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Related Experiment Videos

Serum ionised calcium concentration: measurement versus calculation.

S C Conceicao, D Weightman, P A Smith

    British Medical Journal
    |April 29, 1978
    PubMed
    Summary

    Direct measurement is essential for accurate serum ionized calcium levels. Calculated values, especially in renal failure or transplant patients, are unreliable and do not substitute for direct testing.

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    Area of Science:

    • Clinical Chemistry
    • Nephrology

    Background:

    • Accurate measurement of serum ionized calcium is crucial for patient management.
    • Previous studies have explored methods for calculating ionized calcium from total calcium and protein levels.

    Purpose of the Study:

    • To compare the accuracy of calculated serum ionized calcium concentrations with direct measurements.
    • To evaluate the reliability of indirect methods across different patient populations.

    Main Methods:

    • Serum samples from 47 normal volunteers, 104 chronic renal failure patients, and 83 renal transplant recipients were analyzed.
    • Serum ionized calcium was directly measured using an Orion SS-20 meter.
    • Calculated ionized calcium was derived using three formulae and a nomogram based on total calcium and protein concentrations.

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    Main Results:

    • Direct measurement and calculated values showed good agreement in normal subjects and hemodialysis patients.
    • Poor agreement was observed in conservatively treated renal failure patients and transplant recipients.
    • Indirect methods misclassified a significant percentage of patients with abnormal measured ionized calcium levels.

    Conclusions:

    • Calculation of serum ionized calcium is not a reliable substitute for direct measurement.
    • Clinical decisions should not be based solely on calculated ionized calcium values, particularly in specific patient groups.