Case-control Investigation of Previously Undiagnosed Diabetes in the Critically Ill

CONTEXT: The outcome of patients requiring intensive care can be influenced by the presence of previously undiagnosed diabetes (undiagDM). OBJECTIVE: This work aimed to define the clinical characteristics, glucose control metrics, and outcomes of patients admitted to the intensive care unit (ICU) with undiagDM, and compare these to patients with known DM (DM). METHODS: This case-control investigation compared undiagDM (glycated hemoglobin A(1c) [HbA(1c)] ≥ 6.5%, no history of diabetes) to patients with DM. Glycemic ratio (GR) was calculated as the quotient of mean ICU blood glucose (BG) and estimated preadmission glycemia, based on HbA(1c) ([28.7 × HbA(1c)] – 46.7 mg/dL). GR was analyzed by bands: less than 0.7, 0.7 to less than or equal to 0.9, 0.9 to less than 1.1, and greater than or equal to 1.1. Risk-adjusted mortality was represented by the Observed:Expected mortality ratio (OEMR), calculated as the quotient of observed mortality and mortality predicted by the severity of illness (APACHE IV prediction of mortality). RESULTS: Of 5567 patients 294 (5.3%) were undiagDM. UndiagDM had lower ICU mean BG (P < .0001) and coefficient of variation (P < .0001) but similar rates of hypoglycemia (P = .08). Mortality and risk-adjusted mortality were similar in patients with GR less than 1.1 comparing undiagDM and DM. However, for patients with GR greater than or equal to 1.1, mortality (38.5% vs 10.3% [P = .0072]) and risk-adjusted mortality (OEMR 1.18 vs 0.52 [P < .0001]) were higher in undiagDM than in DM. CONCLUSION: These data suggest that DM patients may develop tolerance to hyperglycemia that occurs during critical illness, a protective mechanism not observed in undiagDM, for whom hyperglycemia remains strongly associated with higher risk of mortality. These results may shed light on the natural history of diabetes.