Abstract: A method for validating a filter unit. The method includes guiding a fluid flow of a fluid after the fluid flow passed through the filter unit to a measurement area that is connected to the filter unit. The measurement area the fluid is exposed to is at least one alternating electric field between at least two electrodes. The method includes obtaining at least one electric signal between the at least two electrodes. The at least one electric signal is at least affected by whether one or more cells of a plurality of cells in the fluid pass through the measurement area. The method includes determining, at least partially based on the obtained at least one electric signal, at least one validity information indicating a validity of the filter unit.