Glycated Hemoglobin A1c Levels Are Not Affected by Critical Illness

Objectives: Glycated hemoglobin A1c is used to estimate glycemic control. However, its value upon ICU admission may be altered by critical illness and not reflect true glycemic status. We assessed the relationship between ICU admission glycated hemoglobin A1c and premorbid glycated hemoglobin A1c levels. Design: Retrospective observational cohort study. Setting: Two tertiary ICUs in Australia. Patients: Cohort of 69 critically ill patients with diabetes and glycated hemoglobin A1c levels measured upon ICU admission and during the month prior to admission. Interventions: Measurement of glycated hemoglobin A1c. Measurements and Main Results: Mean (so) glycated hemoglobin A1c level was 7.5% (1.8%) upon ICU admission and 7.8% (2.0%) in previous measurements from the preceding 30 days. The change in glycated hemoglobin A1c did not correlate with time elapsed between the two measurements (r(2) = 0.00005; p = 0.95), but there was a strong correlation between admission glycated hemoglobin A1c levels and premorbid glycated hemoglobin A1c levels (r(2) = 0.89; p < 0.001). Conclusions: Glycated hemoglobin A1c levels are not altered by the onset of critical illness. Glycated hemoglobin A1c quantified at ICU admission can, therefore, be used to reliably estimate chronic glycemic control and guide acute glycemic therapy.