Hyperthyroidism is a common ailment of older cats. The presence of hyperthyroidism can make it difficult to determine whether or not a cat has another common ailment, loss of kidney function. One common treatment for hyperthyroidism is radioactive iodine, and the treatment typically includes a weeklong hospital stay. Kidney problems, masked by the hyperthyroid state and discovered only after treatment, may make the cat ill, may require chronic treatment, and can reduce life expectancy. The aim of this project is to discover a measurable component of a hyperthyroid cat’s urine that is associated with hidden kidney failure. To do this, the team will apply mass spectrometry, a technique that is capable of identifying thousands of urine components. The long-term goal is to devise a test to accurately assess the presence of hidden kidney problems in hyperthyroid cats before treatment is undertaken, thus maximizing the chances for a successful outcome.