Considering the potential benefits of renoprotective nutritional treatment in cats in preazotemic stages of kidney disease, early diagnosis of kidney disease is critical. Symmetric dimethylarginine (SDMA) increases as glomerular filtration rates decrease, with a mean time of 17 months before serum creatinine elevations are observed. However, little is known about the influence of comorbidities on SDMA in cats. Human models have shown that SDMA may be influenced by other diseases. This study examined possible relationships between SDMA and hypertrophic cardiomyopathy and diabetes mellitus. In cats, SDMA does not appear to be affected by hypertrophic cardiomyopathy. However, diabetes mellitus appears to lower SDMA levels, making it a less predictable marker for cats with concomitant diabetes mellitus and chronic kidney disease.