Proposal of a candidate international conventional reference measurement procedure for free thyroxine in serum

2007 ◽  
Vol 45 (7) ◽  
Author(s):  
International Federation of Clinica Thienpont ◽  
Graham Beastall ◽  
Nicholas D. Christofides ◽  
James D. Faix ◽  
Tamio Ieiri ◽  
...  
Keyword(s):  
Equilibrium Dialysis ◽  
Metrological Traceability ◽  
Measurement Procedure ◽  
Free Thyroxine ◽  
Tandem Ms ◽  
Reference Measurement ◽  
Reference Measurement Procedure ◽  
Liquid Chromatography Tandem Mass ◽  
Total Thyroxine ◽  
Lc Tandem Ms

AbstractIn the present paper the IFCC WG-STFT recommends and provides the rationale to establish metrological traceability of serum free thyroxine (FT4) measurements to a candidate international conventional reference measurement procedure. It is proposed that this procedure be based on equilibrium dialysis combined with determination of thyroxine in the dialysate with a trueness-based reference measurement procedure. The measurand is thus operationally defined as “thyroxine in the dialysate from equilibrium dialysis of serum prepared under defined conditions”. With regard to the trueness-based reference measurement procedure, the WG-STFT recommends use of an isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC/tandem MS) procedure for total thyroxine that has been optimized towards measurement at picomolar concentration levels and that is listed in the database of the Joint Committee for Traceability in Laboratory Medicine (JCTLM). For calibration, the purified thyroxine material IRMM-468 (resulting from a project funded by the European Commission and recently submitted to the JCTLM) is proposed. The WG-STFT stresses that according to this recommendation it is a prerequisite to strictly adhere to the defined equilibrium dialysis procedure, whereas it is permissible to introduce variants in the ID-LC/tandem MS procedure.Clin Chem Lab Med 2007;45:934–6.

scholarly journals Feasibility of Standardization of Serum C-Peptide Immunoassays with Isotope-Dilution Liquid Chromatography–Tandem Mass Spectrometry

2006 ◽  
Vol 52 (6) ◽  
pp. 1193-1196 ◽  
Author(s):  
Diego Rodríguez Cabaleiro ◽  
Dietmar Stöckl ◽  
Jean M Kaufman ◽  
Tom Fiers ◽  
Linda M Thienpont
Keyword(s):  
Mass Spectrometry ◽  
Liquid Chromatography ◽  
Isotope Dilution ◽  
Method Comparison ◽  
Measurement Procedure ◽  
Tandem Ms ◽  
C Peptide ◽  
Reference Measurement ◽  
Reference Measurement Procedure ◽  
Lc Tandem Ms

Abstract Background: Serum C-peptide concentrations reflect pancreatic function in different clinical and diagnostic settings; however, the utility of C-peptide testing is limited by the lack of standardized commercial immunoassays. Standardization can best be done by split-sample comparison with a hierarchically higher reference measurement procedure with a set of native sera. For serum peptides, isotope-dilution liquid chromatography–mass spectrometry (ID-LC/MS) is recommended as a reference measurement procedure. Methods: We evaluated the analytical performance characteristics of an ID-LC/tandem MS procedure for measurement of serum C-peptide after a 2-step solid-phase extraction. To investigate the feasibility of this procedure for use in standardization, we also performed a method comparison with 3 representative commercial assays. Results: The ID-LC/tandem MS procedure showed maximum within-run, between-run, and total CVs on dedicated sera (C-peptide concentrations, 1.6 and 4.0 μg/L) of 2.1%, 2.5%, and 2.9%, respectively; an accuracy of 94.6%–104.1%; a minimum trueness of 98.1% (95% confidence interval, 96.2%–100.0%), and limits of quantification and detection of 0.15 and 0.03 μg/L, respectively. Deming linear regression analysis of the method-comparison data showed that the immunoassays correlated well with ID-MS and were specific, but lacked intercomparability and trueness. We propose that the deficiencies can be resolved by recalibration on the basis of the method comparison. Conclusions: The ID-LC/tandem MS procedure is suitable for specific and accurate measurement of basal and stimulated serum concentrations of proinsulin C-peptide fragment 33–63 and is suitable for use in standardization of C-peptide immunoassays.

IFCC international conventional reference procedure for the measurement of free thyroxine in serum

2011 ◽  
Vol 49 (8) ◽  
Author(s):  
Sofie K. Van Houcke ◽  
Katleen Van Uytfanghe ◽  
Eri Shimizu ◽  
Wataru Tani ◽  
Masao Umemoto ◽  
...  
Keyword(s):  
Equilibrium Dialysis ◽  
Free Thyroxine ◽  
Regenerated Cellulose ◽  
Tandem Ms ◽  
Thyroid Function Tests ◽  
Thermostatic Control ◽  
Reference Procedure ◽  
Amount Of Substance ◽  
Calibration Measurement ◽  
Lc Tandem Ms

