Limitations of calculated ionised calcium & adjusted calcium in critically ill patients: Time to consider measured ionised calcium
- Author:
Nada Syazana Zulkufli
1
Author Information
1. Division of Laboratory Medicine, Department of Pathology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia
- Collective Name:Farhi Ain Jamaluddin; Tengku Norita Tengku Yazid
- Publication Type:Journal Article
- Keywords:
measured ionised calcium;
estimated ionised calcium;
calculated ionised calcium;
ionised calcium formula;
adjusted calcium
- From:The Malaysian Journal of Pathology
2020;42(3):385-394
- CountryMalaysia
- Language:English
-
Abstract:
Introduction: Ionised calcium is a good prognostic and diagnostic tool as opposed to total calcium
in critical patients but is not available in most central laboratories and non-intensive care units. To
date, four equations to calculate ionised calcium in critical patients have been published. Objectives:
(1) Evaluate the four published equations’ performance in estimating ionised calcium; (2) Determine
the accuracy of calculated ionised and adjusted total calcium in classifying patients according to
calcium states; and (3) Identify factors associated with hypocalcaemia in the critically ill population.
Materials and methods: This is a cross-sectional study involving 281 critically ill patients aged 18-80
years of both genders in a Malaysian tertiary intensive care unit. Performance of the four equations
was analysed using Bland-Altman difference plot and Passing Bablok regression analysis. Crosstabulation was conducted to assess classification accuracy. Mann-Whitney U or Pearson Chi-Square
tests were performed to identify variables associated with hypocalcaemia. Results: Calculated ionised
calcium using all four equations significantly overestimated ionised calcium. Calculated ionised and
adjusted total calcium had poor accuracies in classifying hypocalcaemic patients. pH was significantly
higher in hypocalcaemics. Conclusion: Calculated ionised and adjusted total calcium significantly
overestimate ionised calcium in the critically ill. In this specific population, calcium status should
only be confirmed with ionised calcium measured by direct ion-selective electrode (ISE).
- Full text:5.2020my01085.pdf
