Serum 25-Hydroxyvitamin D Immunoassays: Recommendations for Correct Clinical Interpretation

We read with interest the report by Leino et al. (1) concerning the analytical evaluation of the 25-hydroxyvitamin D3 (25-OH-D3)1 assay on the Roche Modular analyzer. They used clinical samples that were almost free of 25-hydroxyvitamin D2 (25-OH-D2) (<10 nmol/L) as confirmed by liquid chromatography–tandem mass spectrometry (LC-MS/MS) and found a good overall agreement between the results obtained with the Roche assay and those measured with the DiaSorin RIA and by LC-MS/MS. Although they acknowledged that the Roche assay, which does not measure 25-OH-D2, may underestimate vitamin D status in patients receiving vitamin D2, they considered that underestimating was probably not a clinical problem in their country (Finland), because vitamin D supplementation in adults is most commonly provided as vitamin D3. We briefly discuss this point by reporting our own experience in France, where surveys performed in our units found that approximately 10%–15% of adult patients treated with vitamin D receive vitamin D …