Novel methods of predicting ionized calcium status from routine data in critical care: External validation in MIMIC-III.

Background: Low ionized calcium (I) is prevalent and prognostic in critical care, but poorly detected by either total calcium (T) or albumin-corrected T (cT). We recently derived models of I (Pred-I) and low I (Prob) in critical care that adjust T for binding to albumin and small anions-represented by the anion gap's components. On internal validation, they outperformed cT in diagnosing low I.

Predicting ionized hypocalcemia: External validation of an ionized calcium prediction model in patients with COVID-19 and renal failure.

Background: Ionized hypocalcemia is common in critically ill patients with COVID-19 and is associated with adverse outcomes. We previously developed a linear model that estimates ionized calcium (I) by adjusting total calcium (T) for the three components of the anion gap and albumin. On internal validation, it outperformed the popular method that corrects T for albumin alone (cT) in diagnosing low I.

Predicting Ionized Hypocalcemia in Critical Care: An Improved Method Based on the Anion Gap.

Background: Low ionized calcium (ICa) is prevalent in critical care patients. It is poorly detected by the popular indirect method, which corrects serum total calcium (TCa) for change in albumin. That correction (cTCa) ignores any concomitant change in the anion-complexed fraction of TCa.

Graded interference with the direct potentiometric measurement of sodium by hemoglobin.

Objectives: Sodium concentration is measured by either indirect (I) or direct potentiometry (D), on chemistry and gas panels, respectively. A spurious difference between these methods (ΔNa=I-D) can be confusing to the clinician. For example, variation in serum total protein (TP) is well known to selectively interfere with I.