Method comparison of three automated 25-hydroxy vitamin D enzyme immunoassays to liquid chromatography tandem mass spectroscopy (LCMS/MS) and against each other.

Nada Rakovan1, Trine Lauritzen1,*, Per Olov Nordstrøm1, Øyvind Skadberg2

1Department of Medical Biochemistry, Drammen hospital, Vestre Viken Hospital Trust, Drammen, 2Department of Medical Biochemistry, Stavanger University Hospital, Stavanger, Norway

Introduction: The most reliable assessment of vitamin D status is measurement of plasma 25-hydroxyvitamin D (25[OH]D) concentration. High variability in 25(OH)D measurements due to utilized test and assay technologies and the lack of standardization against reference materials and reference method often confounds proper assessment of vitamin D status.

Objectives: The objective of the study was to compare the analytical performance of three automated immunoassays for the determination of serum 25(OH)D to liquid chromatography tandem mass spectroscopy (LC-MS/MS) and comparison against each other.

Methods: A total of 113 human serum samples were analyzed with automated immunoassays from Abbott (ARCHITECT i2000), Siemens (ADVIA Centaur®) and Roche (Cobas 6000). The results were compared against a LC-MS/MS used as the reference method as well as to each other.

Results: Passing-Bablok regression analysis demonstrated a slope for each method compared with LC-MS/MS: 0,88 (95 % CI=0,83-0,94) for ADVIA; 1,19 (95 % CI=1,09-1,28) for ARCHITECT; and 1,26 (95 % CI=1,16-1,38) for Cobas. When comparing immunoassays against each other, Passing-Bablok regression slope for Cobas compared to ARCHITECT was 0,94 (95 % CI= 0,84-1,04), and to ADVIA 0,63 (95 % CI=0,56-0,73), respectively, while slope for ARCHITECT compared to ADVIA was 0,75 (95 % CI=0,68-0,81). There was systematic difference between all 3 compared immunoassays, as well as proportional difference, except while comparing ARCHITECT against Cobas where proportional difference was not present.

Conclusion: We observed intermethod variability in all compared 25(OH)D assays, especially while comparing some of single samples against each other, where remarkable differences were present. In routine clinical laboratory all three immunoassays and LC-MS/MS are useful for measuring 25(OH)D. However, it is important for clinicians to be informed that these intermethod differences can have direct impact on interpretation of the results and patients should be followed up in the same laboratory.  

Keywords: Method