PTH and chronic kidney disease: Elevations in serum PTH and FGF23, which are stimulated in healthy subjects by increased P intake and which are increased in patients with established CKD, are associated with increased risk of CKD progression6, 61 Likewise, in cats, elevations in sPi, PTH and FGF23 are risk or prognostic factors for all‐cause mortality and progression of CKD.55, 62, 63, 64, 65