Facts and artefacts regarding correlation between skin electrical impedance spectroscopy (EIS) and blood glucose

Earlier observations on possible co-variation between skin EIS and blood glucose prompted us to map and include other factors at play in the predictive model. Skin pH would be one such factor. A cohort of 20 diabetics was investigated, taking around 30 measurements spread over each of two different days 2-21 days apart. Each measurement comprises skin EIT in the frequency range 1kHz to 2.5MHz, skin pH, and immediately evaluated blood samples. There is a co-variation for some, but not all, test persons. The relationship gets stronger on the group level by adding pH-information, but is still poor or non-existent for some test persons. Non-invasive EIS measurements on skin is influenced by skin hydration, blood glucose, skin pH, body location, season, environmental factors, and variables not yet understood. Since impedance related parameters are used to estimate skin hydration, users of such devices should be aware that skin pH may influence as much as the water content of the stratum corneum.