AbstractThe IFCC Working Group for Standardization of Thyroid Function Tests proposes a candidate international conventional reference procedure (RMP) for measurement of the amount-of-substance concentration of free thyroxine in plasma/serum at physiological pH 7.40 and temperature (37.0°C). The unit for reporting measurement results is, by convention, pmol/L. The RMP is based on equilibrium dialysis isotope dilution-liquid chromatography/tandem mass spectrometry (ED-ID-LC/tandem MS). The rationale for proposing a conventional RMP is that, because of the physical separation step, it is unknown whether the measurement truly reflects the concentration of free thyroxine (FT4) in serum. Therefore, the ED part of the RMP has to strictly adhere to the following conditions: use of a dialysis buffer with a biochemical composition resembling the ionic environment of serum/plasma as closely as possible; buffering of the sample to a pH of 7.40 (at 37.0°C) before dialysis, however, without additional dilution; dialysis in a device with a dialysand/dialysate compartment of identical volume and separated by a membrane of regenerated cellulose and adequate cut-off; thermostatic control of the temperature during dialysis at 37.0°C±0.50°C. The convention does not apply to the ID-LC/tandem MS part, provided it is eligible to be nominated for review by the Joint Committee for Traceability in Laboratory Medicine. Here, we describe the ED procedure, inclusive its validation and transferability, in greater detail. We recommend a protocol for successful calibration, measurement and monitoring of the accuracy/trueness and precision of the candidate conventional RMP. For details on our ID-LC/tandem MS procedures, we refer to the Supplement.

scholarly journals Standardization of Free Thyroxine Measurements Allows the Adoption of a More Uniform Reference Interval

2017 ◽  
Vol 63 (10) ◽  
pp. 1642-1652 ◽  
Author(s):  
Linde A C De Grande ◽  
Katleen Van Uytfanghe ◽  
Dries Reynders ◽  
Barnali Das ◽  
James D Faix ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Equilibrium Dialysis ◽  
Total Error ◽  
Reference Interval ◽  
Measurement Procedure ◽  
Free Thyroxine ◽  
Thyroid Function Tests ◽  
Proof Of Concept ◽  
Reference Measurement ◽  
Statistical Procedures

Abstract BACKGROUND The IFCC Committee for Standardization of Thyroid Function Tests intended to standardize free thyroxine (FT4) immunoassays. We developed a Système International d'Unités traceable conventional reference measurement procedure (RMP) based on equilibrium dialysis and mass spectrometry. We describe here the latest studies intended to recalibrate against the RMP and supply a proof of concept, which should allow continued standardization efforts. METHODS We used the RMP to target the standardization and reference interval (RI) panels, which were also measured by 13 manufacturers. We validated the suitability of the recalibrated results to meet specifications for bias (3.3%) and total error (8.0%) determined from biological variation. However, because these specifications were stringent, we expanded them to 10% and 13%, respectively. The results for the RI panel were reported as if the assays were recalibrated. We estimated all but 1 RI using parametric statistical procedures and hypothesized that the RI determined by the RMP was suitable for use by the recalibrated assays. RESULTS Twelve of 13 recalibrated assays had a bias, meeting the 10% specification with 95% confidence; for 7 assays, this applied even for the 3.3% specification. Only 1 assay met the 13% total error specification. Recalibration reduced the CV of the assay means for the standardization panel from 13% to 5%. The proof-of-concept study confirmed our hypothesis regarding the RI but within constraints. CONCLUSIONS Recalibration to the RMP significantly reduced the FT4 immunoassays' bias, so that the RI determined by the RMP was suitable for common use within a margin of 12.5%.

scholarly journals Thrombin: An Approach to Developing a Higher-Order Reference Material and Reference Measurement Procedure for Substance Identity, Amount, and Biological Activities

2020 ◽  
Vol 125 ◽  
Author(s):  
Craig M. Jackson ◽  
M. Peter Esnouf ◽  
David L. Duewer
Keyword(s):  
Reference Material ◽  
Reference Materials ◽  
Biological Activities ◽  
Metrological Traceability ◽  
Catalytic Efficiency ◽  
Measurement Procedure ◽  
Protein Characterization ◽  
Reference Measurement ◽  
Reference Measurement Procedure ◽  
Hydrolytic Activities

Thrombin, the proteolytic enzyme that catalyzes the transformation of soluble fibrinogen to the polymerized fibrin clot, participates in multiple reactions in blood coagulation in addition to the clotting reaction. Although reference materials have existed for many years, structural characterization and measurement of biological activity have never been sufficient to permit claims of clear metrological traceability for the thrombin preparations. Our current state-of-the-art methods for protein characterization and determination of the catalytic properties of thrombin now make it practical to develop and characterize a metrologically acceptable reference material and reference measurement procedure for thrombin. Specifically, α-thrombin, the biologically produced protease formed during prothrombin activation, is readily available and has been extensively characterized. Dependences of thrombin proteolytic and peptide hydrolytic activities on a variety of substrates, pH, specific ions, and temperature are established, although variability remains for the kinetic parameters that describe thrombin enzymatic action. The roles of specific areas on the surface of the thrombin molecule (exosites) in substrate recognition and catalytic efficiency are described and characterized. It is opportune to develop reference materials of high metrological order and technical feasibility. In this article, we review the properties of α-thrombin important for its preparation and suggest an approach suitable for producing a reference material and a reference measurement procedure that is sensitive to thrombin’s catalytic competency on a variety of substrates.

