Implementation of an Automated Lipoprotein(a) Assay on a Third-Party Automated Analyzer: Validation, Method Comparison, and Clinical Impact of Formula-Based Mass-to-Molar Conversion.

BACKGROUND: Lipoprotein(a) [Lp(a)] is an independent, genetically determined cardiovascular risk factor. Although consensus recommends reporting Lp(a) in molar units using assays with minimized apolipoprotein(a) [apo(a)] isoform size-related bias, some laboratories still use mass units with conversion formulas of uncertain reliability. This study describes the first adaptation and validation of the Roche Tina-quant® Lp(a) Gen.2 assay [TQ-Lp(a)] on the Atellica Solution platform, including method comparison and evaluation of formula-based mass-to-molar conversion. METHODS: A total of 126 serum samples were analyzed using 3 approaches: Roche TQ-Lp(a) as the molar comparator method, adapted Atellica-TQ-Lp(a), and native Siemens Lp(a) on Atellica CH, which reports results in mg/dL. Siemens mass-based results were converted to nmol/L using the manufacturer's equation. Analytical performance was assessed according to Spanish Society of Laboratory Medicine recommendations. Method comparison included Passing-Bablok regression, Bland-Altman, and Cohen κ at clinically relevant thresholds. RESULTS: Atellica-TQ-Lp(a) demonstrated acceptable precision (CV <6%), excellent linearity (r = 0.99), and adequate sensitivity (limit of quantification, 8 nmol/L). No relevant interference was observed, and stability was maintained for 4 days under refrigerated and frozen conditions. Agreement with the comparator method was high (slope, 0.99; intercept, 3.9 nmol/L; r = 0.99), with minimal constant bias and high categorical concordance (weighted κ = 0.98). In contrast, formula-derived values showed proportional bias (slope, 1.27), moderate agreement (weighted κ = 0.78), and frequent upward reclassification at ≥125 nmol/L. CONCLUSIONS: The Roche Tina-quant® Lp(a) Gen.2 assay can be implemented on Atellica CH to report Lp(a) in nmol/L with high analytical comparability to the Roche/cobas implementation. Fixed mg/dL-to-nmol/L conversion formulas introduce systematic bias and clinically relevant misclassification.