Standardisation and harmonisation of thyroid-stimulating hormone measurements: historical, current, and future perspectives.

Thyroid-stimulating hormone (TSH) is an important clinical marker in the diagnosis and management of thyroid disease. TSH measurements are reported in milli-International Units per Litre (mIU/L), traceable to a World Health Organisation (WHO) reference material. There is a wide variety of commercial immunoassays for TSH measurements available, which have historically been poorly harmonised due to a lack of commutability of the WHO reference materials with patient samples. This led to the recent development of a serum-based reference panel for TSH, traceable to the WHO reference material, available via the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC), aimed at harmonisation of TSH immunoassays. This report describes recent developments in the TSH reference system, including establishment of the 4th WHO International Standard for TSH, and aims to clarify the relationship between the available reference materials and their intended uses. This 4th WHO IS is widely available and defines the unit of TSH activity, therefore its continued existence is of paramount importance, however it continues to show a lack of commutability with patient in many TSH immunoassays. This makes the C-STFT TSH panel, albeit available in restricted numbers, a critical resource to ensure better TSH assay harmonisation.

Comparison and commutability study among four faecal immunochemical tests (FIT) systems.

OBJECTIVES: Faecal immunochemical tests for haemoglobin (FIT) are used in colorectal cancer screening programs around the world and increasingly for triage of symptomatic patients. FIT results are currently not traceable to a common reference standard and results obtained on various FIT systems may not be equivalent. The size of the bias between the systems is difficult to quantify due to the complex pre-analytical aspects of FIT. METHODS: This study aimed to quantify the bias and the correlation between four FIT systems by measuring a panel of 38 faecal samples while limiting the effect of the pre-analytical aspects. In addition, the commutability of seven candidate reference materials (RM) was assessed. RESULTS: Pairwise method comparisons based on faecal samples demonstrated Pearson correlation coefficients ranging between 0.944 and 0.970 and an average proportional bias of -30 to -35 % for one FIT system compared to the other three. The relative standard deviation among biases of the individual samples was around 20 %. Due to these sample specific differences, no decisive conclusions could be drawn in the commutability study. However, two candidate RMs, prepared in the FIT system-specific storage/extraction buffers, had a better commutable profile than the other five. CONCLUSIONS: The use of a common threshold for all FIT systems is currently not possible due to the presence of a proportional bias. We have identified potential commutable RMs to take to further studies on the production of a common calibrator, with the aim being to reduce the analytical bias observed on different FIT systems.

The role of analytical performance specifications in international guidelines and standards dealing with metrological traceability in laboratory medicine.

The goal of metrological traceability is to have equivalent results for a measurand in clinical samples (CSs) irrespective of the in-vitro diagnostic medical device (IVD-MD) used for measurements. The International Standards Organization standard 17511 defines requirements for establishing metrological traceability of values assigned to calibrators, trueness control materials and human samples used with IVD-MDs. Each step in metrological traceability has an uncertainty associated with the value assigned to a material. The uncertainty at each step adds to the uncertainty from preceding steps such that the combined uncertainty gets larger at each step. The combined uncertainty for a CS result must fulfil an analytical performance specification (APS) for the maximum allowable uncertainty (umax CS). The umax CS can be partitioned among the steps in a metrological traceability calibration hierarachy to derive the APS for maximum allowable uncertainty at each step. Similarly, the criterion for maximum acceptable noncommutability bias can be derived from the umax CS. One of the challenges in determining if umax CS is fulfilled is determining the repeatability uncertainty (u Rw) from operating an IVD-MD within a clinical laboratory. Most of the current recommendations for estimating u Rw from internal quality control data do not use a sufficiently representative time interval to capture all relevant sources of variability in measurement results. Consequently, underestimation of u Rw is common and may compromise assessment of how well current IVD-MDs and their supporting calibration hierarchies meet the needs of clinical care providers.

Aggregated data from the same laboratories participating in two glucose external quality assessment schemes show that commutability and transfers of values to control materials are decisive for the biases found.

