PTH and chronic kidney disease: Here, we examined the association between serum Ca levels within a physiological range and change in kidney function or eGFR in a non-CKD (CKD stages 1 and 2) general Japanese population, in consideration with multiple factors known to be associated with kidney function, and also with those involved in Ca metabolism (i.e. serum levels of inorganic phosphorus (InP), PTH, and 1,25-dihydroxyvitamin D (VitD)).