Aims: Recent progress in PTH assay has revealed that the intact PTH assay kit in current use does not differentiate between the truncated 7-84 PTH molecule and the 1-84 PTH molecule. In our series, we examined the effectiveness of a new PTH assay as a noninvasive method of evaluating severity of uremic hyperparathyroidism.
Methods and materials: Two hundred and seventy hemodialysis (HD) patients recruited from three HD centers were included and divided into subgroups according to the conventional iPTH assay results. Pre-dialysis blood samples were collected and subjected to two different PTH assays: "intact" PTH assay (iPTH) and "whole" PTH (wPTH) assay. Two biochemical markers of bone remodeling were also examined.
Results: In all cases, PTH levels determined by the wPTH assay were in the average 32.3% lower than those determined by the iPTH assay. The difference of the results of the two PTH assay methods, which indicated the portion of 7-84 PTH fragments of the total PTH molecules measured with the iPTH assay, was gradually increased while the severity of uremic hyperparathyroidism increased. Biochemical markers of bone formation/resorption showed a similar change.
Conclusion: The portion of the 7-84 PTH fragments and markers of increased bone turnover increased in proportion to the severity of uremic hyperparathyroidism. This finding disproves the hypothetical role of 7-84 PTH fragments alone as the noninvasive marker of low-turnover bone disease in HD patients.