With respect to information about bone turnover we were not able to find differences between whole PTH and intact PTH assays. Our data also suggest that whole PTH and intact PTH assays give similar information. (i) The correlation between all PTH assays was very high. (ii) The rank order between whole PTH and Nichols intact PTH assays was comparable. (iii) The association between intact PTH assays and non-PTH(1-84) was very high. Albeit non-PTH(1-84) was mostly determined by the prevailing intact PTH concentration, diagnostic information on parathyroid activity provided by whole PTH or intact PTH, respectively, may differ in individual patients. How often this would happen cannot be answered with the currently available data. Unequivocal structural identification of the non-PTH(1-84) fraction would facilitate the answer to that question. The use of the whole PTH/non-PTH(1-84) ratio as a biochemical bone marker in renal bone disease requires further investigation.
Availability of a fast and automatic TRAb assay offers an attractive alternative to the manual TRAb assays for the differential diagnosis of hyperthyroidism.
Background: The carboxy-terminal cross-linking telopeptide of type I collagen (β-CrossLaps, β-CTX) is released into the circulation during degradation of type I collagen and serves as a marker of bone resorption. β-CTX is known to undergo a diurnal rhythm in normal individuals and to accumulate in chronic renal failure. β-CTX has a potential role in noninvasive diagnosis of renal bone disease. Methods: Serum β-CTX was compared to parathyroid hormone (PTH) and other biochemical bone markers in 90 unselected hemodialysis patients. Results: Mean β-CTX was elevated above the normal range (1.72 ± 0.93 µg/l); there were large individual variations. Serum β-CTX was significantly correlated with various PTH assays (r >0.56) and with tartrate-resistant acid phosphatase 5b (TRACP 5b, r = 0.629), bone-specific alkaline phosphatase (r = 0.404) and osteocalcin (r = 0.534, all correlations p < 0.001). The correlation between β-CTX and PTH was significantly higher than the correlation between TRACP 5b and PTH. Several factors which could confound interpretation of serum β-CTX were assessed in further studies: (i) There was no recognizable influence of the time of blood sampling (morning dialysis shift versus afternoon dialysis shift) on serum β-CTX. (ii) Serum β-CTX was not significantly related to residual diuresis of patients. Conclusions: We found a high association between β-CTX and other established markers of bone and calcium metabolism demonstrating the potential utility of β-CTX as marker of bone resorption in renal bone disease. However, further studies employing bone histology are still warranted to exactly define the influence of glomerular retention on serum β-CTX in end-stage renal disease.
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