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

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.