Effects of parathyroidectomy on plasma iPTH, (1-84)PTH and (7-84)PTH levels in patients with stage 5 chronic kidney disease

Objective Currently, parathyroid hormone (PTH) is mainly measured by the second generation intact PTH (iPTH) assay which detects both full-length (1-84)PTH and (7-84)PTH fragments. The third generation whole PTH (wPTH) assay however has turned out to be specific for (1-84)PTH. The aim of this study is to investigate the features of plasma iPTH, (1-84)PTH, (7-84)PTH levels in patients with stage 5 chronic kidney disease (CKD), and evaluate the effects of parathyroidectomy (PTX) on above markers in severe secondary hyperparathyroidism (SHPT) patients. Methods A cross-sectional study including 90 controls and 233 stage 5 CKD patients, and a prospective follow-up study in 31 severe SHPT patients were conducted. Plasma iPTH and (1-84)PTH levels were measured by the second and third generation assay, respectively. Circulating (7-84)PTH level was calculated by subtracting the (1-84)PTH value from the iPTH value. Results Plasma levels of iPTH, (1-84)PTH, (7-84)PTH were higher (P＜0.01), and (1-84)PTH/iPTH was lower (P＜0.01) in stage 5 CKD patients than in controls. For severe SHPT patients with PTX (n=74), plasma iPTH, (1-84)PTH and (7-84)PTH concentrations were significantly increased compared to non-PTX group (n=159) (P＜0.01), and the increase of (7-84)PTH level was more striking than (1-84)PTH. Meanwhile, the value of (1-84)PTH/iPTH was decreased (P＜0.01). Plasma iPTH level was strongly correlated with (1-84)PTH level (r=0.980, P＜0.01) in stage 5 CKD patients. Also, both iPTH and (1-84)PTH levels were positively correlated with serum alkaline phosphatase, dialysis vintage and serum phosphorus (P＜0.01). After PTX (median interval of follow-up: 7.1 months), plasma iPTH, (1-84)PTH, (7-84)PTH concentrations were decreased (by 92.9%, 89.7%, 95.8%, P＜0.01, respectively) greatly and (1-84)PTH/iPTH was increased (P＜0.01). Conclusions In stage 5 CKD patients, plasma iPTH, (1-84)PTH, (7-84)PTH levels are greatly increased while (1-84)PTH/iPTH is decreased, and PTX can significantly improve abnormality of above markers in severe SHPT patients. The second generation PTH assay overestimates the severity of SHPT, and the accurate measurement of (1-84)PTH by the third assays is more conducive to diagnosis and treatment of CKD and SHPT patients.