A simple method for determining physiologically active calcium and magnesium concentrations in critically ill...

Area of Science:

• Clinical Chemistry
• Critical Care Medicine
• Electrolyte Balance

Background:

• Total serum calcium and magnesium levels are often abnormal in critically ill patients, even when ionized levels are normal.
• Ionized calcium and magnesium are the biologically active forms, crucial for various physiological processes.
• Existing methods for measuring ionized levels may not always be accessible in critical care settings.

Purpose of the Study:

• To evaluate the accuracy of ultrafilterable serum calcium and magnesium concentrations in critically ill patients.
• To determine if ultrafilterable levels can reliably predict ionized hypocalcemia and hypomagnesemia.
• To assess ultrafilterable calcium as an alternative to direct ionized calcium measurements.

Main Methods:

• Analysis of total serum calcium and magnesium concentrations.
• Measurement of ultrafilterable serum calcium and magnesium concentrations.
• Comparison of ultrafilterable levels with ionized calcium and magnesium levels in critically ill patients.

Main Results:

• Ultrafilterable serum calcium was highly sensitive (95%) and specific (93%) for predicting ionized hypocalcemia.
• Total serum calcium showed high sensitivity (93%) but low specificity (50%) for ionized hypocalcemia.
• Total serum magnesium demonstrated high sensitivity (100%) but moderate specificity (73%) for ultrafilterable hypomagnesemia.

Conclusions:

• Ultrafilterable calcium concentrations serve as a dependable alternative to ionized calcium measurements when ion-selective electrodes are unavailable.
• Ultrafilterable magnesium levels may provide a more accurate reflection of true ionized magnesium concentrations compared to total serum magnesium values.
• These findings support the clinical utility of ultrafilterable mineral assays in critical care settings.