There is growing interest in alternative less painful sites for capillary blood glucose (CBG) monitoring. The earlobe tip is a potential site (1) that has been occasionally used by nurses when fingertip testing is refused or difficult. We investigated the clinical value and accuracy of earlobe CBG measurements as an alternative to fingertip and forearm testing.
A total of 50 patients with type 2 diabetes (aged 42–82 years, 28% with neuropathy) were enrolled in the study. The duration of diabetes was 9.5 ± 8.3 years (means ± SD). Testing sites (lateral aspect of the fingertip, earlobe tip, and flexor surface of the forearm) were rubbed and cleaned before lancing was performed by a physician using Lifescan Unistick-2 lancets (Lifescan, Milpitas, CA). The forearm was lanced using the Microlet-Vaculance device (Bayer, Tarrytown, NY). The order of site testing was randomized. Pain was immediately assessed after the first attempt using a 100-mm graphic visual scale (2). CBG was measured with an Accu-Check Advantage glucose meter (Roche, Indianapolis, IN).
First-attempt sampling success rates were 88% (fingertip), 74% (earlobe), and 62% (forearm). After earlobe pricking, bleeding lasted for <60 s in all subjects (<30 s in 90%). Earlobe pain (median score 5.5 mm) was less uncomfortable than fingertip pain (17 mm, P < 0.01, Wilcoxon test) but not statistically different from forearm (8.0 mm). Although earlobe pain was more tolerable, a limitation in this study is that it did not evaluate pain perception after repeated testing on multiple days, when skin soreness might become relevant.
CBG measurements from the earlobe deviated from the fingertip by 9.5 ± 1.0% (mean ± SE). The correlation coefficient between these two sites was 0.97 (P < 0.01). Of earlobe measurements, 97.8% were within clinically acceptable zones A+B by error grid analysis (3). When earlobe was compared with forearm, CBG deviation was 10 ± 1.4%, correlation coefficient 0.96 (P < 0.01), and 95.3% of measurements were within zones A+B by error grid analysis.
In contrast to other sites that require vacuum-assisted lancing devices or sophisticated glucose meters, our observations demonstrate that CBG monitoring at the earlobes is attainable with regular standard lancets and that earlobe CBG concentrations correlate well and deviate minimally from either fingertip or forearm values. Earlobe testing was also clinically accurate by the error grid analysis method, which takes into account the effects on the clinical decision that would have been made if the CBG had been measured in the reference site. These data support the notion that earlobe CBG concentrations can be used in substitution of fingertip values. However, one limitation in our data series is that glucose values <70 mg/dl were not observed. Therefore, earlobe testing should be avoided if hypoglycemia is suspected.
For many patients, the earlobe pricking technique may be less convenient because it requires a second person to lance the skin and collect the blood. This certainly limits the applicability of the technique in the outpatient setting. Nevertheless, earlobe testing seems to be a useful alternative that could minimize costs and discomfort in patients assisted by a relative or nurse in hospitals and nursing homes.
