Nephrol Dial Transplant (2004) 19: 2153-2154
Nephrol Dial Transplant Vol. 19 No. 8 © ERA-EDTA 2004; all rights reserved
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Email: pablo.urena{at}wanadoo.fr (or urena.pablo.{at}wanadoo.fr)1 Service de Nephrologie-Dialyse, Clinique de L'Orangene 11 Boulevard Anatole France, 93300 Aubervilliers France2 Service Central de Biophysique Laboratoire de Biologie Endocrinienne Hôpital Lariboisière, 2 rue Ambroise Paré, 75475 Pairs Cédex 10 France3 INSERM Unité 349, Hôpital Lariboisière, 2 rue Ambroise Paré 75475 Paris Cédex 10 France4 Scantibodiés Laboratory, Inc., Santec, CA, USA5 Service de Physiologie et Explorations Fonctionelles, Hôpital Bichat, 46, rue Henri Huchard, 75018, Paris, France
Sir,
First, we would like to thank Benyahia et al. for their interest expressed for our recent article [1]. As we have answered Dr Gosh in a recent Nephrology Dialysis Transplantation letter [2], we could not see any difference in the Z-score at the mid-radius between patients with or without skeletal fractures. Only the Z-score at the total body was significantly lower in patients with fractures. However, the number of fractured patients was significantly greater for patients with a Z-score at the mid-radius lower than –2.5 (11/21) compared with those with a Z-score lower than –2.5 at the total body (2/21). Now, when we analysed the data again, according to the authors suggestion, we observed a slightly but significant lower mid-radius bone mineral density (BMD) in the group of patients exhibiting appendicular skeleton fractures compared with patients without fractures, the Z-score was –3.156±1.239 vs –2.137±1.560, respectively (P<0.05). Thus, low bone density at the mid-radius seems associated with appendicular skeleton fractures. However, for an unexplained reason, the Z-score at total body could better discriminate fractures in this small cohort.
Secondly, regarding serum aluminium levels, the distribution was the following: 47 patients had a value between 0.10 and 0.49 µM, 21 patients between 0.49 and 0.88 µM, one patient had 1.27 µM and another patient, recently admitted to our centre and suffering from a serious psychiatric disorders, had 4.0 µM. Indeed, as stated in our article [1], the mean serum aluminium value was 0.48±0.50 µM, which can be considered as a usual value found in most patients dialysed worldwide, and it was not a risk factor of rib fracture in the Cox model.
Thirdly, for >10 years the use of aluminium-containing phosphate binders has definitely been stopped in our centre. There was no difference in the mean serum aluminium concentration between patients with or without rib fractures: 0.47±0.1 vs 0.47±0.5 µM, respectively. As this was a cross-sectional study there was no reliable data concerning the serum aluminium values 5–10 years before the study. However, no prior history of aluminium overload or desferrioxamine treatment was recorded in the present patients at the moment of the study with the exception of the patient mentioned previously.
Fourthly, the Z-score at the lumbar spine of the five patients with a history of vertebral fracture was slightly lower, but not significant statistically, probably because of the low number and the high dispersion of the values, than that of patients without fracture, –1.35±2.59 vs 0.24±2.14, respectively.
The fifth point is that we disagree with the statement that 50% of our patients had a serum parathyroid hormone (PTH) concentration >469 pg/ml. The mean value was 298± 301 pg/ml and 41 out of the 70 patients had a PTH of <233 pg/ml. Moreover, the serum PTH values were normally distributed in this patient population as shown below (Figure 1). Thus, high serum PTH levels are certainly playing a role in the low BMD at the mid-radius but they are not the only factor as we suggested in our article. Other factors that might be involved in this cortical bone loss include age, heparin, anaemia, malnutrition and life style abnormalities. Regarding the daily doses of calcium carbonate, which ranged from 0.5 to 3.0 g/day, we believed we have intuitively been respecting the recent NKF/DOQI recommendations to avoid the installation of a low bone turnover and the devastating cardiovascular calcifications often seen in dialysis patients receiving higher doses of calcium carbonate [3]. No correlation was observed between serum PTH and vitamin D concentrations measured at the end of the winter, mostly during the month of March, in the present dialysis patients. Moreover, we did not find any correlation between the average dose, the cumulative dose or the duration of the treatment with vitamin D with any of the biochemical parameters.
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Our final point is, as suggested, we have looked at the correlation of serum leptin levels with BMD at the total body and lumbar spine after adjustment for body mass index (BMI) and fat mass. The correlation of serum leptin with these parameters was still better after its adjustment for BMI (r = 0.51, P<0.0002 at the total body and r = 0.38, P<0.001 at the lumbar spine). Unfortunately, we did not find any significant correlation between Z-score at the mid-radius and serum leptin concentration even after stratifying the values below and above 17 ng/ml.
References
- Ureña P, Bernard-Poenaru O, Ostertag A et al. Bone mineral density, biochemical markers and skeletal fractures in hemodialysis patients. Nephrol Dial Transplant 2003; 18: 2325–2331
[Abstract/Free Full Text] - Ghosh AK. Bone mineral density in the distal radius and increased risk of fractures in haemodialysis. Nephrol Dial Transplant 2004; 19: 1012–1013
[Free Full Text] - Eknoyan G, Levin A, Levin N. K/DOQI clinical practice guidelines for bone metabolism and disease in chronic kidney disease. Am J Kidney Dis 2003; 42: S1–S201[Medline]
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