Rapid changes in postprandial blood glucose produce concentration differences at finger, forearm, and thigh sampling sites

OBJECTIVE - To compare pre- and postmeal capillary blood glucose concentrations measured at the finger, forearm, and thigh in adults with diabetes. RESEARCH DESIGN AND METHODS - For phase 1, capillary blood glucose concentrations were measured at six time points (premeal and at similar to60, 90, 120, 150, and 180 min postmeal) using a blood glucose monitoring system and technician-obtained samples collected from finger, forearm, and thigh sites of 42 adults With diabetes. The finger samples were also tested with a laboratory instrument. For phase 2, similar to14 weeks later, the testing procedures were repeated with 38 subjects from the original study population. RESULTS - Meter finger results were accurate at all time points. Alternate sites tended to produce lower glucose readings compared to finger readings at times when glucose was increasing rapidly (60 and 90 min postmeal). Forearm-to-finger differences correlated with rates of glucose change (r = 0.56, P < 0.001), as did the thigh-to-finger differences (r = 0.52, P < 0.001). Other factors, such as subject age, BMI, diabetes type, and insulin dependence did not have a significant impact on site differences. When the testing procedures were repeated with the same subjects, the pattern of site differences was consistent, although individual results were variable. CONCLUSIONS - Changes in blood glucose immediately after a meal may be identified at finger sites before detection at forearm or thigh sites. Alternate site testing appears to be a useful option for routine self-monitoring before meals; however, patients and clinicians should recognize that results may be different from fingertip results when glucose levels are changing rapidly.