The study of 216,000 ICU patients found high blood sugar linked to an increase in death risk among certain patients, and that the risk varied according to disease type.
"The increased deaths associated with hyperglycemia in intensive care units was highest in those without diagnosed diabetes and in those admitted with cardiovascular disorders, such as heart attacks, unstable angina, and strokes," said study author Dr. Mercedes Falciglia, assistant professor of medicine at the University of Cincinnati College of Medicine Division of Endocrinology in Ohio.
Even a very slight increase in blood sugar -- as little as one milligram per deciliter above normal -- increased the risk of mortality, the study showed. Risk was highest in stroke patients at 15 times greater than normal in patients with the highest blood sugar readings. High blood sugar did not appear to increase the risk of death in ICU patients with COPD or liver failure, researchers said.
"These findings suggest that different disease states are variably affected by hyperglycemia, with the strongest association in individuals with cardiovascular disorders," said Falciglia.
Falciglia's team calculated a patient's risk of death by evaluating their diagnosis, other health problems, test results and age using a mathematical formula, and then recalculated their risk to include the duration of their hospitalization.
Although previous studies have linked high blood sugar to increased risk of death of hospitalized patients, attempts to control blood sugar with insulin have received mixed results -- some studies did note improvements, while others showed no difference in mortality with insulin therapy.
"Based on the outcome of this large study, we believe that the variable results of those studies may be due to the unique ways that high blood glucose may or may not affect mortality in different types of diseases -- which can be uniquely revealed through large and diverse databases such as those generated by the network of Veterans Affairs hospital ICUs," said Falciglia.
"This effect seen was also greatest in patients without diagnosed diabetes, a finding that deserves further study, because it is not clear why hyperglycemia occurs in hospitalized patients who do not have diagnosed diabetes nor why they may have worse outcomes in some cases than people with diagnosed diabetes," Falciglia added.
Results of the study were presented at the American Diabetes Association's annual Scientific Sessions, in Washington, D.C.