The present invention relates to devices, methods and kits for the detection and identification of crystals which may be present in a biological fluid, such as urine from a cat. The device may include a filter and an absorbent material. The fluid may be transferred onto the filter, and fluid passes through the filter and into the absorbent material, thereby isolating crystals on a surface of or within the structure of the filter or membrane. The crystals are then available for staining which will reveal a determining component of the crystals. The device may also include a member for inhibiting backflow from the absorbent material to the filter. The present invention also provides methods for detecting and identifying crystals which may be present in biological fluids. The methods include the steps of isolating the crystals on the surface of or within the structure of a filter or membrane, and contacting the crystals with an indicator which is specific for a determining component of the crystals type. Also provided are kits which include the devices of the present invention, and reagents and other materials necessary to conduct the methods of the present invention.