OBJECTIVES: We report the results of glucose measurements performed during one year by the same measurement procedures (MPs) in 58 Norwegian hospital laboratories using control materials provided by external quality assessment (EQA) schemes from two different providers. The providers used materials with presumed vs. verified commutability and transfers of values using reference material vs. using a highest-order reference MP. METHODS: Data from six Labquality and three Noklus glucose EQA surveys were aggregated for each MP (Abbott Alinity, Abbott Architect, Roche Cobas, and Siemens Advia) in each scheme. For each EQA result, percent difference from target value (% bias) was calculated. Median percent bias for each MP per scheme was then calculated. RESULTS: The median % biases observed for each MP in the Labquality scheme were significantly larger than those in the Noklus scheme, which uses verified commutable control materials and highest-order reference MP target values. The difference ranged from 1.2 (Roche Cobas, 2.9 vs. 1.7 %) to 4.4 percentage points (Siemens Advia, 3.2 % vs. -1.2 %). The order of bias size for the various MPs was different in the two schemes. In contrast to the Labquality scheme, the median % biases observed in the Noklus scheme for Abbott Alinity (-0.1 %), Abbott Architect (-0.5 %), and Siemens Advia (-1.2 %) were not significantly different from target value (p>0.756). CONCLUSIONS: This study underlines the importance of using verified commutable EQA materials and target values traceable to reference MPs in EQA schemes designed for assessment of metrological traceability of laboratory results.

Commutability assessment of candidate reference materials for plasma renin activity measurement: current challenges.

OBJECTIVES: This study aims to evaluate the commutability of external quality assessment (EQA) materials and candidate reference materials (RMs) for plasma renin activity (PRA) assay. METHODS: Commutabilities of 16 candidate RMs were measured along with 40 clinical samples by the four different routine PRA assays, including three LC‒MS/MS assays and one chemiluminescence immunoassay. Sixteen candidate RMs included native/spiked human plasma pools (small-scale pools with <50 individuals) and current EQA materials (large-scale pools with >1,000 individuals). Difference in bias approach and linear regression with prediction interval approach were adopted to determine the commutability. Two-way variance analysis was used to estimate the effects of spiked and pool size on the commutability. Stability and homogeneity studies were performed. RESULTS: Precision and correlation performance of all assays was acceptable. In the difference in bias approach, the commutability results were not satisfactory (noncommutability: 14/16) and significant sample-specific effects were detected in assay pairs using different incubation buffers. For the prediction interval approach, no commutability was observed in the spiked small-scale pools; EQA materials (4/9) had more satisfactory commutability among all assays than the small-scale pools (2/7); RMs of large-scale pools tend to have better commutability no matter spiked or not. CONCLUSIONS: Commutable RMs were obtainable but challenging. Current EQA materials with relatively good commutability, stability, and homogeneity were appropriate RMs. Large-scale pools are tending to be commutable. Spiking in small-scale pools was not suggested to prepare RMs. MPs adopting a uniform incubation buffer would be preferable for further commutability research.

Assessing the commutability of candidate reference materials for the harmonization of neurofilament light measurements in blood.

OBJECTIVES: Neurofilament light chain (NfL) concentration in blood is a biomarker of neuro-axonal injury in the nervous system and there now exist several assays with high enough sensitivity to measure NfL in serum and plasma. There is a need for harmonization with the goal of creating a certified reference material (CRM) for NfL and an early step in such an effort is to determine the best matrix for the CRM. This is done in a commutability study and here the results of the first one for NfL in blood is presented. METHODS: Forty paired individual serum and plasma samples were analyzed for NfL on four different analytical platforms. Neat and differently spiked serum and plasma were evaluated for their suitability as a CRM using the difference in bias approach. RESULTS: The correlation between the different platforms with regards to measured NfL concentrations were very high (Spearman's ρ≥0.96). Samples spiked with cerebrospinal fluid (CSF) showed higher commutability compared to samples spiked with recombinant human NfL protein and serum seems to be a better choice than plasma as the matrix for a CRM. CONCLUSIONS: The results from this first commutability study on NfL in serum/plasma showed that it is feasible to create a CRM for NfL in blood and that spiking should be done using CSF rather than with recombinant human NfL protein.

Assessment of WHO 07/202 reference material and human serum pools for commutability and for the potential to reduce variability among soluble transferrin receptor assays.

