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Nephrol Dial Transplant. 2008 Sep;23(9):2884-8. doi: 10.1093/ndt/gfn186. Epub 2008 Apr 3.

A formula to predict corrected calcium in haemodialysis patients.

Author information

1
Division of Nephrology, Department of Medicine, University of Western Ontario, London Health Sciences Centre, London, UK. arsh.jain@utoronto.ca

Abstract

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 (iCa(2+)), 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 iCa(2+). Agreement of the new formula was calculated with iCa(2+) as the gold standard, using the intraclass correlation coefficient (ICC). This was compared to the agreement between iCa(2+) 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 iCa(2+) 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.

PMID:
18388119
DOI:
10.1093/ndt/gfn186
[Indexed for MEDLINE]
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