Medical Emergencies · patient case question
HbA1c provides each of the following EXCEPT one. Which is the EXCEPTION?
Patient case: HIV with poorly controlled diabetes
Patient: Male, 47 years old
Chief complaint: “My gums bleed and my mouth is always dry.”
History: HIV, on antiretroviral therapy, CD4 460 cells/mm³, viral load undetectable. Type 2 diabetes mellitus. Asthma, well controlled with an as-needed inhaler.
Findings: Laboratory results today: HbA1c 10%, CD4 460, undetectable viral load, haemoglobin 13.4 g/dL, platelets 210,000. Generalised bleeding on probing with 4–5 mm pockets.
Show answer and explanation
Correct answer: D. Glycaemic status over the preceding six months
- A. No fasting is required, which is one of the practical advantages of HbA1c over a fasting plasma glucose.
- B. Two to three months is exactly right — this is the standard description of what the test represents.
- C. An HbA1c of 6.5 percent or above on two occasions is a recognised ADA diagnostic threshold for diabetes; 5.7 to 6.4 percent defines prediabetes.
- D. CORRECT as the exception. HbA1c reflects roughly the preceding TWO TO THREE MONTHS, not six. The window is set by the 120-day lifespan of the red blood cell, and because more recent glucose exposure weights the result more heavily, the last month contributes about half the value.
Note: HbA1c becomes unreliable where red cell turnover is abnormal — haemolytic anaemia and recent transfusion falsely LOWER it, iron deficiency and asplenia falsely RAISE it, and haemoglobinopathies interfere with the assay.
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