Medical Emergencies · patient case question
The physician orders an HbA1c. What does this test measure?
Patient case: A Diabetic Who Does Not Check His Sugar
Patient: 56-year-old male
Chief Complaint: Broken tooth, wants it fixed.
Background: Type 2 diabetes for nine years. When asked about his blood glucose he says he does not test it and has not seen his physician in over a year. Reports increasing thirst and getting up at night to urinate.
Medications: Metformin — admits he is inconsistent with it
Vital Signs: BP 138/86 mmHg · HR 82 bpm · RR 16 · T 98.6°F
Findings: Generalized gingival inflammation with bleeding on probing, multiple 5–6 mm pockets, dry mucosa, and a fractured cusp on #14.
Show answer and explanation
Correct answer: B. The proportion of haemoglobin that has become glycated, reflecting average glucose over 2–3 months
- A. Urinary glucose (glycosuria) appears once the renal threshold of about 180 mg/dL is exceeded. It is a crude and outdated screen.
- B. CORRECT. HbA1c is GLYCATED HAEMOGLOBIN — glucose binds non-enzymatically and irreversibly to haemoglobin in proportion to how much glucose the red cell has been exposed to. Because red cells live about 120 days, the result reflects average glycaemia over roughly the preceding 8–12 weeks and cannot be manipulated by fasting on the morning of the test. Targets: under 5.7% normal, 5.7–6.4% prediabetes, 6.5% or above diabetic, and under 7% is the usual treatment goal.
- C. Beta-cell reserve is assessed with C-peptide, which is co-secreted with endogenous insulin and distinguishes endogenous from injected insulin.
- D. That is a capillary or venous glucose measurement — a single point in time, which is precisely the limitation HbA1c overcomes.
Note: HbA1c is unreliable where red cell lifespan is abnormal — haemolytic anaemia, recent transfusion, chronic kidney disease, pregnancy and some haemoglobinopathies all distort it.
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