scholarly journals Reference Measurement Procedure for Total Glycerides by Isotope Dilution GC-MS

2012 ◽  
Vol 58 (4) ◽  
pp. 768-776 ◽  
Author(s):  
Selvin H Edwards ◽  
Shelton L Stribling ◽  
Susan D Pyatt ◽  
Mary M Kimberly
Keyword(s):  
Isotope Dilution ◽  
Limit Of Detection ◽  
Metrological Traceability ◽  
Measurement Procedure ◽  
Chromotropic Acid ◽  
Serum Samples ◽  
Buffer Solution ◽  
Reference Measurement ◽  
Reference Measurement Procedure ◽  
The Mean

Abstract BACKGROUND The CDC's Lipid Standardization Program established the chromotropic acid (CA) reference measurement procedure (RMP) as the accuracy base for standardization and metrological traceability for triglyceride testing. The CA RMP has several disadvantages, including lack of ruggedness. It uses obsolete instrumentation and hazardous reagents. To overcome these problems the CDC developed an isotope dilution GC-MS (ID-GC-MS) RMP for total glycerides in serum. METHODS We diluted serum samples with Tris-HCl buffer solution and spiked 200-μL aliquots with [13C3]-glycerol. These samples were incubated and hydrolyzed under basic conditions. The samples were dried, derivatized with acetic anhydride and pyridine, extracted with ethyl acetate, and analyzed by ID-GC-MS. Linearity, imprecision, and accuracy were evaluated by analyzing calibrator solutions, 10 serum pools, and a standard reference material (SRM 1951b). RESULTS The calibration response was linear for the range of calibrator concentrations examined (0–1.24 mmol/L) with a slope and intercept of 0.717 (95% CI, 0.7123–0.7225) and 0.3122 (95% CI, 0.3096–0.3140), respectively. The limit of detection was 14.8 μmol/L. The mean %CV for the sample set (serum pools and SRM) was 1.2%. The mean %bias from NIST isotope dilution MS values for SRM 1951b was 0.7%. CONCLUSIONS This ID-GC-MS RMP has the specificity and ruggedness to accurately quantify total glycerides in the serum pools used in the CDC's Lipid Standardization Program and demonstrates sufficiently acceptable agreement with the NIST primary RMP for total glyceride measurement.

scholarly journals Proposed Serum Cholesterol Reference Measurement Procedure by Gas Chromatography–Isotope Dilution Mass Spectrometry

2011 ◽  
Vol 57 (4) ◽  
pp. 614-622 ◽  
Author(s):  
Selvin H Edwards ◽  
Mary M Kimberly ◽  
Susan D Pyatt ◽  
Shelton L Stribling ◽  
Kara D Dobbin ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Serum Cholesterol ◽  
Isotope Dilution ◽  
Isotope Dilution Mass Spectrometry ◽  
Measurement Procedure ◽  
Standard Reference Materials ◽  
Reference Measurement ◽  
Reference Measurement Procedure ◽  
The Mean

BACKGROUND Our purpose was to establish a mass spectrometry reference measurement procedure (RMP) for cholesterol to use in the CDC's standardization programs. We explored a gas chromatography–isotope dilution mass spectrometry (GC-IDMS) procedure using a multilevel standard calibration curve to quantify samples with varying cholesterol concentrations. METHODS We calibrated the mass spectrometry instrument by isotope dilution with a pure primary standard reference material and an isotopically enriched cholesterol analog as the internal standard (IS). We diluted the serum samples with Tris-HCl buffer (pH 7.4, 0.05 mol/L, 0.25% Triton X-100) before analysis. We used 17 serum pools, 10 native samples, and 2 standard reference materials (SRMs). We compared the GC-IDMS measurements with the CDC's modified Abell–Levy–Brodie–Kendall (AK) RMP measurements and assessed method accuracy by analyzing 2 SRMs. We evaluated the procedure for lack of interference by analyzing serum spiked with a mixture of 7 sterols. RESULTS The mean percent bias between the AK and the GC-IDMS RMP was 1.6% for all samples examined. The mean percent bias from NIST's RMP was 0.5% for the SRMs. The total %CVs for SRM 1951b levels I and II were 0.61 and 0.73%, respectively. We found that none of the sterols investigated interfered with the cholesterol measurement. CONCLUSIONS The low imprecision, linear response, lack of interferences, and acceptable bias vs the NIST primary RMP qualifies this procedure as an RMP for determining serum cholesterol. The CDC will adopt and implement this GC-IDMS procedure for cholesterol standardization.

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