Hyperglycaemic index as a tool to assess glucose control: a retrospective study

Abstract

Introduction: Critically ill patients may benefit from strict glucose control. An objective measure of hyperglycaemia for assessing glucose control in acutely ill patients should reflect the magnitude and duration of hyperglycaemia, should be independent of the number of measurements, and should not be falsely lowered by hypoglycaemic values. The time average of glucose values above the normal range meets these requirements.

Methods: A retrospective, single-centre study was performed at a 12-bed surgical intensive care unit. From 1990 through 2001 all patients over 15 years, staying at least 4 days, were included. Admission type, sex, age, Acute Physiology and Chronic Health Evaluation II score and outcome were recorded. The hyperglycaemic index (HGI) was defined as the area under the curve above the upper limit of normal (glucose level 6.0 mmol/l) divided by the total length of stay. HGI, admission glucose, mean morning glucose, mean glucose and maximal glucose were calculated for each patient. The relations between these measures and 30-day mortality were determined.

Results: In 1779 patients with a median stay in the intensive care unit of 10 days, the 30-day mortality was 17%. A total of 65,528 glucose values were analyzed. Median HGI was 0.9 mmol/l (interquartile range 0.3-2.1 mmol/l) in survivors versus 1.8 mmol/l (interquartile range 0.7-3.4 mmol/l) in nonsurvivors (P < 0.001). The area under the receiver operator characteristic curve was 0.64 for HGI, as compared with 0.61 and 0.62 for mean morning glucose and mean glucose. HGI was the only significant glucose measure in binary logistic regression.

Conclusion: HGI exhibited a better relation with outcome than other glucose indices. HGI is a useful measure of glucose control in critically ill patients.

Figure 1

Calculation of the hyperglycaemic index (HGI). All measured glucose values (black dots) and their corresponding sampling times are taken into account. The average over time is calculated for the area (shaded) under the glucose curve for hyperglycaemic values only. The normal glucose range is indicated by the hatched area, with 6.0 mmol/l (dotted line) the cutoff. HGI is the shaded area divided by the total length of stay. In this case HGI is 0.73 mmol/l, as indicated by the dashed line. Note that normal or hypoglycaemic measurements do not affect HGI, and thus they do not falsely lower this index.

Figure 2

Receiver operator characteristic (ROC) curves for different glucose measures. HGI, hyperglycaemic index.

Figure 3

Relation between hyperglycaemic index (HGI; divided into quartiles) and mortality. In the highest quartile mortality is nearly three times higher than mortality in the lowest quartile (P < 0.001).

Figure 4

Hyperglycaemic index (HGI) for various glucose cutoffs. The cutoff in all other analyses was chosen at 6 mmol/l because it was the upper limit of the intensive treatment group in the Leuven study [4,5]. To see how HGI performs at other cutoff values, the area under the ROC curve was determined for HGI cutoffs from 4.0 to 15.0 mmol/l. In the patients studied, a cutoff between 6.0 and 8.0 mmol/l was associated with the greatest area.