Importance of the isolation of hydroxyvitamin D before assay. This suggests that the problem is not confined to DEQAS samples, an explanation originally proposed by the manufacturer to explain the overrecovery of 25OHD 3. Method means of samples known to contain 25OHD 2 were excluded. In summary, an international quality assessment scheme has demonstrated that, for samples containing only 25OHD 3 , most commercial 25OHD methods are capable of giving results close to the target value, but the results are highly operator dependent. Vitamin-D-deficient neonates failed to show an increase in 25OHD, despite receiving large doses of ergocalciferol. The results are presented in Fig.

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Low recovery of 25OHD 2 by the Nichols automated assay has also been observed in clinical samples Dr. The results are presented in Fig. Method means deqas-t samples known to contain 25OHD 2 were excluded.

In brief, five samples of normal human sera are dfqas-r out at 3-month intervals. Assay variation confounds the diagnosis of hypovitaminosis D: Outliers in clinical chemistry quality-control schemes. The one automated procedure Nichols produced more consistent values, but for the samples 1, 2, and 3 containing only 25OHD 3the results were again higher than those of other methods.

Early attempts to simplify competitive protein binding assays for 25OHD, by abandoning the preliminary chromatographic step, failed because interfering substances in the sample matrix led to deqas- results 9 Measurement of vitamin D metabolites: The positive intercept 8.

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View inline View popup. Since this article was submitted, Nichols Institute Diagnostics has issued a technical note in which they acknowledge that some samples containing substantial quantities of 25OHD 2 give low results in the Advantage automated assay.

deqas-r

J Lab Clin Med ; The possibility that sodium azide, formerly used as a preservative in DEQAS samples, could have interfered in the chemiluminescence endpoint of the Nichols assay was considered but discounted because the bias persisted after the use of azide was abandoned in In essence, DEQAS is an ongoing, multicenter trial of the methods used by its participants and provides a unique opportunity to assess the accuracy and specificity of 25OHD methods as well as the analytical performance of a large number of their users.

The overall accuracy of each method can be assessed from the percentage bias of the method mean from the ALTM: Concerns have also been raised about the apparent inability of some 25OHD assays to reliably measure hydroxyvitamin D 2 25OHD ceqas-r 2 3 4.

deqas-r

The Nichols automated assay gives more consistent results but generally produces higher values than other methods. Table of Contents Index by author. Vitamin D; chemistry, biology and clinical applications of the steroid hormone Comparison of commercially available I-based methods for the determination of circulating drqas-r D.

Hydroxyvitamin D assays: An historical perspective from DEQAS.

The treatment of vitamin-D-deficient patients could be severely compromised by the use of assays that underestimate 25OHD 2. A rapid assay for OH-vitamin D 3 without preparative chromatography. This suggests that the problem is not confined to DEQAS samples, an explanation originally proposed by the manufacturer to ceqas-r the overrecovery of 25OHD 3. Skip to main content. Vitamin-D-deficient neonates failed to show an increase in 25OHD, despite receiving large doses of ergocalciferol.

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Hydroxyvitamin D assays: An historical perspective from DEQAS.

Samples known to contain 25OHD 2 were excluded. Linear regression analysis was performed to define the relationship between method means and the ALTM x ; the results were as follows correlation coefficients in parentheses: A recent report highlighted the interlaboratory variability in serum hydroxyvitamin D 25OHD results 1. Vitamin D endocrine system; structural, biological, genetic and clinical aspects Among the five samples distributed in January were two samples 4 and 5 containing endogenous 25OHD 2.

The accurate measurement of this metabolite is essential for the monitoring of vitamin-D-deficient patients receiving ergocalciferol, which is the only supplement used in the United States 5 and widely used elsewhere. Show more Technical Briefs.

deqas-r

The validity of 25OHD results will, justifiably, continue to be questioned. In summary, an international quality assessment scheme has demonstrated that, for samples containing only 25OHD 3most commercial 25OHD methods are capable of giving reqas-r close to the target value, but the results are highly operator dependent.