Urinary collagen cross-links to evaluate hyperparathyroidism in kidney transplant patients

Abstract

INTRODUCTION AND AIMS: One of most common complication following kidney transplantation is reappearance of hyperparathyroidism (HP) some months after normal serum levels. An early diagnosis represents the best prophylaxis measures to prevent worsening of osteodystrophy and potential damage to the graft and vascular tissue.The aim to our study was to evaluate, beyond the common HP markers, if the urinary cross-links of the collagen PYD (pyridinoline) and DPD (Deoxypyridinoline) are useful markers able to show increasing levels of parathormone. METHODS: We evaluated 50 stable kidney transplanted patients divided into 2 group (A: 38 pts and B: 12 pts) dependent on the type of their immunosuppressive therapy (Cyclosporine A and mycophenolate mophetil with or without corticosteroids). RESULTS: All patients showed elevated levels of urinary cross-links even though calcemia and phosphoremia values were normal and creatinine level slightly increased.( Table 1) A statistically significant correlation was found between PYD and ALP (alkaline phosfathase) (p=0.0026), PYD and DPD (p=0.015), pre- and post- kidney transplantation iPTH (intact parathyroid hormone) (p=0.024), and creatinine and ALP (p=0.024). Post kidney transplantation iPTH values were moderately elevated. No significant correlation was found between urinary cross-links and the other parameters. Taking the groups separately, while a significant correlation between PYD and ALP (p=0.0076), PYD and DPD (p=0.017), ALP and post transplant iPTH (p=0.038), OC (osteocalcin) and post transplant iPTH (p=0.048), and pre- and post-transplant iPTH (p=0.019) was found in subjects belonging to group A, subjects of group B showed a correlation between post-transplant iPTH and age at transplantation (p=0.032).(Table 2.) CONCLUSIONS: Our results showed that urinary cross-links could play a role in revealing bone reabsorption in kidney transplanted patients when usual bone metabolism parameters do not demonstrate a state of HP.