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Hoofddorp, Netherlands

Heijboer A.C.,VU University Amsterdam | Blankenstein M.A.,VU University Amsterdam | Kema I.P.,University of Groningen | Buijs M.M.,Medial Diagnostic Centers
Clinical Chemistry | Year: 2012

BACKGROUND: Recent recognition of its broad pathophysiological importance has triggered an increased interest in 25-hydroxyvitamin D [25(OH)D]. By consequence, throughput in 25(OH)D testing has become an issue for clinical laboratories, and several automated assays for measurement of 25(OH)D are now available. The aim of this study was to test the accuracy and robustness of these assays by comparing their results to those of an isotope dilution/online solid-phase extraction liquid chromatography/tandem mass spectrometry (ID-XLC-MS/MS) method. We put specific focus on the influence of vitamin D-binding protein (DBP) by using samples with various concentrations of DBP. METHODS: We used 5 automated assays (Architect, Centaur, iSYS, Liaison, and Elecsys), 1 RIA (Diasorin) preceded by extraction, and an ID-XLC-MS/MS method to measure 25(OH)D concentrations in plasma samples of 51 healthy individuals, 52 pregnant women, 50 hemodialysis patients, and 50 intensive care patients. Using ELISA, we also measured DBP concentrations in these samples. RESULTS: Most of the examined 25(OH)D assays showed significant deviations in 25(OH)D concentrations from those of the ID-XLC-MS/MS method. As expected, DBP concentrations were higher in samples of pregnant women and lower in samples of IC patients compared to healthy controls. In 4 of the 5 fully automated 25(OH)D assays, we observed an inverse relationship between DBP concentrations and deviations from the ID-XLC-MS/MS results. CONCLUSIONS: 25(OH)D measurements performed with most immunoassays suffer from inaccuracies that are DBP concentration dependent. Therefore, when interpreting results of 25(OH)D measurements, careful consideration of the measurement method is necessary. © 2011 American Association for Clinical Chemistry.

Janssen M.J.W.,Viecuri Medical Center | Wielders J.P.M.,Meander Medical Center | Bekker C.C.,Viecuri Medical Center | Boesten L.S.M.,General Clinical Laboratory | And 5 more authors.
Steroids | Year: 2012

Objectives: Measurement of serum 25-hydroxyvitamin D [25(OH)D] is generally considered to be a reliable indicator of vitamin D status. The recent increase in diversity of 25(OH)D assays prompted us to evaluate the performance of chromatographic methods (two in-house ID-LC-MS/MS and HPLC (ClinRep, Recipe)), a protein binding method (Cobas-25(OH)D-total, Roche) and immunochemical methods (Liaison and RIA (Diasorin), iSYS (IDS), ADVIA Centaur (Siemens), and Architect i1000 and i2000 (Abbott)). Methods: Blood was drawn from randomly selected outpatients (N = 60) at one site after informed consent. DEQAS and SRM 972 samples were obtained from the scheme organizer and NIST, respectively. Serum aliquots were prepared, frozen and transported to participating centers. Method comparison was performed according to CLSI-EP9 specifications. Results: With these patient samples, and in comparison with ID-LC-MS/MS, Deming regression parameters slope, intercept and R were found to be within the ranges [0.57-1.07], [-1.7 to 6.9 nmol/L] and [0.88-0.98], respectively. 25(OH)D2 in DEQAS and SRM samples was fully recognized by chromatographic methods, but only partially by protein binding and immunochemical methods. Chromatographic methods, and to a lesser extent the protein binding assay, showed cross-reactivity with 3-epi-25(OH)D3. Agreement of 25(OH)D assays to ID-LC-MS/MS in sorting patients into distinct 25(OH)D categories varied between 53% and 88%. Conclusions: Significant bias exists between ID-LC-MS/MS and many, but not all, other 25(OH)D assays. The variable response among different assays for 25(OH)D metabolites impedes the use of uniform cut-off values for defining vitamin D status. Our results indicate the need towards further standardizing assays for 25(OH)D measurement. © 2012 Elsevier Inc. All rights reserved.

Buijs M.M.,Medial Diagnostic Centers | Gorgels J.P.M.C.,Medial Diagnostic Centers
Annals of Clinical Biochemistry | Year: 2011

There are many causes of interference in immunoassays causing erratic patient results. A method-specific interference due to antiruthenium antibodies in Roche free thyroxine (fT4) and free triiodothyronine (fT3) assays has been described previously. As a result, a new generation fT4 assay has been introduced by Roche. We describe six cases of interference due to antiruthenium antibodies, where in four cases interference in the Roche thyroid-stimulating hormone (TSH) assay was found as well. This raised the question as to whether other assays on this platform would also give incorrect results in patients with antiruthenium antibodies. Interference due to antiruthenium antibodies was suspected because of discrepancies between clinical presentation and/or TSH, fT4 and fT3 results. Samples of these six patients were reanalysed in Roche Diagnostics Laboratory, where it was demonstrated that the found discrepancies were indeed caused by interfering antiruthenium antibodies. Subsequently, these patients were asked to donate some blood once more for further evaluation, and three subjects agreed to participate. Their plasma was used to assay 18 analytes on Modular E and on a ruthenium-independent platform. The results were compared taking into account the known differences between distinct methods. As expected, significant interference was found in TSH. Also, in the new generation fT4 assay, ruthenium-induced interference was still present. However, the other assays, both competitive and immunometric, did not show clear interference. We therefore conclude that although antiruthenium antibodies theoretically can interfere in all assays on the Modular E platform, this kind of interference is found in the thyroid hormone assays, without marked interference in the other assays.

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