Evaluation of Serum β-Carboxy-Terminal Cross-Linking Telopeptide of Type I Collagen as Marker of Bone Resorption in Chronic Hemodialysis Patients

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.