Although we previously found a positive association of plasma XOR activity with serum uric acid level in subjects who underwent health examinations as well as patients receiving hemodialysis treatments10–12, an inverse association of renal function with serum uric acid level independent of plasma XOR activity was also been revealed in our other results11,12, suggesting that the balance of serum uric acid level and plasma XOR activity might be different between individuals with and without CKD/ESRD. This evidence concerns the gene XDH and chronic kidney disease.