A diagnostic device is described herein that can be used to perform magneto-optical detection and discernment of crystals within a biofluid sample. A magnetic field can be applied by the diagnostic device in a direction relative to light traveling through the sample. The presence of a crystal can be determined based on the magneto-optical properties of the sample. The detected crystal can be one of two similar crystal types that may be in the biofluid sample. The two similar crystal types can exhibit different magneto-optical properties under a magnetic field in a different direction. Accordingly, the type of crystal can be discerned by applying the magnetic field in the different direction as light travels through the sample. Discernment of the type of crystal can lead to diagnosis of the particular disease condition and subsequent proper treatment of the disease condition.