Journal Article

A formula to predict corrected calcium in haemodialysis patients

Arsh Jain, Shelly Bhayana, Meghan Vlasschaert and Andrew House

in Nephrology Dialysis Transplantation

Published on behalf of European Renal Association - European Dialysis and Transplant Assoc

Volume 23, issue 9, pages 2884-2888
Published in print September 2008 | ISSN: 0931-0509
Published online April 2008 | e-ISSN: 1460-2385 | DOI: http://dx.doi.org/10.1093/ndt/gfn186
A formula to predict corrected calcium in haemodialysis patients

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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

Journal Article.  3052 words. 

Subjects: Nephrology

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