The Effects of Skin Temperature and Testing Site on Blood Glucose Measurements Taken by a Modern Blood Glucose Monitoring Device

BACKGROUND: Modern blood glucose (BG) monitoring devices (e.g., InDuo LifeScan, Inc., Milpitas, CA) require very low blood volumes, allowing for testing at sites other than the traditional fingertip, but the reliability of such testing has not been fully elucidated. The aim of this randomized study was to compare the effects of cold/warm skin temperature combined with alternative site (forearm) testing versus conventional fingertip measurements on fasting and postprandial conditions. MATERIALS AND METHODS: The study population consisted of 19 patients who had previously used InDuo for 6 weeks. Four simultaneous (within 1 min) BG readings (left and right forearm and fingertips) were obtained from each patient 15, 10, and 5 min before eating. Ten minutes before eating, the patient immersed one arm in cold water (15.5 degrees C) and the other in warm water (35 degrees C). At time 0 min arms were removed from water baths, and the patient was offered a standard meal (duration 15 min). Arms were again immersed in water baths, and BG was measured from the same locations 20 min after eating and at subsequent 15-min intervals for 185 min. The effects of site testing and temperature were assessed in this period by identifying maximum BG concentrations (C (max)) and time to C (max) (T (max)). RESULTS: Significantly lower Cmax values were observed for (1) cold forearm versus cold fingertip (mean Delta 28.6 mg/dL, P < 0.001), (2) warm forearm versus warm fingertip (mean Delta 12 mg/dL, P = 0.028), (3) cold fingertip versus warm fingertip (mean Delta 17.2 mg/dL, P = 0.002), and (4) cold forearm versus warm forearm (mean Delta 33.7 mg/dL, P < 0.001). Significantly longer Tmax values were reported for cold forearm versus warm forearm (mean Delta 22.4 min, P < 0.001) and cold forearm versus cold fingertip (mean Delta 20 min, P < 0.001). CONCLUSIONS: These results demonstrate that cold skin and forearm conditions significantly underestimate BG concentrations and delay T(max) compared with warm skin and fingertip measurements.