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Letter to the Editor |
Boston University Medical Center School of Medicine Boston, Massachusetts 02118
Address correspondence to: Dr. Michael F. Holick,1 M.D., Ph.D., Boston University Medical Center, School of Medicine, 715 Albany Street, M 1013, Boston, Massachusetts 02118.
To the editor:
Recently, Binkley et al. (1), with results from seven laboratories using either RIA, HPLC, or an automated chemiluminescence assay, reported that the degree of variability of the results between methods and between laboratories, even when using the same method, confounded diagnosis of vitamin D insufficiency. The authors should be complimented for bringing this methodological variability to clinicians’ attention. An editorial by Hollis (2) reviews the evolution of the 25-hydroxyvitamin D [25(OH)D] assay development using either the vitamin D binding protein (DBP) or an antibody to 25(OH)D (RIA). He notes that all of the laboratories that performed the Nichols Advantage assay showed significant overestimation of basal concentrations of circulating 25(OH)D. However, he reports on phone call accounts of clinicians stating that patients receiving vitamin D2 showed no increase in 25(OH)D levels. He also mentions results from a UK-based survey group (DEQAS) with one patient with vitamin D deficiency who was treated with vitamin D2 and who did not show any increase in 25(OH)D using the Nichols Advantage assay. Based on this one observation, Hollis condemns both the Advantage CPBA system and the IDS/RIA systems. He further states that using these assays could lead to misdiagnosis and subsequent dangerous consequences for patients, such as hypervitaminosis D. The technical brief from DEQAS is now published, and it clearly indicates that the Nichols Advantage assay does detect 25(OH)D2, although values are lower for the samples they tested (3).
The statements in the editorial by Hollis (2) were surprising, and the conclusions seemed unwarranted based on the Binkley et al. data about which the editorial was written. I have been an academic associate for Nichols Institute for 25 yr. I helped them develop the first commercial assay for 25(OH)D. The DBP was used as the binder for the assay because it recognizes 25(OH)D2 and 25(OH)D3 equally well. The suggestion that the Advantage assay does not recognize 25(OH)D2 based on limited information from patients on whom we have little information is highly irregular. Recently, Gemar et al. (4) reported that in seven patients who received 150,000 IU of vitamin D2 and were followed for 7 d, the blood level of 25(OH)D was similar at d 7 using the Advantage assay compared with HPLC, the gold standard assay. This was also confirmed by my laboratory. We reported on 19 patients who had received pharmacological 50,000-IU doses of vitamin D2 (5). We observed that all of the patients showed increases above baseline in their 25(OH)D levels. All patients did underestimate total 25(OH)D compared with liquid chromatography/mass spectrometry by about 60%.
I agree with both Binkley et al. (1) and Hollis (2) that rigorous oversight is needed to make certain that the 25(OH)D assay that is available to clinicians is accurate not only in detecting vitamin D inadequacy but also in correcting vitamin D inadequacy after pharmacological treatment with vitamin D2. Additional research is needed to better understand why Nichols Advantage assay underestimates 25(OH)D in some patients and why the Diasorin and Advantage assay has been reported to overestimate total 25(OH)D levels.
Footnotes
1 Dr. Holick is a consultant for the Nichols Institute. 
A response to this letter was invited, but the authors of the original article chose not to provide one.
Received January 25, 2005.
References
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