HIF1A and chronic kidney disease: The objectives are as follows: (1) to evaluate the concentrations of HIF-1α in the plasma and urine (pHIF-1α/uHIF-1α), as well as the concentrations of NTBI in urine (uNTBI), using both healthy cats and cats with CKD; (2) to investigate the correlations between the concentrations of HIF-1α and NTBI in biofluids.