High prevalence of adynamic bone disease diagnosed by biochemical markers in a wide sample of the European CAPD population

Background. Adynamic bone disease (ABD) has been described in the current dialysis population to have an unexpectedly high prevalence. Moreover, it is clearly more prevalent in CAPD patients, compared to haemodialysis patients. Recently we demonstrated that both a low (less than or equal to 27 U/l) level of bone alkaline phosphatase (BAP) as determined by an optimized agarose gel electrophoretic technique and a low (less than or equal to 150 pg/ml) level of iPTH are good markers of AED with sensitivities of 78.1% and 80.6% and specificities of 86.4% and 76.2% respectively. Methods. In this study (n = 212), the prevalence of ABD in the European CAPD population was evaluated by means of these biochemical markers. Clinical data on the patients included were recorded at the moment of blood sampling. In patients under CARD treatment for longer than 9 months, we calculated an index of calcium exposure through PD fluid. Results. In this population with a low exposure to aluminium, the prevalence of ABD as indicated by either a low level of BAP or PTH was 43%. The following risk factors could be identified: advanced age, shorter time on renal replacement therapy, male gender, and high calcium content of PD fluid. The index of calcium exposure was significantly higher in the patients with low BAP and low iPTH levels compared to those with either BAP >27 U/l or iPTH >150 pg/ml. The latter finding gives further support to the hypothesis that a high calcium load administered to renal failure patients may lead to 'oversuppressed' parathyroids in ABD. In a subgroup of patients with a high level of BAP associated with a low iPTH level a profile previously shown to be associated in the presence of aluminium overload, significantly higher serum aluminium levels were noted, suggesting that even in patients with low exposure to aluminium, this element still can affect bone metabolism. Conclusion. A high prevalence of ABD - as diagnosed by biochemical markers - was observed in the European CAPD population. A number of risk factors could be put forward. The aetiology and pathogenesis of this type of renal osteodystrophy remain to be elucidated, but appear, however, to be multifactorial.