There is provided a medical device for measuring an analyte concentration in the subcutaneous tissue of a patient, the medical device comprising a body access unit and a processing unit. The body access unit and the processing unit are functionally connected when an analyte concentration is measured. The body access unit comprises a transcutaneous dialysis member for accessing the body of a patient. A fluid reservoir is contained at least partially in the transcutaneous dialysis member, and the fluid reservoir is at least partially bounded by a porous membrane. The fluid reservoir contains an analyte sensitive liquid. The processing unit comprises an excitation means adapted to act on a displacement member of the body access unit to generate a flow of the analyte sensitive liquid in the fluid reservoir. The processing unit further comprises a displacement sensor adapted to measure a displacement behavior of the displacement means, a damping of the displacement behavior caused by at least the viscosity of the analyte sensitive liquid contained in the fluid reservoir.
