Accuracy of the FreeStyle Method: Measuring Blood-Glucose by Skin-Prick Blood Extraction From Forearm

Abstract

Objectives. Self-measurement of blood glucose levels by the established monitoring systems is accurate but not readily accepted by patients because the finger prick is painful. A new system which involves blood sample collecting at an alternative and less painful site, the forearm, has been developed to facilitate frequent blood glucose measurement. The purpose of this study was to evaluate the accuracy of this new blood glucose monitoring system: the FreeStyle method. Methods. Venous blood samples were drawn from 93 fasting and 93 nonfasting outpatients with diabetes. Plasma was extracted by a standard laboratory method for glucose measurement. Capillary blood was then obtained from each patient by skin prick on the fingertip and forearm. Blood glucose was measured by two standard blood glucose meters, the Glucometer Elite and the Glucotrend 2, and the FreeStyle system. The data were compared with a reference laboratory method. Each patient was also asked to comment on the pain associated with the skin prick at both sites. The accuracy of self-monitoring systems was evaluated by statistical and clinical analyses. Results. Linear regression analysis of the FreeStyle data from fasting patients revealed an intercept of 9.87 mg/dL, a slope of 0.96, and a correlation coefficient (r) of 0.966. Furthermore, error grid analysis (EGA) demonstrated that all of the data fell within zones A (81%) and B (19%), which define clinically acceptable results. Linear regression analysis of the FreeStyle data from nonfasting subjects revealed an intercept of 26.41 mg/dL, a slope of 0.81, and a correlation coefficient (r) of 0.938. EGA revealed that 81% of the data fell within zone A, 17% within zone B and 2% within zone D. The relative standard deviation (RSD) for FreeStyle was similar to the RSD for the two standard meters and the reference laboratory method. Ninety-seven percent of the patients reported that they experienced less pain from the forearm skin prick than from skin prick at the fingertip. Conclusions. The FreeStyle blood glucose monitoring system which requires forearm skin prick for blood extraction is sufficiently accurate for home use. However, caution must be taken because of its potential failure to detect hypoglycemia and because the accuracy is reduced during rapid change of blood glucose levels.