PTH and chronic kidney disease: Previous UK recommendations were in concordance with the original KDIGO guideline from 2009 and suggest that treatment is considered if PTH levels are persistently above the upper reference limit for the assay in patients with CKD 3b–5 and above 9 times the upper limit of normal for patients on dialysis, suggesting that treatment is modified in order to keep PTH levels between 2 and 9 times the upper limit of normal in dialysis patients.