RESUMO
Currently, the second-generation intact parathyroid hormone (iPTH) assay is commonly used for measuring PTH levels. The iPTH assay detects both full-length (1-84)PTH and (7-84)PTH fragments, which have antagonistic effects on (1-84)PTH in bones and kidneys. The third-generation PTH assay is specific for (1-84)PTH. This study examined the features of different PTH fragments in stage 5 chronic kidney disease (CKD) and the effects of parathyroidectomy (PTX) on the above markers in severe secondary hyperparathyroidism (SHPT) patients. The cross-sectional study included 262 stage 5 CKD patients and 90 controls. A prospective follow-up study was then conducted in 34 PTX patients. Second- and third-generation assays were used to measure plasma iPTH and (1-84)PTH levels, respectively. Circulating (7-84)PTH levels were calculated by subtracting the (1-84)PTH value from the iPTH value. Different plasma PTH fragments were higher, and (1-84)PTH/iPTH was lower in CKD patients than in controls. Plasma (1-84)PTH and (7-84)PTH concentrations increased as iPTH levels increased, and (7-84)PTH increased more evidently. Plasma iPTH, (1-84)PTH and (7-84)PTH levels were 1530.5 (885.0-2111.5) pg/ml, 683.1 (431.4-1018.0) pg/ml, and 739.3 (452.6-1261.0) pg/ml, respectively, in PTX patients. Plasma iPTH, (1-84)PTH and (7-84)PTH concentrations decreased considerably, and the (1-84)PTH/iPTH ratio increased after PTX (median follow-up interval: 10.9 months). Stage 5 CKD patients had higher plasma levels of different PTH fragments, and lower (1-84)PTH/iPTH ratio. PTX could significantly reverse these abnormalities in severe SHPT patients. The iPTH assay overestimated the function of the parathyroid glands; thus, the third-generation PTH assay is likely better for the management of CKD patients.
