Serum Vitamin D Measurement May Not Reflect What You Give to Your Patients

Abstract

The recognized index of vitamin D (VTD) status is the measurement of circulating concentrations of 25-OH VTD (25VTD). A concentration of 30 ng/ml 25VTD (75 nM) is considered by many experts as the minimum optimal concentration.(1) There is currently a growing interest in VTD far beyond bone and calcium metabolism, (2) including cancer, immunology, and hypertension, which has caused a recent upsurge in requests for 25VTD evaluation, (3) necessitating the need for accurate measurement.We report here the case of a 60-yr-old woman diagnosed as having VTD deficiency (serum 25VTD measured with the automated Roche Elecsys method at 12 ng/ml). She was given a single 600,000U VTD 2 oral dose. Because serum 25VTD measured with the same assay 2 wk later was still low (11 ng/ml), she was referred to our unit for extensive laboratory testing. All biochemical parameters were normal, including 25VTD (50 ng/ml), but this time the Diasorin radioimmunoassay (RIA) was used to quantify 25VTD. To study the cause for these discrepant results further, we conducted measurements of 25VTD by a specific liquid chromatography-mass spectrometry (LC/MS/MS) method. The LC/MS/MS method separates and quantifies 25-hydroxylated metabolites of both VTD 2 and VTD 3 , which are summed to get the total 25VTD concentration. The LC/MS/MS is considered by many as the candidate reference method for 25(OH)D measurement, (4) although drawbacks because of the recognition of other compounds such as epimers have been highlighted, especially in pediatric subjects. (5,6) In addition to the index case, all three methods were used to measure 25VTD in serum collected from 11 healthy subjects (5 men and 6 women; age, 21-62 yr) before (D0) and 7 and 28 days after a single 600,000U VTD 2 dose to mimic the above-mentioned case. Pooling the results from the three time-points, we found that the LC/MS/MS results were highly correlated with the RIA values (Spearman's ‫ס‬ 0.94; p < 0.0001) but not with the Elecsys values ( ‫ס‬ 0.16; not significant).On day 0, the mean concentration [SD] was similar with the three assays (Diasorin RIA: 29.3 [6.8] 4] ng/ ml) with the Roche Elecsys assay. All subjects had a 25VTD concentration >30 ng/ml with LC/MS/MS and the Diasorin RIA, whereas this was the case in only two of them with the Elecsys. At day 28, 25VTD remained >30 ng/ml in all subjects when measurements were conducted by Diasorin RIA (52.0 [20.3] ng/ml) and LC/MS/MS (52.8 [8.5] ng/ml), whereas it was <30 ng/ml (21.4 [4.9] ng/ml) in all subjects with the Elecsys assay (Fig. 1). The LC/MS/MS data confirmed that the increases observed were solely caused by an increase in the 25VTD 2 metabolite.The supplementation with 600,000 IU of VTD 2 did not produce a significant rise in calcium and phosphorus levels (2.35, 2.35, and 2.39 mM, respectively, for day 0, 7, and 28 median calcium levels and 1.07, 1.05, and 1.06 mM, respectively, for phosphorus concentrations at the same times). We did not observe any significant variation in parathormone levels (41 versus 44 pg/ml before and a...

Vitamin D: current status and perspectives

“…Indeed, although skin exposure to UVB produces vitamin D3 and food sources of vitamin D contain mainly vitamin D3, supplementation is often made with vitamin D2, especially in the USA. As long as vitamin D2 is available, it is mandatory to measure 25VTD with a method that recognizes both 25VTD2 and 25VTD3 in order to avoid underestimation of the vitamin D status and thus potentially lead to overtreatment, and to expensive and stressful explorations (21).…”

Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D

“…(6) We have found that administration relative to meal intake can be an additional factor that results in unpredictable serum 25(OH)D levels even when a proper assay is used. We commonly find that patients take the medication on an empty stomach or with a light meal.…”

Analytical methods and performance of the immunoassay methods for determination of vitamin d in comparison to mass spectrometry / Analitičke metode i izvođenje imunometrijskih određivanja vitamina d u poređenju sa masenom spektrometrijom

“…Nonetheless, unless the laboratorians recognize limitations of their assay, significant confusion can arise. This was nicely illustrated in the case report from Belgium where physicians treated vitamin D deficient patient with vitamin D 2 , while her serum vitamin D levels were measured using the vitamin D 3 assay (34). It is also important to recognize that none of the studies published on comparison of automated immunoassays with LC-MS/MS methodology recruited more than a few patients supplemented with vitamin D 2 .…”