Agreement between bedside blood and plasma glucose measurement in the ICU setting

Study objective: To assess the agreement between bedside glucose (bGlu) measurements and laboratory plasma glucose (pGlu) measurements in the ICU setting. Design: Retrospective study. Setting: ICU of a tertiary academic medical center. Patients: One hundred ninety-seven patients admitted to the ICU from January through December 2002 who underwent 816 simultaneous bGlu and pGlu measurements. Interventions: None. Measurements and results: To calculate the agreement between the two methods of glucose measurement, the mean difference was obtained, and the limits of the agreement were calculated as the mean difference +/- 2 SDs. On 767 occasions, the mean bGlu was 159 mg/dL and the mean pGlu was 151 mg/dL (p < 0.001). The mean difference between the two techniques was 7.9 mg/dL (SD, 17.6 mg/dL), and the limits of agreement were + 43.1 and -27.2. On 31 occasions, the bGlu was reported as > 400 mg/dL, and in these cases the mean pGlu was 423 mg/dL (range, 300 to 900 mg/dL). On IS occasions, the bGlu was reported as < 50 mg/dL, and in these cases the mean pGlu was 66.9 mg/dL (range, 13 to 198 mg/dL). Conclusions: On average, bGlu provides a reasonable estimate for pGlu. However, for the individual patient, bGlu gives an unreliable estimate for pGlu. All of those taking care of critically ill patients should be aware of the limitations of bedside glucometry.