OBJECTIVES: The clinical use of soluble transferrin receptor (sTfR) as an iron status indicator is hindered by a lack of assay standardization and common reference ranges and decision thresholds. In 2009, the WHO and National Institute for Biological Standards and Controls (NIBSC) released a sTfR reference material (RM), 07/202, for assay standardization; however, a comprehensive, formal commutability study was not conducted. METHODS: This study evaluated the commutability of WHO 07/202 sTfR RM and human serum pools and the impacts of their use as common calibrators. Commutability was assessed for six different measurement procedures (MPs). Serum pools were prepared according to updated CLSI C37-A procedures (C37) or non-C37 procedures. The study design and analyses were based on Parts 2 and 3 of the 2018 IFCC Commutability in Metrological Traceability Working Group's Recommendations for Commutability Assessment. WHO 07/202 and serum pools were used for instrument/assay and mathematical recalibration, respectively, to determine if their use decreases inter-assay measurement variability for clinical samples. RESULTS: The WHO 07/202 RM dilutions were commutable for all 6 MPs assessed and, when used for instrument calibration, decreased inter-assay variability from 208 to 55.7 %. Non-C37 and C37 serum pools were commutable for all 6 MPs assessed and decreased inter-assay variability from 208 to 13.8 % and 4.6 %, respectively, when used for mathematical recalibration. CONCLUSIONS: All materials evaluated, when used as common calibrators, substantially decreased inter-assay sTfR measurement variability. MP calibration to non-C37 and C37 serum pools may reduce the sTfR IMPBR to a greater extent than WHO 07/202 RM.

Exploration of suitable external quality assessment materials for serum C-peptide measurement.

OBJECTIVES: To find suitable external quality assessment (EQA) materials for serum C-peptide, we evaluated the commutability of five types of processed materials. METHODS: Seventy-four individual serum samples and 12 processed samples including three EQA samples currently in use, frozen human serum pools (FHSP), and three other kinds of processed samples were prepared by dissolving WHO International Standard Reagent for C-peptide (WHO ISR 13/146) in three different matrixes: 0.05 % bovine serum albumin, fetal bovine serum and human serum pools. Samples were analyzed using the isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method and six widely used immunoassays. The commutabilities of processed materials were assessed according to the difference in bias approach recommended by the IFCC. And the short- and long-term stability of FHSP samples at different temperatures were also evaluated. RESULTS: Out of the five kinds of processed materials, FHSP samples were commutable on most assays. In contrast, the EQA materials currently in use were only commutable on a few immunoassays. Additionally, processed materials derived from WHO ISR 13/146 were found to be un-commutable on over half of immunoassays. The FHSP samples could be stably stored at 4 and -20 °C for at least 16 days, and at -80 °C for at least 1 year, but at room temperature only for 12 h. CONCLUSIONS: With clarified commutability and stability information, the human serum pool samples along with the developed ID-LC-MS/MS method could be used in the EQA program to promote the comparability among laboratories for C-peptide measurement in China.

Commutability assessment of human urine certified reference materials for albumin and creatinine on multiple clinical analyzers using different statistical models.

Urine albumin concentration and albumin-creatinine ratio are important for the screening of early-stage kidney damage. Commutable urine certified reference materials (CRMs) for albumin and creatinine are necessary for standardization of urine albumin and accurate measurement of albumin-urine ratio. Two urine CRMs for albumin and creatinine with certified values determined using higher-order reference measurement procedures were evaluated for their commutability on five brands/models of clinical analyzers where different reagent kits were used, including Roche Cobas c702, Roche Cobas c311, Siemens Atellica CH, Beckman Coulter AU5800, and Abbott Architect c16000. The commutability study was conducted by measuring at least 26 authentic patient urine samples and the human urine CRMs using both reference measurement procedures and the routine methods. Both the linear regression model suggested by the Clinical and Laboratory Standard Institute (CLSI) guidelines and log-transformed model recommended by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Commutability Working Group were used to evaluate the commutability of the human urine CRMs. The commutability of the human urine CRMs was found to be generally satisfactory on all five clinical analyzers for both albumin and creatinine, suggesting that they are suitable to be used routinely by clinical laboratories as quality control or for method validation of urine albumin and creatinine measurements.

