Tissue fluid measurement device

A method for determining a change in cell volume with a sensor device having four electrodes. The method comprises the following steps: ⋅applying a current with a known cycle of different known frequencies in time series on an outer pair of electrodes; measuring a resulting variating potential over an inner pair of electrodes; ⋅calculating a total impedance absolute value from said measured potential; ⋅storing each total impedance against frequency value in a memory; ⋅reading a frequency value belonging to at least one impedance value of a subsequent cycle; ⋅reading a frequency value belonging to the same at least one impedance value of a previous cycle; ⋅comparing said frequency values and determining a difference between the frequency values; and ⋅providing a time series of differences in frequency across said time series, an increasing frequency difference across said time series indicating a relative increase or decrease of cell volume.