Aqueous and serum-based materials compared for use as simulated calibrators for three ionized calcium analyzers

Area of Science:

• Clinical Chemistry
• Analytical Chemistry
• Biomedical Instrumentation

Background:

• Ionized calcium measurements are critical in clinical diagnostics.
• Inter-analyzer bias can affect the accuracy of ionized calcium results.
• Standardization of ionized calcium analyzers is an ongoing challenge.

Purpose of the Study:

• To evaluate control fluids for decreasing bias between different ionized calcium analyzers.
• To identify optimal reference materials for calibrating ionized calcium measurement devices.

Main Methods:

• Analyzed 10 control fluids using three different ionized calcium analyzers (Radiometer ICA 1, Nova 8, AVL 980).
• Simulated recalibration using between-instrument differences of control fluids during analytical runs.
• Tested control materials with over 150 serum and whole-blood samples.

Main Results:

• A filtered human serum pool (1 mmol/L ionized calcium, CO2 removed, no buffer) consistently reduced bias for both serum and whole blood.
• Another serum pool (1.3 mmol/L ionized calcium, 10 mmol/L bicarbonate) was effective for serum but less so for whole blood.
• Some pH buffering additives negatively impacted calcium ion electrode accuracy and precision.

Conclusions:

• A suitable reference material for ionized calcium analyzers should be tested across multiple instruments and sample types (serum and whole blood).
• Human serum pools demonstrated effectiveness in minimizing analyzer bias.
• Future reference materials should aim to be at least as effective as the tested human serum pools.