Accurate method for value assignment of carcinoembryonic antigen reference materials.

BACKGROUND: In this study, we explored the commutability of reference materials (RMs) for carcinoembryonic antigen (CEA), selected the appropriate diluent matrix of the first International Reference Preparation (IRP) 73/601 of the World Health Organization (WHO 73/601) for CEA, and improved the comparability of CEA measurement results among different assay systems. METHODS: Forty serum samples were divided into five aliquots. WHO 73/601 was diluted into nine concentrations using five diluents with different components, and the candidate RMs for CEA at five concentrations (C1-C5) were prepared by the Beijing Clinical Laboratory Center (BCCL). The samples were analyzed via five automated CEA immunoassays. RESULTS: Carcinoembryonic antigen candidate RMs were commutable among all immunoassays based on the CLSI approach and among 7 of 10 assay combinations based on the IFCC approach. WHO 73/601 diluted in phosphate-buffered saline (PBS) was commutable among all assays based on the CLSI approach and among 5 of 10 pairwise comparisons based on the IFCC approach with correction of bias at diluted concentrations, except for the lowest concentration, which had the smallest variation among systems. The median percentage biases among assays were decreased after calibration. CONCLUSION: The BCCL candidate RMs (C2-C5) for CEA were commutable among all immunoassays. WHO 73/601 RMs diluted in a PBS buffer matrix were selected as common calibrators for five immunoassays, which reduced bias, thereby effectively improving the harmonization of CEA detection; therefore, they could be used to assign values to CEA candidate RMs developed by BCCL. Our findings promote the harmonization of CEA detection in immunoassays.

Commutability evaluation of candidate reference materials and ERM-DA470k/IFCC for immunoglobulin M using two international approaches.

BACKGROUND: This study aimed to assess the commutability of frozen pooled human serum (PHS), high concentration of Immunoglobulin M (IgM) pure diluted materials (HPDM), commercialized pure materials (CPM), and dilutions of ERM-DA470k/IFCC in IgM detection using the CLSI and IFCC approaches, to support standardization or harmonization of IgM measurement. METHODS: Twenty-four serum samples, relevant reference materials (PHS, HPDM, CPM), and different ERM-DA470k/IFCC dilutions were analyzed in triplicate using six routine methods. The commutability of the relevant reference materials was carried out following CLSI EP30-A and IFCC bias analysis. RESULTS: According to the CLSI approach, low, medium, and high concentrations of PHS, HPDM, and CPM were commutable on 10, 13, 15, 13, and 8 of 15 assay combinations, respectively. Using the IFCC approach, low, medium, and high concentrations of PHS, HPDM, and CPM were commutable on 10, 11, 9, 15, and 10 of 15 assay combinations, respectively. The ERM-DA470k/IFCC dilutions with D-PBS and RPMI-1640 Medium were commutable on 13 of 15 assay combinations according to CLSI and were commutable on all 15 assay combinations using IFCC approach. CONCLUSIONS: High concentration of PHS were commutable on all six detection systems using the CLSI approach. Low and medium concentration of PHS showed unsatisfied commutability. HPDM, not CPM have good commutability, has the potential to become reference materials. ERM-DA470k/IFCC diluted with different medium showed different commutability.

Matrix Matters: Assessment of Commutability among BK Virus Assays and Standards.

Quantitative testing of BK virus (BKPyV) nucleic acid has become the standard of care in transplant patients. While the relationship between interassay harmonization and commutability has been well characterized for other transplant-related viruses, it has been less well studied for BKPyV, particularly regarding differences in commutability between matrices. Here, interassay agreement was evaluated among six real-time nucleic acid amplification tests (NAATs) and one digital PCR (dPCR) BKPyV assay. Differences in the commutability of three quantitative standards was examined across all assays using a variety of statistical approaches. Panels, including 40 samples each of plasma and urine samples previously positive for BKPyV, together with one previously negative plasma sample and four previously negative urine samples, were tested using all assays, with each real-time NAAT utilizing its usual quantitative calibrators. Serial dilutions of WHO, National Institute for Standards and Technology (NIST), and commercially produced (Exact/Bio-Rad) reference materials were also run by each assay as unknowns. The agreement of the clinical sample values was assessed as a group and in a pairwise manner. The commutability was estimated using both relativistic and quantitative means. The quantitative agreement across assays in the urine samples was within a single log10 unit across all assays, while the results from the plasma samples varied by 2 to 3 log10 IU/mL. The commutability showed a similar disparity between the matrices. Recalibration using international standards diminished the resulting discrepancies in some but not all cases. Differences in the sample matrix can affect the commutability and interassay agreement of quantitative BKPyV assays. Differences in commutability between matrices may largely be due to factors other than those such as amplicon size, previously described as important in the case of cytomegalovirus. Continued efforts to standardize viral load measurements must address multiple sources of variability and account for differences in assay systems, quantitative standards, and sample matrices.

