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Comparative Study
. 2010 Jul 13;5(7):e11555.
doi: 10.1371/journal.pone.0011555.

Determining vitamin D status: a comparison between commercially available assays

Greta Snellman  1 , Håkan Melhus, Rolf Gedeborg, Liisa Byberg, Lars Berglund, Lisa Wernroth, Karl Michaëlsson
Affiliations
Comparative Study

Determining vitamin D status: a comparison between commercially available assays

Greta Snellman et al. PLoS One. .

Erratum in

  • PLoS One. 2010;5(9). doi: 10.1371/annotation/23307aa4-726e-4f11-86c0-8a292be33517

Abstract

Background: Vitamin D is not only important for bone health but can also affect the development of several non-bone diseases. The definition of vitamin D insufficiency by serum levels of 25-hydroxyvitamin D depends on the clinical outcome but might also be a consequence of analytical methods used for the definition. Although numerous 25-hydroxyvitamin D assays are available, their comparability is uncertain. We therefore aim to investigate the precision, accuracy and clinical consequences of differences in performance between three common commercially available assays.

Methodology/principal findings: Serum 25-hydroxyvitamin D levels from 204 twins from the Swedish Twin Registry were determined with high-pressure liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS), a radioimmunoassay (RIA) and a chemiluminescent immunoassay (CLIA). High inter-assay disagreement was found. Mean 25-hydroxyvitamin D levels were highest for the HPLC-APCI-MS technique (85 nmol/L, 95% CI 81-89), intermediate for RIA (70 nmol/L, 95% CI 66-74) and lowest with CLIA (60 nmol/L, 95% CI 56-64). Using a 50-nmol/L cut-off, 8% of the subjects were insufficient using HPLC-APCI-MS, 22% with RIA and 43% by CLIA. Because of the heritable component of 25-hydroxyvitamin D status, the accuracy of each method could indirectly be assessed by comparison of within-twin pair correlations. The strongest correlation was found for HPLC-APCI-MS (r = 0.7), intermediate for RIA (r = 0.5) and lowest for CLIA (r = 0.4). Regression analyses between the methods revealed a non-uniform variance (p<0.0001) depending on level of 25-hydroxyvitamin D.

Conclusions/significance: There are substantial inter-assay differences in performance. The most valid method was HPLC-APCI-MS. Calibration between 25-hydroxyvitamin D assays is intricate.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Mean serum 25-hydroxyvitamin D by assay.
The error bars indicate 95% confidence intervals.
Figure 2
Figure 2. Seasonal differences in 25-hydroxyvitamin D levels for the HPLC-APCI-MS, RIA and CLIA assays.
The error bars indicate 95% confidence intervals.
Figure 3
Figure 3. Cumulative proportion of the subjects who are classified as insufficient using a 50 nmol/L cut-off.
HPLC-APCI-MS 8%, RIA 22%, CLIA 43%.
Figure 4
Figure 4. Bland Altman plots for the difference in 25-hydroxyvitamin D level between the assays.
HPLC-APCI-MS vs. RIA (panel A), HPLC-APCI-MS vs. CLIA (panel B) and RIA vs. CLIA (panel C). Each circle represents one twin.
See this image and copyright information in PMC

References

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