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Screening and confirmation of type 2 diabetes when hemoglobin A1c is unreliable after transfusion — ABIM Board

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HardDiabetes ScreeningScreening and confirmation of type 2 diabetes when hemoglobin A1c is unreliable after transfusionABIM Board

A 52-year-old man is seen for preventive care. He has hypertension and obesity (BMI, 32 kg/m²) but no polyuria, polydipsia, weight loss, or prior diagnosis of diabetes mellitus. Six weeks ago, he sustained multiple traumatic injuries with substantial blood loss and received 4 units of packed red blood cells. He has recovered and is taking no glucocorticoids. Laboratory testing after an overnight fast shows a plasma glucose level of 132 mg/dL and a laboratory-measured hemoglobin A1c of 5.4%. Hemoglobin is now 12.8 g/dL. Which of the following is the most appropriate testing strategy?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: E — Obtain a repeat fasting plasma glucose promptly

Explanation lettering: B = shown as A · E = shown as B · A = shown as E

This patient meets USPSTF criteria for screening because he is age 35–70 years and has obesity. His fasting plasma glucose of 132 mg/dL exceeds the diagnostic threshold for diabetes (126 mg/dL), but he has no classic hyperglycemic symptoms or crisis; therefore, a second abnormal result is required before establishing the diagnosis. The repeat test should be performed promptly. Recent major blood loss and packed red-cell transfusion alter erythrocyte age and turnover, making the A1c–glycemia relationship unreliable. Plasma glucose criteria should therefore be used, making repeat fasting plasma glucose the best strategy. Repeating A1c promptly (B) would reproduce a test that is currently unreliable. Fructosamine (C) can help assess short-term glycemia when A1c is unreliable in a patient with established diabetes, but it is not a standard diagnostic criterion. Waiting 3 months to repeat A1c (D) might reduce transfusion-related distortion but unnecessarily delays confirmation of an already abnormal fasting glucose. A 3-year interval (E) is reasonable after normal screening, not after a diabetes-range result.

Reference: 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026 (January 1, 2026) — https://pmc.ncbi.nlm.nih.gov/articles/PMC12690183/ Final Recommendation Statement: Prediabetes and Type 2 Diabetes: Screening (August 24, 2021) — https://www.uspreventiveservicestaskforce.org/uspstf/document/RecommendationStatementFinal/screening-for-prediabetes-and-type-2-diabetes