Harmonization Status of Serum Ferritin Measurements and Implications for Use as Marker of Iron-Related Disorders.

BACKGROUND: Serum ferritin is considered a suitable biomarker of iron-related disorders. However, data about the comparability of results among commercial measuring systems (MSs) are contradictory. We performed an intercomparison study aimed at verifying the current interassay variability and its impact on clinical application of the test. Obtaining this information is vital because manufacturers continue to claim calibration alignment to different WHO preparations, which are not related to each other in terms of traceability. METHODS: Four widely used MSs were evaluated. The interassay agreement was verified using 39 human serum pools. The recovery of WHO International Standard (IS) 94/572 (the only reference material available at the time of the study) was evaluated, after assessing the material commutability. Finally, an approach for harmonizing ferritin results was proposed. RESULTS: Highly significant differences (P < 0.00001) among ferritin concentrations assayed by different MSs were detected and the interassay CV (median 22.9%; interquartile range 21.8-25.5) overlapped the desirable intermethod bias (24.6%). IS 94/572 was commutable for use only with Access and Centaur, with Access being the only MS correctly recovering its assigned value. Accordingly, we used regression data against Access to recalibrate MSs, indirectly aligning them to IS 94/572, with a substantial improvement in degree of harmonization and traceability to higher-order reference. CONCLUSIONS: The harmonization among evaluated ferritin MSs is far from optimal, with the implementation of traceability to different WHO ISs being a factor of confusion. A recalibration approach, however, would permit measurement harmonization, allowing the use of common decision thresholds.

Metrological traceability and clinical traceability of laboratory results - the role of commutability in External Quality Assurance.

The role of an External Quality Assurance (EQA) program is generally seen as providing a service to routine laboratories that their analytical performance is satisfactory and stimulating corrective action in the event of poor results. It is recognised that an ideal EQA program uses materials that are commutable with patient samples and have values assigned by higher-order reference methods. Despite this, most routine EQA programs use materials without verified commutability and use consensus means (based on either peer group or all laboratories) as target values. We propose an ongoing role for EQA programs using non-commutable materials and consensus targets to support the measurement services of routine laboratories. This is provided the relevant comparators supplied by the laboratory, e.g. reference intervals and clinical decision points, are based on the same or equivalent measurement system as is used by the laboratory. Materials without verified commutability often have certain practical advantages, which may include the range of analyte concentrations, verified stability, replicate samples and, significantly, lower costs. Laboratories using such programs need to be aware of the limitations, especially comparing results from different measurement systems. However, we also recognise that as well as individual laboratories, data from EQA programs informs manufacturers, professional organisations, clinical guideline writers and other medical bodies For consideration beyond an individual laboratory, proper assessment of differences between measurement systems (results harmonization) and demonstration of correct implementation of metrological traceability (methods trueness) become vital, and for that purpose, commutability of EQA materials and traceability of target values are required.

Performance of four regression frameworks with varying precision profiles in simulated reference material commutability assessment.

