Comparison of intact and 'whole molecule' parathyroid hormone assays in patients with histologically confirmed post-renal transplant osteodystrophy.

Background: Fragments of parathyroid hormone (PTH) have been identified (amino acids 7-84) which may interfere with commercially available 'intact molecule' PTH assays. Novel assays which employ an antibody directed to the first seven amino acids of the N-terminus of PTH are thought to be free from cross-reactivity with the 7-84 fragments, and therefore measure true 'whole molecule' PTH. Transplant recipients (as well as those in end-stage renal failure) have been reported to have elevated levels of 'intact' in comparison with 'whole molecule' PTH.

Methods: PTH concentrations were assessed in serum samples obtained from female renal transplant recipients previously classified as either having hyperparathyroid (n = 14) or adynamic bone disease (n = 14) by transiliac crest bone biopsy. PTH was measured as 'whole molecule' (Scantibodies 'whole molecule' PTH) and 'intact' (DPC Immulite 2000 intact PTH and Scantibodies total PTH).

Results: Scantibodies 'whole molecule' PTH (all-subject mean 48.7 ng/L, +/- 53.0) were significantly lower than DPC intact (83.5 ng/L, +/- 88.1; P < or = 0.0001) and Scantibodies total PTH (80.5 ng/L, +/- 92.4; P < or = 0.0001). However, the differences between the 'whole molecule' and 'intact' measurements were similar across the two patient groups, and reflected the lower reference range employed by the 'whole molecule' assay.

Conclusion: The 'whole molecule' PTH assay was unable to discriminate between the two patient populations and provided very little additional clinical information to that obtained from the intact PTH assays.