PTH and chronic kidney disease: Studies in CKD patients without vitamin D substitution report PTH levels of 36 (IQR 25, 49) pg/mL or 26.4 (SD 28.11) pg/mL at GFR > 60mL/min/1.73 m2 with up to 185.5 (SD 159.88) pg/mL and 184 (IQR 109, 304) pg/mL at GFR < 30 and <15 mL/min/1.73 m2, respectively [35,36].