OBJECTIVES: One approach to assessing reference material (RM) commutability and agreement with clinical samples (CS) is to use ordinary least squares or Deming regression with prediction intervals. This approach assumes constant variance that may not be fulfilled by the measurement procedures. Flexible regression frameworks which relax this assumption, such as quantile regression or generalized additive models for location, scale, and shape (GAMLSS), have recently been implemented, which can model the changing variance with measurand concentration. METHODS: We simulated four imprecision profiles, ranging from simple constant variance to complex mixtures of constant and proportional variance, and examined the effects on commutability assessment outcomes with above four regression frameworks and varying the number of CS, data transformations and RM location relative to CS concentration. Regression framework performance was determined by the proportion of false rejections of commutability from prediction intervals or centiles across relative RM concentrations and was compared with the expected nominal probability coverage. RESULTS: In simple variance profiles (constant or proportional variance), Deming regression, without or with logarithmic transformation respectively, is the most efficient approach. In mixed variance profiles, GAMLSS with smoothing techniques are more appropriate, with consideration given to increasing the number of CS and the relative location of RM. In the case where analytical coefficients of variation profiles are U-shaped, even the more flexible regression frameworks may not be entirely suitable. CONCLUSIONS: In commutability assessments, variance profiles of measurement procedures and location of RM in respect to clinical sample concentration significantly influence the false rejection rate of commutability.

Commutability assessment of reference materials for homocysteine.

OBJECTIVES: Commutability of reference materials is essential for ensuring the traceability of patient measurement results and the technical basis for the use of reference materials. Commutability is only relevant for matrixed reference material; it is a prerequisite for the accuracy and authenticity of calibration methods. In this study, we evaluated the commutability of reference materials for homocysteine. METHODS: Five conventional measurement methods were applied to simultaneously measure 30 serum samples and seven homocysteine reference materials from the National Institute of Standards and Technology and the National Institute of Metrology. Liquid chromatography tandem-mass spectrometry was used as a reference method. Two methods were used to evaluate the commutability of the seven reference materials according to the Clinical and Laboratory Standards Institute EP30-A and the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) commutability assessment document. RESULTS: Among 35 combinations of the five conventional methods and seven reference materials, after evaluation in accordance with the EP30-A, the seven reference materials passed the commutability assessment, and 34 combinations were commutable. According to the IFCC, the commutability evaluation of 28 combinations was conclusive (commutable or non-commutable), while results for the remaining seven combinations could not be determined. CONCLUSIONS: The homocysteine reference materials showed good commutability. The sensitivity of the measurement procedure, measurement deviation and uncertainty, and differences in the "measurand" selected by different methods may affect the evaluation results. Additionally, different judgment standards for different methods may explain the observed variations in evaluation results.

Comparison and commutability study between standardized liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) and chemiluminescent enzyme immunoassay for aldosterone measurement in blood.

A commutability confirmation test for the blood aldosterone measurement was performed on liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) as a designated comparison method (DCM) and four chemiluminescent enzyme immunoassay (CLEIA) measurement procedures based on metrological traceability. A conventional radioimmunoassay (RIA) and two measurement procedures of CLEIA which obtains RIA equivalent values were also compared. The relationship between the DCM value and the CLEIA value with respect to 120 pg/mL of the RIA value, which is the screening criterion of primary aldosteronism (PA) was clarified. For the correlation test, 75 samples of patient serum and plasma were used. Regression analysis revealed that the standardized LC-MS/MS and four CLEIA measurement procedures were in good agreement. This is the effect of measurement specificity and calibration using by certified reference material (CRM). The median of the LC-MS/MS corresponding to 120 pg/mL of RIA was 48.5 pg/mL. In the mean of standardized four CLEIA values corresponding to the 48.5 pg/mL of LC-MS/MS value was 47.51 pg/mL and the standard deviation (SD) was 2.93 pg/mL. However, the correlation between the RIA value and the RIA equivalent of the two measurement procedures by CLEIA differed depending on the measurement procedure. This is due to the influence of RIA measurement performance. Standardized CLEIA measurements are suitable for routine measurement procedure. When converting the LC-MS/MS equivalent value by the standardized CLEIA to the conventional RIA value, it is necessary to use the conversion formula.

A candidate reference method and multiple commutable control materials for serum 25-hydroxyvitamin D measurement.

