Repeat the Fasting Blood Sugar Test
The first next step is to repeat the fasting blood sugar test on a separate day to confirm the diagnosis of diabetes before initiating any treatment. 1, 2
Why Confirmation Testing is Required
Your patient's FBS of 7.2 mmol/L (130 mg/dL) meets the diagnostic threshold for diabetes (≥7.0 mmol/L or ≥126 mg/dL), but this represents only a single measurement. 1, 2 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, 2
The American Diabetes Association explicitly states that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds. 1 While your patient has symptoms (fatigue and polydipsia), these are not accompanied by a random glucose ≥200 mg/dL (11.1 mmol/L), so confirmation testing is still required. 1
How to Confirm the Diagnosis
Repeat the same test (FBS) on a subsequent day for the greatest likelihood of concordance and to minimize diagnostic uncertainty. 1, 2 If the repeat FBS is ≥7.0 mmol/L (≥126 mg/dL), the diagnosis of diabetes is confirmed. 2, 3
Alternatively, use a different test for confirmation (HbA1c ≥6.5% or 2-hour OGTT ≥11.1 mmol/L). If both the initial FBS and the alternative test are above diagnostic thresholds, diabetes is confirmed without needing to repeat the FBS. 1, 2
Ensure proper testing conditions: The patient must fast for at least 8 hours, and the test should be performed on venous plasma in a certified laboratory. 2, 3
Why Not Start Metformin Immediately
Do not start treatment based on a single glucose measurement unless the patient has unequivocal hyperglycemia with classic symptoms or hyperglycemic crisis. 2 Laboratory errors and preanalytic variability occur (12-15% day-to-day variance in fasting blood glucose values), making confirmation essential before committing a patient to lifelong diabetes treatment. 1, 2
Why Not Dismiss the Symptoms
Telling the patient to tolerate symptoms and return if they worsen is inappropriate. 4 The patient has a positive family history, symptoms consistent with hyperglycemia, and a borderline-to-diagnostic FBS result. 4 This warrants prompt diagnostic confirmation, not watchful waiting. 1, 2
Common Pitfalls to Avoid
Starting treatment prematurely: A single elevated glucose value near the diagnostic threshold may not represent true diabetes due to laboratory variability. 1, 2
Using capillary glucometry alone: While glucometry can be useful for screening, abnormal results must be confirmed with standardized laboratory tests using venous plasma samples. 3
Ignoring the need for proper fasting: Ensure the patient understands the 8-hour fasting requirement for accurate results. 3