NDT Advance Access published online on April 3, 2008
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfn186
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A formula to predict corrected calcium in haemodialysis patients
1 Division of Nephrology, Department of Medicine 2 Department of Epidemiology and Biostatistics, University of Western Ontario, London Health Sciences Centre, London, UK 3 Division of Endocrinology and Metabolism, University of Calgary, Canada
Correspondence and offprint requests to: Arsh Jain, Division of Nephrology, Department of Medicine, Epidemiology and Biostatistics, University of Western Ontario, London Health Sciences Centre, London, UK. Tel: +44- 519-685-8500 Ext 55726; Fax: +44-519-685-8072; E-mail: arsh.jain{at}utoronto.ca
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Abstract |
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Background. The conventional calcium correction formula (corrected total calcium (mmol/L) = TCa (mmol/L) + 0.02 [40 (g/L) – albumin (g/L)]) is broadly applied for the estimation of serum calcium in haemodialysis (HD) patients, despite the fact that it was not derived or validated in a HD population. A novel formula was derived and validated for corrected serum calcium in HD patients.
Methods. Total calcium (TCa), ionized calcium (iCa2+), magnesium, phosphate, albumin and bicarbonate were collected from 60 HD patients to derive the formula. A validation set of 237 stable HD patients was then examined, and subjects were classified as hyper-, hypo- and normocalcaemic based on the iCa2+. Agreement of the new formula was calculated with iCa2+ as the gold standard, using the intraclass correlation coefficient (ICC). This was compared to the agreement between iCa2+ and the following: uncorrected total serum calcium (TCa), the conventional correction formula, the Orrell formula and the Clase formula.
Results. Using multiple linear regression the following formula was derived: corrected total calcium (mmol/L) = TCa (mmol/L) + 0.01 [30 (g/L) – albumin (g/L)]. The new formula had superior agreement compared to all of the other formulae. There was a statistically significant greater agreement between the new formula and the iCa2+ as compared to the conventional formula (P < 0.01). However, the new formula did not significantly outperform the Orrell formula, the Clase formula or Total calcium.
Conclusions. The use of our simple new formula should enable more appropriate decision making compared to the conventional formula in the highly complex HD population.
Keywords: corrected calcium; haemodialysis; ionized calcium; serum calcium
Received for publication: 5.12.07
Accepted in revised form: 10. 3.08
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