My senior dog has kidney disease and a fever. What are the causes?

Hi there! Thanks for using Petco Pet Education Center, formerly Petcoach! Glad to talk to a fellow colleague. I think in a case like this the first thing to consider is what is causing the clinical findings. In an older Golden retriever with such a high fever, I would be very concerned about underlying causes that can cause fevers such as for example an upper urinary tract infection such as pyelonephritis which can explain both the fever and the high renal values or possibly cancer. I think further diagnostics that can be pursued include abdominal ultrasound and urine culture and susceptibility. If there is any concern for lymphoma (due to for example the presence of peripheral lymphadenopathy), I would recommend checking an ionized calcium secondary to lymphoma for example as that could explain the increased renal values and potentially the fever. A CBC would also be helpful to try to see if there is an immature neutrophilia for example that could further support an infectious disease though this can also occur due to cancer to some extent. Thorough fluid therapy is important though again, diagnostics to try to pinpoint the cause of the fever would be crucial. If you are unable to proceed with diagnostics and physical examination does not point out any other possible causes, I would consider using broad-spectrum antibiotics such as enrofloxacin and Clavamox. Best of luck! Feel free to get back to use to further discuss this case.