Facilitated determination of ionized calcium

Area of Science:

• Clinical Chemistry
• Biochemistry
• Medical Diagnostics

Background:

• Accurate determination of ionized calcium ([Ca2+]) is vital for managing critically ill patients.
• Previous methods for measuring [Ca2+] in blood samples have limitations.
• Standard anticoagulants can interfere with accurate calcium level measurements.

Purpose of the Study:

• To evaluate the reliability of measuring ionized calcium ([Ca2+]) in whole blood using a calcium-containing heparin preparation.
• To compare whole-blood [Ca2+] measurements with serum [Ca2+] levels.
• To assess the stability of whole-blood [Ca2+] under specific storage conditions.

Main Methods:

• Ionized calcium ([Ca2+]) was measured in whole blood from 120 healthy donors and 50 intensive-care patients.
• A calcium-containing heparin preparation was used for anticoagulation.
• Measurements were performed using a calcium-selective electrode.
• Whole-blood samples were stored anaerobically on ice for up to 2 hours.
• Comparisons were made with serum [Ca2+] and samples treated with calcium-free heparin.

Main Results:

• The mean whole-blood [Ca2+] in healthy donors was 1.23 mmol/L (SD 0.04).
• A very good correlation (r = 0.95) was observed between serum and whole-blood [Ca2+] in intensive-care patients (mean 1.15 mmol/L).
• Storing whole-blood samples anaerobically on ice for 2 hours did not alter [Ca2+] levels.
• Calcium-free heparin preparations significantly decreased measured [Ca2+].

Conclusions:

• Calcium-containing heparin is a suitable anticoagulant for accurate ionized calcium ([Ca2+]) determination in whole blood.
• Whole-blood measurement of [Ca2+] using this method is stable and reliable.
• This approach simplifies sample handling and facilitates rapid therapeutic decisions for critically ill patients.