MKSAP Quiz: Lower hemoglobin A1c after surgery
This month's quiz asks readers to evaluate a 56-year-old man with type 2 diabetes in a follow-up after repair of a bleeding duodenal ulcer.
A 56-year-old man comes to the office for a follow-up evaluation. Three weeks ago, the patient had surgery to repair a bleeding duodenal ulcer. During his 7-day hospitalization, he was given six units of packed red blood cells. He was discharged 2 weeks ago with instructions to take omeprazole. The patient has a 12-year history of type 2 diabetes mellitus, and his hemoglobin A1c values have ranged from 8.5% to 9.0% for the past 5 years. Since hospital discharge, his blood glucose levels have ranged from 140 to 160 mg/dL (7.8-8.9 mmol/L). He has a 40-pack-year smoking history but has not smoked since the surgery. Although work was increasingly stressful before ulcer repair, he says he has been feeling more relaxed since discharge and has been eating healthier foods. Medications are metformin, glyburide, simvastatin, and omeprazole.
On physical examination, temperature is 36.9 °C (98.4 °F), blood pressure is 142/83 mm Hg, pulse rate is 82/min, and respiration rate is 14/min; BMI is 34. Other physical examination findings are unremarkable.
Results of laboratory studies show a hematocrit of 43% and a hemoglobin A1c value of 6.2% (estimated average plasma glucose level, 130 mg/dL [7.2 mmol/L]).
Which of the following best explains the reduction in his hemoglobin A1c value?
A. Blood transfusions
B. Healthier diet
C. Omeprazole interference with the hemoglobin A1c assay
D. Smoking cessation
MKSAP Answer and Critique
The correct answer is A. Blood transfusions. This item is available to MKSAP 16 subscribers as item 37 in the Endocrinology section. Information about MKSAP 16 is available online.
The six units of packed red blood cells that this patient received while hospitalized most likely are responsible for his low hemoglobin A1c value. In patients receiving hemodialysis, those with hemolytic anemia or certain hemoglobinopathies, or those with recent blood transfusions, hemoglobin A1c values may be falsely lowered because of the presence of erythrocytes less than 120 days old in the sample. In this patient, not enough time has elapsed since the blood was transfused for the erythrocytes to become glycosylated and reflect a true hemoglobin A1c level.
Although eating a healthier diet might lower his blood glucose levels over the next few months, not enough time has passed for this lifestyle intervention to affect his hemoglobin A1c value so profoundly. His blood glucose log shows premeal values of 140 to 160 mg/dL (7.8-8.9 mmol/L), which means that postprandial values are likely to be even higher and not compatible with a hemoglobin A1c value of 6.2%.
Omeprazole does not interfere with hemoglobin A1c assays and thus is not responsible for his dramatically lower value.
Cessation of cigarette smoking, although an inherently positive lifestyle change, will not affect the hemoglobin A1c level.
Key Point
- Hemoglobin A1c values may be falsely lowered in patients who have received recent blood transfusions.