Improved method for calculating calcium fractions in plasma: reference values and effect of menopause

Area of Science:

• Biochemistry
• Clinical Chemistry

Background:

• Calcium homeostasis is crucial for physiological functions.
• Accurate measurement of ionized calcium (Ca2+) is vital in clinical settings.
• Factors influencing calcium levels, particularly in postmenopausal women, require further investigation.

Purpose of the Study:

• To identify plasma components related to total calcium in postmenopausal women.
• To develop a predictive model for ionized calcium (Ca2+) using total calcium and other plasma constituents.
• To analyze the different fractions of calcium in various demographic groups.

Main Methods:

• Multiple linear regression analysis was employed to determine relationships between total calcium and plasma components.
• A regression equation was formulated and validated to calculate ionized calcium (Ca2+).
• Calcium fractions (protein-bound, ultrafiltrable, complexed) were calculated for different study cohorts.

Main Results:

• Total calcium showed significant positive correlations with albumin, globulin, anion gap, and bicarbonate in postmenopausal women.
• The derived regression equation demonstrated good correlation (r = 0.78, P < 0.001) for calculating ionized calcium (Ca2+).
• Increased plasma calcium in postmenopausal women was attributed to a higher complexed calcium fraction, linked to elevated bicarbonate and anion gap.

Conclusions:

• Plasma albumin, globulin, anion gap, and bicarbonate are significant determinants of total calcium in postmenopausal women.
• The developed regression model provides a reliable method for estimating ionized calcium (Ca2+) from readily available measurements.
• Changes in complexed calcium, influenced by bicarbonate and anion gap, play a key role in elevated plasma calcium observed in postmenopausal women.