Beyond the Numbers: Assessing Clinical Risk Associated with Significant Magnesium Assay Bias

Background: Analytical variability in magnesium (Mg) assays is widely recognized, yet distinguishing its impact from intrinsic clinical risk remains under-emphasized in laboratory training. Methods: A routine delta check identified atypical Mg result shifts, prompting investigation and retesting on an alternate analyzer. Analytical error magnitude was quantified using absolute and percent difference and total allowable error (TE_a), with clinical relevance assessed through integrated analytical verification, agreement analysis, and patient-level risk stratification. Results: A lapse in delta check containment allowed continued reporting after initial error detection. Root cause analysis (RCA) identified Mg reagent contamination and incomplete cuvette drying, causing carryover and positive bias. Among 93 samples, 59 were impacted, with deviations reaching 147.4%, and 63% (59/93) exceeded TE_a. Despite substantial analytical bias, clinical impact was limited: 27% (16/59) remained within the reference interval and 53% (31/59) had ≤3.5 mg/dL, requiring no urgent attention. The remaining 20% (12/59) were >3.5 mg/dL, and 11/12 lacked an Mg-elevating condition (e.g., chronic kidney disease (CKD)) and required no intervention. The single CKD patient had persistently elevated Mg levels before and after correction, with no effect on interpretation, management, or monitoring. All affected results were corrected and communicated to providers. Only 1/59 (~2%) required follow-up monitoring, with no definite cause identified. Conclusions: This investigation demonstrates that the significance of analytical error is defined as much by clinical context as magnitude. The study identifies assay-specific and system-level vulnerabilities, particularly a gap between error detection and response. These findings underscore the need for integrated analytical, clinical, and operational safeguards and formalizing these competencies within training programs to improve laboratory quality, reliability, and practice consistency.