Reference

Equation to estimate free (ionized) calcium from total calcium, phosphorus, albumin and CO2. Formulated from data of hospitalized patients (n = 3481, measurements = 7157) and tested in a validation cohort (n = 3218, measurements = 6911). 

Ramirez-Sandoval JC, Diener-Cabieses P, Gutiérrez-Valle F, et al. Validation of an equation for free calcium estimation: accuracy improves after adjustment for phosphate and CO2. Int Urol Nephrol. 2022;54(10):2625-2635. 

PMID: 35294676.