Abstract

BORDALLO, C.F.  and  SAAVEDRA, M.S.. Controversies in measuring 25 (OH) Vitamin D: comparison of two methodologies. Rev. argent. endocrinol. metab. [online]. 2011, vol.48, n.2, pp.69-77. ISSN 1851-3034.

Introduction: The methods used for vitamin D measurement have several methodological aspects still not defined, such as reference method, traceability of international standard, specificity, etc, which generates great discrepancies between the results obtained. Objective: To compare the results of vitamin D measurements obtained with two different immunoassays of different specificity and standardization, and their impact on clinical interpretation in patients treated and not treated with vitamin D₂ or D₃. Materials and Methods: Two groups are considered for comparison of the methods: G1 (95 serum samples from patients who were receiving vitamin D₂, vitamin D₃ or no medication) and G2 (40 serum samples after excluding the 55 patients who received vitamin D₂). Results: There are great differences between the samples measured by both assays. We found highly significant differences between means in G1 (p <0.0001) and significant differences in G2 (p < 0.0038). No correlation was observed between EQLIA vs. RIA in the G1 (r = -0.00671, p = 0.9483) but good correlation in G2. (r = 0.898, p < 0.0000). Although ECLIA was in agreement with RIA, in G1 the results of the methods shows a wide dispersion around the mean of the difference 20.8 ng / ml. In contrast, in G2 there is a better match between results (mean of the difference 6.4 ng/ml). Conclusions: This comparison of methods allowed us to identify two critical situations to consider when measuring vitamin D: first, whether the patient has been supplemented or not with Vitamin D, and in that case, if he/she has been given D₂ or D₃, and secondly, the method used for measurement. Discrepancies between the results of vitamin D measurements obtained by different methodologies will impact on the clinical usefulness of the report issued by the laboratory, and consequently in the interpretation and medical decision.

Keywords : 25 (OH)vitamina D3; Vitamin D; Measurement of vitamin D.

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