Comparison of four routinely used vitamin D automated immunoassays.

Jindra Windrichova,Radka Fuchsova,Ladislav Pecen,Radek Kucera,Ondrej Topolcan,Pavel Broz,Otto Mayer

doi:10.5937/jomb0-27531

Abstract

BackgroundTo compare four automated immunoassays for the measurement of 25(OH)-vitamin D (25-OHD) and to assess the impact on the results obtained from a healthy population.MethodsWe analysed 100 serum samples on Unicel DxI 800 (Beckman Coulter), Architect i1000 (Abbott), Cobas e411 (Roche) and Liaison XL (DiaSorin). Passing-Bablok regression and Bland-Altman plots were used for method comparison. In order to categorise the obtained values, results were categorised into the following groups: 0-25 nmol/L, 25-50 nmol/L, 50-75 nmol/L and above 75 nmol/L and compared. The percentage of samples below 75 nmol/L, and below 50 nmol/L was then calculated for every method.ResultsAccording to paired comparisons, each method differs from others (p<0.0001) except Cobas vs Architect, which do not show a statistically significant difference (p=0.39). The strongest correlation was found between Liaison and Architect (ρ=0.94, p<0.0001). The percentage of samples below the recommended value of 75 nmol/L were: 70% (Architect), 92% (Liaison), 71% (Cobas) and 89% (Unicel). The percentage of samples below the value of 50 nmol/L were: 17% (Architect), 55% (Liaison), 28% (Cobas) and 47% (Unicel).ConclusionsThe observed differences stem from the use of different analytical systems for 25-OHD concentration analysis and can result in different outcomes. The recommended values should be established for each assay in accordance with the data provided by the manufacturer or in the laboratory, in accordance with proper standardisation.

Highlights

Vitamin D is involved in bone metabolism and in cardiovascular, neurological and autoimmune diseases, as well as tumorigenesis
The observed differences stem from the use of different analytical systems for 25(OH)-vitamin D (25-OHD) concentration analysis and can result in different outcomes
The best marker of vitamin D levels in the body is 25(OH)-vitamin D (25-OHD), present in the highest quantity in the blood. 25-OHD concentrations reflect both the endogenously synthesised and the exogenous form of vitamin D contained in food and supplementation [1]

Summary

Introduction

Vitamin D is involved in bone metabolism and in cardiovascular, neurological and autoimmune diseases, as well as tumorigenesis. Vitamin D concentrations are routinely measured in clinical practice and research. Difficulties in interpreting vitamin D values impair the effective use of vitamin D measurements in both routine practice and clinical research. The analytical difficulties encountered are related to its lipophilic nature, a strong affinity to vitamin D binding protein (VDBP), the existence of two molecular forms (D2 and D3) and the presence of interfering metabolites (e.g. 24,25-dihydroxy vitamin, C3-epimer of 25-OHD3). The first analytical method for measurement of 25-OHD concentration was described in the 1970s based on chromatography principles. In 1985, a radioimmunoassay measurement (RIA) was developed based on a specific antibody, becoming the first of its kind to be approved by the Food and Drug Administration (FDA) for clinical diagnostics of vitamin D deficiency. The progress in tandem mass spectrometry enabled the introduction of a routine LC MS/MS method in 2004 [4]

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