NDT Advance Access originally published online on September 11, 2007
Nephrology Dialysis Transplantation 2007 22(11):3354-3355; doi:10.1093/ndt/gfm619
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Reply
Correspondence and offprint requests to: Email: yamakazu{at}xqb.biglobe.ne.jpSir,
We thank Dr Joki for his comments on our recent paper [1]. As he summarizes, we consider the excess calcium transferred into patients from the dialysate as one of the causes of vascular calcification in maintenance haemodialysis (HD) patients. However, we need further studies to determine whether using a dialysate with the lower calcium concentration (for examples, 2.5 mEq/l of dialysate calcium) might reduce the acute changes of serum Ca associated with HD and prevent the progression of vascular calcification.
As Dr Joki points out, changes in serum Ca should be expressed as changes in ionized or albumin-corrected Ca because dialysis ultrafiltration induces haemoconcentration and increases albumin levels. Unfortunately, we did not preserve blood samples used in this study, and therefore we cannot measure serum ionized Ca or albumin-corrected Ca just after HD session. However, we revised the value of albumin just after HD (corrected post-HD Alb) by using a concentration rate of dialysis ultrafiltration and calculated albumin-corrected Ca just after HD (corrected post-HD Ca). Using these corrected pre-HD and post-HD Ca values, we again performed a step-wise multivariate regression analysis and confirmed that the result was nearly the same as the previous one, analysed by non-corrected Ca values.
In our subjects, step-wise multiple regression analysis has revealed that acute changes of the serum calcium concentration before and after HD (
Ca) was negatively and positively associated with pre-HD Ca and ultrafiltration, respectively. Therefore, we agree with Dr Joki that a low pre-HD serum Ca and an excessive ultrafiltration should be avoided in HD, in order to prevent the loading of calcium from the dialysate, as we mentioned in the ‘Discussion’ section. However, the increase of the aortic calcification index per year (ACI/year) was significantly associated with Ca and CRP, but not pre-HD Ca and ultrafiltration in the step-wise multiple regression analysis. Thus, we concluded that the increase of serum Ca immediately after HD was related to the rate of progression of aortic calcification. In addition, almost patients in this study showed normocalcaemia just before HD, which may explain why we could not clarify the relationship between progression of vascular calcification and hypercalcaemia or hypocalcaemia, as previously reported [2,3].
As for the dialysate calcium concentration, we believe that Ca overload during HD must occur in some patients treated with a 3.0 mEq/l of dialysate calcium, while Ca loss in association with dialysis ultrafiltration may occur in the other patients. In maintaining appropriate serum levels of Ca and phosphate using various phosphate binders and vitamin D analogues, an adjustment to the dialysate calcium concentration might be needed [4]. At present, it remains undetermined whether or not a dialysate calcium concentration of 2.5 mEq/l as recommended by the K/DOQI guidelines [5] is preferred for almost HD patients. More research is warranted to determine the optimal dialysate calcium level.
Conflict of interest statement. None declared.
First Department of Internal Medicine
Miyazaki Medical College
University of Miyazaki
Miyazaki, Japan
References
- Yamada K, Fujimoto S, Nishiura R, et al. Risk factors of progression of abdominal aortic calcification in patients on chronic haemodialysis. Nephrol Dial Transplant (2007) 22:2032–2037.
[Abstract/Free Full Text] - Cozzolino M, Dusso AS, Slatopolsky E. Role of calcium-phosphate product and bone-associated proteins on vascular calcification in renal failure. J Am Soc Nephrol (2001) 12:2511–2516.
[Free Full Text] - Floege J, Ketteler M. Vascular calcification in patients with end-stage renal disease. Nephrol Dial Transplant (2004) 19([Suppl 5]):V59–V66.[CrossRef][Medline]
- Toussaint N, Cooney P, Kerr PG. Review of dialysate calcium concentration in hemodialysis. Hemodial Intern (2006) 10:326–337.[CrossRef]
- National Kidney Foundation. K/DOQI clinical practice guidelines for bone metabolism and disease in chronic kidney disease. Am J Kidney Dis (2003) 42(Suppl 3):S1–S201.[Medline]
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