Abstract: An apparatus and method for concentrating and measuring low levels of cells in biological samples. The apparatus, or concentration device, consists of two chambers with an optically level collection membrane intermediating between the chambers. The collection membrane filters the biological sample, trapping cellular elements of interest. A vacuum may be attached to the device to assist in filtration. The surface area of the collection membrane matches the view field of a standard imaging system and the device can be mounted on a standard microscope stage. All the cells in the sample volume are collected onto the membrane. The view field provides a fixed volumetric area for cell counting. Since the volume of sample tested is known, the total number of cells in the original sample may be calculated. The sample reservoir of the concentration device may also be used for sample preparation.