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

Area of Science:

• Critical Care Medicine
• Clinical Chemistry
• Biochemistry

Background:

• Low ionized calcium (ICa) is common in critical care patients.
• Standard methods using albumin-corrected total calcium (cTCa) often fail to detect ICa accurately.
• These methods do not account for changes in calcium complexation with anions.

Purpose of the Study:

• To evaluate if adjusting total calcium (TCa) for anion complexation improves the diagnosis of low ICa.
• To compare the effectiveness of anion gap (AG) and its components (Ion model) in predicting low ICa.

Main Methods:

• Retrospective analysis of intensive care unit patients with measured ICa.
• Development of logistic and linear models to predict and estimate ICa using AG or its components.
• Validation of models using arterial and venous gas panels.

Main Results:

• Anion gap (AG) and its components were significant predictors of low ICa.
• The logistic Ion model demonstrated superior diagnostic accuracy (ROC area 0.92 ± 0.02) compared to the AG model (0.89 ± 0.02) and cTCa (0.81 ± 0.03).
• Linear models for ICa estimation lacked clinical precision.

Conclusions:

• Adjusting TCa for AG or its components significantly enhances the diagnosis of low ICa.
• This improved diagnostic approach may guide further ICa testing in critical care settings.