Response to "Low Turnover Bone Disease in Early CKD Stages".

The Authors Reply:

Barreto et al. wrote a letter titled, “Low Turnover Bone Disease in Early CKD Stages” in response to our manuscript, “Low Turnover Renal Osteodystrophy With Abnormal Bone Quality and Vascular Calcification in Patients With Mild-to-Moderate CKD.”

Our results confirm prior reports (including that of Barreto et al.) of lower bone turnover at milder reductions of glomerular filtration rate compared with more progressed loss of kidney function. However, the report by Barreto et al. reveals histomorphometric data with high osteoclastic surface that is not fully supportive of the diagnosis of low bone turnover. Furthermore, the finding of very high mineralization lag times requires explanation. The same patients were first reported by Tomiyama et al. They were selected for various reasons, including cardiovascular disease. This raises the question of immobilization influencing histomorphometric results.

We have carefully ruled out patients with any abnormalities known to affect bone turnover to ensure that changes observed are only related to reduced kidney function. We had more Whites and older patients than Barreto et al.

The 1996 article by Coen et al. found only 9 of 76 patients with chronic kidney disease with adynamic bone disease at a creatinine clearance of 19.5 ± 11.9 ml/min. Patient selection criteria were not given. Neto et al. found more patients in the normal bone histology group than in any other.

Thus, our patient population is different from those studied in prior publications. We have cited the more recent publications. Confirming prior publications is important and aids in the acceptance of the data by the scientific and clinical community.

Fourier-transform infrared spectroscopy has not been done before on bone samples from this patient population. We did not intend to present Fourier-transform infrared spectroscopy as a routine clinical diagnostic tool. We agree that currently it is mainly a research method, but it adds valuable information on bone quality which cannot be obtained by histomorphometry. The measured mineral-to-matrix ratio is a key parameter of bone composition and has been found to be related to bone stiffness and energy to fracture. Our manuscript provided references for further information on this novel tool for assessment of bone quality.