OBJECTIVES: The aim of the current study was to establish a reliable candidate reference method for serum 25-hydroxyvitamin D [25(OH)D] measurement and to assess the commutability of multiple control materials among liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. METHODS: Serum 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] together with spiked internal standards were extracted with a one-step approach and then analyzed by LC-MS/MS. The commutability assessment for 25(OH)D was conducted according to the Clinical and Laboratory Standards Institute (CLSI) EP14-A3 protocol. 25(OH)D concentrations in 5 levels of unprocessed serum pools, 7 levels of serum pools spiked with 25(OH)D3 or 25(OH)D2, 3 levels of commercial control materials, 2 levels of spiked bovine serum, and 4 levels of external quality assessment (EQA) materials were measured along with 30 single-donor samples using the candidate reference method and two routine LC-MS/MS methods. RESULTS: The candidate reference method could separate 25(OH)D2 and 25(OH)D3 from 14 potential interfering compounds completely within a 9-min analysis time. Good method precision was obtained, and measurement results on certified reference material NIST SRM 972a were within the uncertainty of the certified values. All candidate materials were assessed commutable for LC-MS/MS methods. CONCLUSIONS: The candidate reference method for serum 25(OH)D measurement is precise, accurate, and robust against interferences and can provide an accuracy base for routine methods. The multiple alternative control materials with commutability among LC-MS/MS methods will facilitate the further standardization for serum 25(OH)D measurement.

Optimizing Available Tools for Achieving Result Standardization: Value Added by Joint Committee on Traceability in Laboratory Medicine (JCTLM).

BACKGROUND: The JCTLM created a Task Force on Reference Measurement System Implementation (TF-RMSI) to provide guidance on metrological traceability implementation for the in vitro diagnostics (IVD) community. CONTENT: TF-RMSI investigated the reference measurement systems (RMS) for 13 common measurands by applying the following procedural steps: (a) extracting data from the JCTLM database of available certified reference materials (CRMs) and reference measurement procedures (RMPs); (b) describing the RMS to which each recruited CRM or RMP belongs; (c) identifying the intended use of the CRMs, and, if used as a common calibrator for IVD measuring systems and/or trueness assessment of field methods was included, checking the CRM's certificate for information about commutability with clinical samples; and (d) checking if the CRM or RMP measurement uncertainty (MU) has the potential to be small enough to avoid significantly affecting the analytical performance specifications (APS) for MU of clinical sample results when the MU from the IVD calibrator and from the end-user measuring system were combined. SUMMARY: We produced a synopsis of JCTLM-listed higher-order CRMs and RMPs for the selected measurands, including their main characteristics for implementing traceability and fulfilling (or not) the APS for suitable MU. Results showed that traceability to higher-order references can be established by IVD manufacturers within the defined APS for most of the 13 selected measurands. However, some measurands do not yet have suitable CRMs for use as common calibrators. For these measurands, splitting clinical samples with a laboratory performing the RMP may provide a practical alternative for establishing a calibration hierarchy.

Measurement of urine albumin by liquid chromatography-isotope dilution tandem mass spectrometry and its application to value assignment of external quality assessment samples and certification of reference materials.

OBJECTIVES: Urine albumin is measured in clinical laboratories by immunoturbidimetry. However, large biases are observed among the different routine methods. To standardize the measurement of urine albumin, a reference measurement procedure (RMP) and urine albumin certified reference materials (CRMs) are needed. METHODS: A candidate RMP for urine albumin based on liquid chromatography-isotope dilution tandem mass spectrometry (LC-IDMS/MS) using human serum albumin as calibration standard was developed. Isotope-labeled human albumin was used as internal standard. Urine samples were digested using trypsin and eight resulting "signature" peptides of albumin were quantified by LC-IDMS/MS. The candidate RMP was employed in value assignment of external quality assessment (EQA) samples and certification of urine albumin reference materials. The commutability of the developed CRMs was assessed against patient samples. RESULTS: The candidate RMP (recovery 101.5-103.2% and CV 1.2-3.3% at about 7-40 mg/L) met optimal performance goal. The lower limit of quantification was 0.03 mg/L as determined by signal-to-noise method. The EQA results from clinical laboratories using different immunoturbidimetric methods were generally comparable with assigned target values determined by the candidate RMP, with albumin concentrations ranging from 5 to 226 mg/L. Urine albumin reference materials (two levels) certified using the candidate RMP showed good commutability in a preliminary study. CONCLUSIONS: With optimal method precision and trueness, as well as comparability with routine methods, the developed RMP may be used for value assignment of EQA samples or certification of reference materials, which are important pillars in urine albumin method standardization.