Pyridinium crosslinks in patients on haemodialysis and continuous ambulatory peritoneal dialysis

BACKGROUND: The urine excretion of the pyridinium crosslinks of collagen,pyridinoline (PYD) and deoxypyridinoline (DPD) closely reflectbone resorption and their assay has been used as specific markersof mature collagen turnover. The aims of this study were toevaluate the use of these markers to predict the severity ofosteodystrophy in patients with chronic renal failure. METHODS: Using an isocratic ion-paired reverse-phase high-performanceliquid chromatography, PYD and DPD were determined in the serum,urine and dialysate of 48 patients with chronic renal failureundergoing haemodialysis (n=28) or continuous ambulatory peritonealdialysis (n=20). Nineteen apparently healthy subjects were studiedas controls. RESULTS: In all groups, serum and urine crosslinks excretion showed poorcorrelation with age. In the patients urine PYD/creatinine andDPD/creatinine were significantly (P0.03 and 0.001 respectively)higher than normal; urine PYD and DPD levels were highly correlatedwith each other (r=0.98) and with serum PTH (r=0.84 and 0.83respectively). The mean (SD) predialysis serum PYD, 269 (334)nmol/l, was significantly (P0.003) elevated compared with normalpatients, 4.1 (0.6) and pre-dialysis serum DPD was 82.9 (93.7)nmol/l. DPD was below the detection limit of the assay in normalsera. In the patients postdialysis decreases in serum PYD andDPD were statistically significant (P<0.0002 and P<0.0007respectively). PYD and DPD were found in the dialysate of patientson haemodialysis as well as 24-h dialysate in patients on CAPD.Dialysate PYD and DPD were highly correlated with each other(r=0.80) and with dialysate creatinine (r=0.76 and r=0.62 respectively).In the patients, the mean serum, urine and dialysate PYD andDPD increased with the duration on dialysis. These findingsconfirm that metabolic bone disease increases in patients withduration of chronic renal failure. CONCLUSION: Estimation of serum crosslinks levels has potential as an additionaltool in the diagnosis and monitoring of renal osteodystrophy.The ability to determine crosslink levels in serum and dialysateshould be particularly useful in patients who are unable toproduce urine.