PTH and chronic kidney disease: In a study of 3879 patients with CKD from the Chronic Renal Insufficiency Cohort (CRIC), Isakova et al. observed that (i) the level of serum FGF23 rose as the estimated glomerular filtration rate (eGFR) declined, and (ii) rises in serum FGF23 and PTH levels preceded hyperphosphatemia; similar results have also been described elsewhere [10,11,12,14].