Methods for measuring agreement: glucose levels in gingival crevice blood

The aim of the present study was to compare conclusions drawn by two different methods for comparison of blood glucose determination in capillary fingerstick blood (CFB) and gingival crevice blood (GCB). Glucose levels in CFB and GCB oozing from the gingiva after periodontal probing were measured in 31 patients with gingivitis or periodontitis using a novel, very sensitive self-monitoring device (Freestyle, TheraSense Inc.) developed for off-finger tip glucose testing. Correlation analysis revealed that measurements of glucose levels in CFB from left and right finger tips were highly correlated pointing to excellent performance of the device, whereas CFB and GCB measurements were moderately, but highly significantly, correlated. A thorough analysis of agreement revealed, on the other hand, questionable performance of the device for screening hypoglycaemic patients. The mean difference of measurements in CFB samples was +3.2+/-12.7 mg/dl. The 95% limits of agreement were -21.7 and +28.2. The mean difference of glucose determination in CFB and GCB samples was -22.0+/-26.6 mg/dl, and limits of agreement were -74.4 and +30.1. By plotting differences on means of measurements and doing linear regression analysis no systematic trend of change in differences with increasing mean of measurements was ascertained. Analysis of agreement revealed that performance of the Freestyle measuring device yielded considerably large limits of agreement, and gingival crevice blood cannot be recommended for measuring blood glucose levels.