Endocrine Abstracts

Background: Quantification of 1,25-dihydroxyvitamin D (1,25(OH)₂D) remains challenging because of low circulating concentrations and potent cross-reactivities with steroid-like structures. The most frequent assays for 1,25(OH)₂D testing are still based on RIA format with preliminary extraction. The analytical performances and the turnaround time of analysis (TAT) for these assays are limited. Several novel assays for 1,25(OH)₂D testing are emerging. The aim of our study was therefore to evaluate the analytical performances of a recently developed automated immunoassay for the measurement of 1,25(OH)₂D.

Methods: We evaluated the performances of the LIAISON XL 1,25(OH)₂D assay (DiaSorin), a fully automated immunoassay that uses a recombinant fusion protein for capturing 1,25(OH)₂D. The limit of detection and the within- and between-run imprecision were determined. Method comparison was performed with our routine RIA method and with a reference Liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.

Results: The limit of detection was <5 pg/ml. The within-run coefficients of variation (CV) were 2.6 and 4.4% for 1,25(OH)₂D concentrations of 6.7 and 19.7 pg/ml and the between run CVs were 9.3 and 13.1% for concentrations of 25.4 and 101.1 pg/ml. The automated 1,25(OH)₂D assay was significantly correlated to RIA (r=0.74; P<0.0001) and LC-MS/MS (r=0.9975; P<0.0001). The comparison of the automated assay and RIA revealed through Passing-Bablok regression analysis a slope of 0.86 and an intercept of 14.12. The mean bias observed on the Bland-Altman plot was −2.8 pg/ml. The comparison of automated assay and LC-MS/MS revealed through Passing-Bablok regression analysis a slope of 1.07 and an intercept of −1.87. The mean bias observed on the Bland-Altman plot was −8.2 pg/ml.

Conclusion: The LIAISON XL 1,25(OH)₂D automated assay demonstrated superior analytical performances in comparison to RIA assay and a clear improvement of TAT. Furthermore, we demonstrated a strong agreement between this 1,25(OH)₂D automated assay and a reference LC-MS/MS method.