Pyridinium crosslinks in patients on haemodialysis and continuous ambulatory peritoneal dialysis

The urine excretion of the pyridinium crosslinks of collagen, pyridinoline (PYD) and deoxypyridinoline (DPD) closely reflect bone resorption and their assay has been used as specific markers of mature collagen turnover. The aims of this study were to evaluate the use of these markers to predict the severity of osteodystrophy in patients with chronic renal failure.

Using an isocratic ion-paired reverse-phase high-performance liquid chromatography, PYD and DPD were determined in the serum, urine and dialysate of 48 patients with chronic renal failure undergoing haemodialysis (n = 28) or continuous ambulatory peritoneal dialysis (n = 20). Nineteen apparently healthy subjects were studied as controls.

In all groups, serum and urine crosslinks excretion showed poor correlation with age. In the patients urine PYD/creatinine and DPD/creatinine were significantly (P < or = 0.03 and < or = 0.001 respectively) higher than normal; urine PYD and DPD levels were highly correlated with each other (r = 0.98) and with serum PTH (r = 0.84 and 0.83 respectively). The mean (SD) predialysis serum PYD, 269 (334) nmol/l, was significantly (P < or = 0.003) elevated compared with normal patients, 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 normal sera. In the patients postdialysis decreases in serum PYD and DPD were statistically significant (P < 0.0002 and P < 0.0007 respectively). PYD and DPD were found in the dialysate of patients on 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 and DPD increased with the duration on dialysis. These findings confirm that metabolic bone disease increases in patients with duration of chronic renal failure.

Estimation of serum crosslinks levels has potential as an additional tool in the diagnosis and monitoring of renal osteodystrophy. The ability to determine crosslink levels in serum and dialysate should be particularly useful in patients who are unable to produce urine.