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To the Editor:

I read with much attention and a great deal of interest the editorial by Dr. Elvira Fernández1 on whether the aims of the K/DOQI guidelines on mineral metabolism disorders in stages 3-5 chronic kidney disease are unachievable or inadequate. Dr. Fernández concludes that the recommended values are adequate but unachievable at the time the OSERCE I study was conducted, since no drugs such as oral paricalcitol, sevelamer carbonate or lanthanum carbonate were available for use in pre-dialysis.

However, I believe that the evidence on the adequacy of the mineral metabolism parameter values is not clearly defined by any prospective study as the KDIGO guidelines demonstrate: neither are stage 3 and 4 parathyroid hormone values clear, nor is it clear whether or not we should maintain 25(OH)D values > 30ng/ml or whether or not we should use non-calcium chelating agents in pre-dialysis. The study by Block GA et al.2 on the effects of phosphorus chelating agents in moderate renal failure using calcium and non-calcium chelating agents is very disturbing, given the association between high levels of phosphorus and mortality. The conclusion of that study was that phosphorus chelating agents significantly lowered serum and urinary phosphorus and slowed the progression of secondary hyperparathyroidism in patients with moderate chronic renal failure (CRF) with normal or near normal levels of phosphorus, but that it nevertheless promoted progression of vascular calcification, which called into question the effectiveness and safety of phosphorus chelating agents in stage 3-4 CRF. We require well-designed comprehensive prospective studies that use hard endpoints such as total and cardiovascular mortality to assess what mineral metabolism values are adequate and what interventions can be carried out to achieve them safely.

Conflicts of interest

The author declares potential conflicts of interest.

Lecture fees: Abbot; Sanofi.

Council Membership: Consejo de Metabolismo Mineral de la Asociación Nefrológica de Buenos Aires.