An automated system for filtration of a sample and for rare cell detection of a sample, the system comprising: a filtration apparatus comprising a membrane through which the sample is passed to provide a retentate suspected of having a quantity of rare cells; a fluid delivery apparatus that introduces a fluid onto the membrane for filtration or detection of the rare cells; a pressure sensor disposed on or about the membrane to directly or indirectly indicate a level of fluid on the membrane, wherein the fluid is a liquid, the automated system being characterized in that it further comprises an electronic control circuit configured to: a) determine an actual time lapsed for a known quantity of fluid to pass through the membrane from a starting time to a point in time, the point in time being determined when the the pressure sensor indicates a pressure less than, or within a set amount from a predetermined threshold value; b) determine a theoretical time for a known quantity of fluid to travel through the membrane from the starting time to the point in time, wherein a difference between the theoretical time and the actual time is indicative of a more rapid than expected loss of the fluid; c) determine the adjustment amount of the fluid to add to the membrane from the fluid delivery apparatus based upon the difference between the actual time and the theoretical time; and d) direct the fluid delivery apparatus to add the adjustment amount to the membrane. a filtration apparatus comprising a membrane through which the sample is passed to provide a retentate suspected of having a quantity of rare cells; a fluid delivery apparatus that introduces a fluid onto the membrane for filtration or detection of the rare cells; a pressure sensor disposed on or about the membrane to directly or indirectly indicate a level of fluid on the membrane, wherein the fluid is a liquid, the automated system being characterized in that it further comprises an electronic control circuit configured to: a) determine an actual time lapsed for a known quantity of fluid to pass through the membrane from a starting time to a point in time, the point in time being determined when the the pressure sensor indicates a pressure less than, or within a set amount from a predetermined threshold value; b) determine a theoretical time for a known quantity of fluid to travel through the membrane from the starting time to the point in time, wherein a difference between the theoretical time and the actual time is indicative of a more rapid than expected loss of the fluid; c) determine the adjustment amount of the fluid to add to the membrane from the fluid delivery apparatus based upon the difference between the actual time and the theoretical time; and d) direct the fluid delivery apparatus to add the adjustment amount to the membrane. a) determine an actual time lapsed for a known quantity of fluid to pass through the membrane from a starting time to a point in time, the point in time being determined when the the pressure sensor indicates a pressure less than, or within a set amount from a predetermined threshold value; b) determine a theoretical time for a known quantity of fluid to travel through the membrane from the starting time to the point in time, wherein a difference between the theoretical time and the actual time is indicative of a more rapid than expected loss of the fluid; c) determine the adjustment amount of the fluid to add to the membrane from the fluid delivery apparatus based upon the difference between the actual time and the theoretical time; and d) direct the fluid delivery apparatus to add the adjustment amount to the membrane.