperglycemia (polyuria, polydipsia, unexplained weight loss) and has normal vital signs, making this a case requiring confirmatory testing rather than immediate diagnosis. 1

• The American Diabetes Association explicitly states that when a single test exceeds the diagnostic threshold without symptoms or crisis, the abnormal result should be repeated without delay. 1

Why Not the Other Options

Option B (Low-carbohydrate diet): While lifestyle modification will ultimately be important, you cannot recommend diabetes-specific dietary interventions before confirming the diagnosis. Premature labeling as diabetic has significant medical, psychological, and insurance implications. 1

Option C (Urine microalbumin): Screening for diabetic nephropathy is premature when diabetes itself has not been confirmed. Microalbuminuria screening is appropriate for established diabetes patients, not for diagnostic confirmation. 1

Option D (Start metformin): Initiating pharmacotherapy before diagnostic confirmation violates standard practice guidelines. The FDA label for metformin indicates use in patients with type 2 diabetes mellitus—a diagnosis that has not yet been established in this patient. 2

Practical Considerations for Repeat Testing

When performing the confirmatory fasting plasma glucose:

• Ensure proper fasting of at least 8 hours with no caloric intake. 1
• Test in the morning after an overnight fast for optimal standardization. 3
• Process samples promptly—glucose samples should be centrifuged and separated immediately to avoid preanalytic variability that can falsely lower results if left at room temperature. 1
• Perform testing without delay rather than waiting weeks or months, as recommended by current guidelines. 1

Interpretation of Confirmatory Results

If repeat FPG ≥126 mg/dL: Diabetes is confirmed, and you should then proceed with comprehensive diabetes management including lifestyle modifications, consideration of metformin (given normal renal function with eGFR >60), and screening for complications including microalbuminuria. 1, 2

If repeat FPG 100-125 mg/dL: The patient has impaired fasting glucose (prediabetes), warranting intensive lifestyle intervention and consideration of repeat testing in 3-6 months. 1

If repeat FPG <100 mg/dL: The initial result may have reflected preanalytic variability, recent stress, or transient hyperglycemia. Consider alternative testing with HbA1c or oral glucose tolerance test if clinical suspicion remains high. 1

Important Caveats

• Preanalytic variability is particularly problematic with glucose measurements—samples left at room temperature without prompt centrifugation can show falsely low values due to ongoing glycolysis. 1

• The patient's hypertension increases cardiovascular risk regardless of glucose status, so while awaiting confirmatory testing, continue optimizing blood pressure control and cardiovascular risk reduction. 1

• If the repeat test shows discordant results near diagnostic margins, discuss symptoms with the patient and consider repeating testing in 3-6 months. 1