Factors influencing the derivation and clinical application of blood calcium adjustment equations

Area of Science:

• Clinical Chemistry
• Biochemistry
• Laboratory Medicine

Background:

• Laboratories often derive local adjusted calcium (adjCa) equations using patient data and specific exclusion criteria to account for calcium metabolism abnormalities.
• The impact of these exclusion criteria on the final adjCa equation formula and patient results remains unclear.
• This study aimed to investigate how reducing exclusion criteria affects adjCa equations and patient outcomes compared to a reference equation.

Purpose of the Study:

• To evaluate the influence of varying exclusion criteria on the derivation of adjusted calcium (adjCa) equations.
• To compare adjCa equations derived with fewer exclusions against a reference equation.
• To assess the impact of different adjCa equations on patient categorization (hypo-, normo-, or hypercalcaemia).

Main Methods:

• A reference adjCa equation was established using data from 1305 individuals meeting strict exclusion criteria.
• Seven alternative adjCa equations were derived using progressively fewer exclusion criteria, including one with no exclusions.
• All derived equations were applied to a validation cohort of 19,640 patients to assess their effect on adjCa results and calcium status categorization.

Main Results:

• Most alternative adjCa equations, even those with no exclusions, showed no statistically significant difference in slope or intercept compared to the reference equation.
• No patient in the validation cohort exhibited a clinically significant difference (>5% and >0.1 mmol/L) in adjCa results when using alternative equations versus the reference.
• The categorization of patients' calcium status (hypo-, normo-, or hypercalcaemia) remained consistent across all tested adjCa equations.

Conclusions:

• The majority of exclusion criteria used in deriving adjCa equations have minimal impact on the equation itself or the resulting patient adjCa values.
• Even equations derived without any exclusions perform comparably to those with extensive criteria.
• These findings suggest that the process of developing local adjCa equations can be simplified, potentially facilitating wider adoption.