Many refractometers, such as the one depicted here, has specific gravity scales for urine in cats (left scale) and dogs (middle scale). The third scale is for total protein measurement on serum, plasma or body cavity fluids. The interface between the dark and white areas (refractive line) indicate the refractive index, which is converted to a total protein (or total solids) value in g/L (arrow). This animal had a total protein (solids) of 9.3 g/dL.
