An automated ‘bio-intact’ PTH assay: a step towards standardisation and improved correlation with parathyroid function in renal disease

Abstract

Background: Most methods for the determination of parathyroid hormone (PTH) show cross-reactivity with N-truncated forms of PTH. The analytic and diagnostic value of a recently developed automated PTH test without this cross-reactivity was examined. Methods: The PTH levels of 73 patients undergoing hemodialysis were compared using the ‘bio-intact’ PTH (Nichols Institute Diagnostics) and 3 ‘intact’ PTH tests (from Nichols, Roche Elecsys® and Diagnostics Corporation DPC). Further, the (non 1–84) PTH fragment and the PTH ratio (bio-intact PTH/(non 1–84) PTH) were calculated. All results were then correlated with biochemical bone markers (bone-specific alkaline phosphatase and bone collagen C-terminal telopeptides in serum). Results: ‘Bio-intact’ PTH values were lower than the PTH results generated by the ‘intact’ PTH assays. Results of all PTH tests were closely correlated ( r=0.96–0.98, p<0.01). Correlations with biochemical bone markers were high ( r=0.31–0.63, p<0.01), but no significant association between the PTH ratio and all other tests ( r=−0.2 to 0.03) was found. Conclusions: In stable hemodialysis patients, the different PTH tests show a similar correlation with the bone markers. It is however desirable to measure PTH with assays devoid of any cross-reaction for a better comparability. In this study, the PTH ratio was not correlated with biochemical bone markers; the use of this ratio requires further investigation.