Background: Testing the potential influence of interfering substances on the measurement performance of needle sensors for continuous glucose monitoring (CGM) is a challenging task. For proper function, the sensors need an almost stable fluidic environment. Previously published in vitro interference experiments were measuring under static concentration conditons. Our experimental setup allows for interference testing with dynamic changes of the interferent concentrations. Methods: We designed a macrofluidic test stand that is fueled by several high-pressure liquid chromatography (HPLC) pumps generating programmable glucose and/or interferent gradients in phosphate-buffered saline (PBS). After optimizing experimental parameters (channel dimensions, temperature, flow rates, gradient slopes, buffer, pH etc.), we validated the setup using Dexcom G6 (G6) and Freestyle Libre 2 (L2) sensors with/without interferents, and using YSI 2300 Stat plus as the reference glucose device at room temperature. Results: Both sensors tracked the programmed glucose changes. After calibration, G6 results closely matched glucose reference readings, while L2 routinely showed ~50% to 60% lower readings, most likely because of the factory-based calibration and temperature compensation. Gradients of maltose, acetaminophen, and xylose were employed to further validate the setup. As expected, both sensors were not affected by maltose. We confirmed previous findings regarding susceptibility of G6 readings to acetaminophen and L2 readings to xylose. Signals from both sensors are influenced by temperature in a linear fashion. Conclusions: Our experimental in vitro setup and protocol may provide a useful method to dynamically test CGM sensors for interfering substances. This may help to improve the accuracy of future CGM sensor generations.

Background: The Sencell sensor (Lifecare AS, Bergen, Norway) uses glucose induced changes in an osmotic pressure chamber for continuous measurement of glucose concentrations in the subcutaneous tissue. A close to linear correlation between the raw sensor signal and the glucose concentration and a very long duration of use (of up to 6-12 months or longer) are theoretically to be expected. The final device is planned to have the size of a grain of rice and to be implanted employing wireless energy and data transfer. Method: For a first clinical proof of concept study in humans, a wired version of the core sensing technology was embedded into a 4 mm needle and inserted into the abdominal subcutaneous tissue of healthy volunteers. The study was conducted to collect first human proof-of-concept performance data for algorithm development during meal experiments and for further device optimization. The raw data was analyzed after one-point calibration and minor trend correction in comparison to the Statstrip blood glucose meter and the Freestyle Libre 2 glucose sensor. Results: Seven participants (5 female, 2 male, age: 49±11 years) delivered a total of 105 direct comparator data-points (vs. Statstrip blood glucose meter) during repeated meal experiments with observation periods between 2 h and up to 72 days. The osmotic-pressure sensor followed glucose changes similar to the FreeStyle Libre device and reached an MARD of 9.8% in comparison to StatStrip (87 % and 13 % of the datapoints were lying in zones A and B of the consensus error grid, respectively). Conclusions: In this first human proof-of-concept study, the osmotic-pressure based continuous glucose sensor was shown to track s.c. glucose concentrations in a comparable manner as the Libre 2 needle sensor. The clinical performance characteristics of the first wired prototypes provide an encouraging perspective for the upcoming next development steps. Disclosure A. Pfützner: Consultant; Novo Nordisk A/S, Research Support; LifeScan Diabetes Institute, Speaker's Bureau; AstraZeneca, Stock/Shareholder; Lifecare A/S, Diakard. M. Hanna: None. N. Thomé: None. H. Jensch: None. Funding Lifecare AS (LIFC-SEN-001)