Validation of an equation for free calcium estimation: accuracy improves after adjustment for phosphate and CO 2

Free calcium is the gold standard for diagnosis of calcium disorders, although calcium assessment is routinely performed by albumin-adjusted calcium. Our objective was to develop a novel-specific correction equation for free calcium employing serum total calcium and other analytes. Retrospective sin...

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Published in:International urology and nephrology 2022-03
Main Authors: Ramirez-Sandoval, Juan C, Diener-Cabieses, Pablo, Gutiérrez-Valle, Fabián, Ley-Tapia, Sofía, Pastrana-Brandes, Santiago, Galindo, Pablo E, Fagundo, Reynerio, Moreno-Yañez, Mauricio, Reza-Albarrán, Alfredo Adolfo, Correa-Rotter, Ricardo
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Language:English
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Summary:Free calcium is the gold standard for diagnosis of calcium disorders, although calcium assessment is routinely performed by albumin-adjusted calcium. Our objective was to develop a novel-specific correction equation for free calcium employing serum total calcium and other analytes. Retrospective single-center cohort study. A new equation for free calcium assessment was formulated from data of hospitalized patients (n = 3481, measurements = 7157) and tested in a validation cohort (n = 3218, measurements = 6911). All measurements were performed simultaneously from the same blood draw. Total CO and phosphate, in addition to albumin, were the principal factors associated to calcium misdiagnosis. A novel laboratory-specific prediction equation was developed: free calcium (mmol/L) = 0.541 + (total calcium [mmol/L] *0.441) - (serum albumin [g/L] *0.0067) - (serum phosphate [mmol/L] *0.0425) - (CO [mmol/L] *0.003). This new equation substantially improved adjusted R to 0.67 (95% CI 0.78-0.82, p 
ISSN:1573-2584