Serum Levels of 1–84 and 7–84 Parathyroid Hormone in Predialysis Patients with Chronic Renal Failure Measured by the Intact and Bio-PTH Assay

Abstract

Background: The intact parathyroid hormone (PTH) assay detects both PTH(1–84) and the PTH(7–84)-like fragment, which is reported to be an antagonist of the biological action of PTH(1–84). It is debatable which of the two assays is clinically more useful, the intact or bio-PTH assay, the latter of which only detects PTH(1–84). It is also unknown whether serum levels of the PTH(7–84)-like fragment have clinical significance. Methods: Serum PTH concentrations in 104 predialysis patients with chronic renal failure (CRF; serum creatinine 3.53 ± 1.93; 62 males and 42 females; 61.0 ± 11.5 years old) were measured using both the intact and bio-PTH assays, and the concentration of the PTH(7–84)-like fragment was calculated by subtracting bio-PTH from intact PTH. Three bone formation and three bone resorption markers were measured simultaneously. Results: The PTH values measured using the two assays were strongly positively correlated (r = 0.959, p < 0.0001), and were also significantly positively correlated with the three bone formation and three bone resorption markers to a similar degree. The PTH(7–84)-like fragment was significantly positively correlated with both the intact and bio-PTH (r = 0.855, p < 0.0001 for intact PTH; r = 0.672, p < 0.0001 for bio-PTH), and was also significantly positively correlated with each of the six bone metabolism markers. There is no significant relationship between the bio-PTH/PTH(7–84)-like fragment ratio and clinical parameters including bone metabolic markers. Conclusion: From the strong relationship between the two assays, and the similar degree of the relationship between each PTH assay and each of the six bone metabolism markers, it is considered that the bio-PTH and intact PTH assays have similar clinical significance in predialysis CRF patients. Serum levels of the PTH(7–84)-like fragment seem to increase as serum PTH(1–84) increases. The results suggest that the serum PTH(7–84)-like fragment has little specific clinical effect on bone metabolism, even when assessed by the ratio of bio-PTH/PTH(7–84)-like fragment.