Abstract and Introduction
Abstract
Background In patients with acute coronary syndrome (ACS), increased plasma glucose levels are associated with worse outcome. Our aim is to ascertain the values of admission and fasting glucose for prediction of death among patients with ACS; and to compare their predictive capacities.
Methods The relationships of mortality to plasma glucose levels among 811 consecutive patients hospitalized with ACS were estimated using spline Cox models. Blood samples were obtained upon admission and after overnight fast. The predictive capacities of fasting and admission glucose were compared using time-dependent receiver operating characteristic curves.
Results Fasting and admission glucose levels were higher among the 151 patients who died (18.6%) than among survivors (P < .001). Among the 558 patients with no history of diabetes (68.8%) there was a J-shaped dependence of the all-time mortality hazard ratio on fasting glucose that persisted when adjusted for covariates: hazard was lowest at 110 mg/dL (6.1 mmol/L), and significantly greater at levels <90 mg/dL (5.0 mmol/L) or >117 mg/dL (6.5 mmol/L). Likewise among non-diabetic patients, the predictive capacities of admission and fasting glucose were similar for forecast times of up to about 1 year, but for later times the area under the receiver operating characteristic curve was larger for fasting glucose than admission glucose (P < .05). Neither admission nor fasting glucose levels discriminated among diabetic patients in regard to risk of death.
Conclusions Both admission and fasting glucose may be used for triage of nondiabetic ACS patients; fasting glucose may additionally be useful for long-term management, for which the relationship with the all-time mortality hazard ratio is J-shaped.
Introduction
Alterations of glucose metabolism are common among patients admitted to hospital with acute coronary syndrome (ACS), regardless of whether diabetes mellitus has been diagnosed previously. ACS patients may present with hyperglycemia during the acute period (admission hyperglycemia) and/or exhibit hyper- or hypoglycemic fasting plasma glucose levels during hospitalization. These alterations have variously been associated with larger infarct size, a greater incidence of congestive heart failure, cardiogenic shock, and both short- and long-term mortality.
Admission hyperglycemia, which some studies have found to be associated with less risk for patients with a previous history of diabetes than for those without, has been reported to reflect or be associated with a stress-induced increase in insulin resistance and other stress responses. Fasting glucose is more related to the background metabolic state, depending not only on tissue insulin sensitivity but also on the state of complex hormonal and metabolic networks.
Most previous comparisons of the prognostic values of admission and fasting glucose have considered death and survival rates at just one fixed time post-admission or by the end of follow-up, without attempting to determine how prognostic value may depend on forecast time. However, taking forecast time dependence into account might be useful in clinical decision-making: in principle it is possible that while the acute event (admission hyperglycemia) may strongly predict short-term risk, the parameter more closely related to background metabolism (fasting glucose) may be a more sensitive predictor of the maintenance of a high risk level over time.
In the present study we aimed to ascertain and compare the abilities of admission and fasting glucose to predict the death of ACS patients, distinguishing between those with and those without a previous diagnosis of diabetes mellitus. The nonlinear relationships between glucose levels and risk of death were modeled by means of cubic spline Cox analyses, and the predictive values of admission and fasting glucose were characterized for forecast times of up to 4 years by means of time-dependent receiver operating characteristics (ROCs), a technique that as far as we know has not previously been employed in this context.