What is the difference between ionized calcium (iCa) and calcium levels? How does this relate to electrolyte replacement? 

About one-half of the total calcium exists in the blood in its free ionized form, and about one-half exists in its protein-bound form, mostly with albumin. Measurements of serum calcium include both of these laboratory values. Because ionized calcium is not impacted by the variability of albumin levels, measurements of ionized calcium allow for more accurate calcium replacement therapy if needed (Mosby’s Manual of Diagnostic and Laboratory Tests. 2002;146-150). — Jiajoyce R. Conway, DNP, FNP-BC, NP-C