Influence of nutritional status on serum large N-truncated PTH, but not PTH(1–84) in hemodialysis patients

Abstract

Background Serum level of parathyroid hormone (PTH), measured by second-generation intact PTH (I-PTH), is known to be associated with nutritional status in hemodialysis (HD) patients. We investigated whether PTH(7–84) and larger N-truncated PTH or PTH(1–84) might be affected by nutritional status in HD patients. Methods Serum PTH was determined in 170 male HD patients by either a Bio-intact PTH (Bio-PTH) or I-PTH assay. Lean body mass in the trunk region was measured as a nutritional marker by dual X-ray absorptiometry. Results The serum PTH(7–84) level was theoretically obtained from the difference between serum I-PTH and Bio-PTH because I-PTH assay cross-reacted with PTH(7–84) with the same degree as PTH(1–84), although N-truncated PTH fragment larger than PTH(7–84) might affect theoretical serum PTH(7–84) level, although slightly. Serum PTH(1–84) was directly obtained from the serum Bio-PTH value because of its exclusive reaction with PTH(1–84). Serum PTH(7–84) correlated significantly with nutritional markers such as body weight, albumin, protein catabolic rate (PCR), TACBUN, BUN, phosphate, and lean body mass in the trunk, whereas PTH(1–84) correlated only with phosphate. Multiple regression analysis revealed that PCR, body weight, and lean body mass in the trunk region are significant factors independently associated with PTH(7–84), but not with PTH(1–84). Conclusions The results suggest that serum levels of PTH(7–84) and larger N-truncated PTH fragments, but not PTH(1–84), might be affected by the nutritional state in HD patients, which might explain the reported correlation of serum I-PTH levels with nutritional markers.