An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of carbamazepine-10,11-epoxide in human serum and plasma

OBJECTIVES

A reference measurement procedure (RMP) using isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) was developed and validated with the aim of accurately measuring carbamazepine-10,11-epoxide concentrations in human serum and plasma.

METHODS

To establish traceability to SI units, the absolute content of the reference material was determined using quantitative nuclear magnetic resonance (qNMR) spectroscopy. As sample preparation a protein precipitation protocol followed by a high dilution step was established. Chromatographic separation from carbamazepine and potential metabolites was achieved using a C18 stationary phase. Selectivity, specificity, matrix effects, precision and accuracy, inter-laboratory equivalence, and uncertainty of measurement were evaluated based on guidelines from the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the Expression of Uncertainty in Measurement.

RESULTS

The RMP demonstrated very good selectivity and specificity, showing no evidence of a matrix effect. This enabled accurate quantification of carbamazepine-epoxide in the concentration range of 0.0400-12.0 μg/mL. The intermediate precision was found to be less than 2.1 %, and the repeatability coefficient of variation (CV) ranged from 1.2 to 1.8 % across all concentration levels. Regarding accuracy, the relative mean bias varied from 1.4 to 2.5 % for native serum levels and from 1.4 to 3.5 % for Li-heparin plasma levels. The measurement uncertainty for single measurements ranged from 1.6 to 2.1 %.

CONCLUSIONS

In this study, we introduce a new LC-MS/MS-based candidate RMP for accurately measuring carbamazepine-10,11-epoxide in human serum and plasma. This novel method offers a traceable and dependable platform, making it suitable for standardizing routine assays and assessing clinically relevant samples.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) for the quantification of phenobarbital in human serum and plasma

OBJECTIVES

Phenobarbital serves as an antiepileptic drug (AED) and finds application in the treatment of epilepsy either as monotherapy or adjunctive therapy. This drug exhibits various pharmacodynamic properties that account for its beneficial effects as well as potential side effects. Accurate measurement of its concentration is critical for optimizing AED therapy through appropriate dose adjustments. Therefore, our objective was to develop and validate a new reference measurement procedure (RMP) for the accurate quantification of phenobarbital levels in human serum and plasma.

METHODS

A sample preparation protocol based on protein precipitation followed by a high dilution step was established in combination with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method using a C8 column to separate target analytes from known and unknown interferences. Assay validation and determination of measurement uncertainty were performed based on current guidelines. Selectivity and Specificity were assessed using spiked serum and plasma samples; to investigate possible matrix effects (MEs) a post-column infusion experiment and a comparison of standard line slopes was performed. Precision and accuracy were determined within a multiday precision experiment.

RESULTS

The RMP was shown to be highly selective and specific, with no evidence of matrix interferences. It can be used to quantify phenobarbital in the range of 1.92 to 72.0 μg/mL. Intermediate precision was less than 3.2 %, and repeatability coefficient of variation (CV) ranged from 1.3 to 2.0 % across all concentration levels. The relative mean bias ranged from -3.0 to -0.7 % for native serum levels, and from -2.8 to 0.8 % for Li-heparin plasma levels. The measurement uncertainties (k=1) for single measurements and target value assignment were 1.9 to 3.3 % and 0.9 to 1.6 %, respectively.

CONCLUSIONS

A novel LC-MS/MS-based candidate RMP for the quantification of phenobarbital in human serum and plasma is presented which can be used for the standardization of routine assays and the evaluation of clinically relevant samples.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of zonisamide in human serum and plasma

OBJECTIVES

To describe and validate an isotope dilution-liquid chromatograph-tandem mass spectrometry (ID-LC-MS/MS) based reference measurement procedure (RMP) for zonisamide to accurately measure serum and plasma concentrations.

METHODS

Quantitative nuclear magnetic resonance (qNMR) spectroscopy was employed to determine the absolute content of the reference material used in order to establish traceability to SI units. Separation of zonisamide from known or unknown interferences was performed on a C8 column. For sample preparation a protocol based on protein precipitation in combination with a high dilution step was established. Assay validation and determination of measurement uncertainty were performed based on guidelines from the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the expression of uncertainty in measurement.

RESULTS

The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of zonisamide within the range of 1.50-60.0 μg/mL. Intermediate precision was <1.4 % and repeatability CV ranged from 0.7 to 1.2 % over all concentration levels. The relative mean bias ranged from 0.0 to 0.8 % for native serum levels and from 0.2 to 2.0 % for Li-heparin plasma levels. The measurement uncertainties for single measurements and target value assignment ranged from 1.1 to 1.4 % and 0.8-1.0 %, respectively.

CONCLUSIONS

We present a novel LC-MS/MS-based candidate RMP for zonisamide in human serum and plasma which provides a traceable and reliable platform for the standardization of routine assays and evaluation of clinically relevant samples.

Developing an SI-traceable Lp(a) reference measurement system: a pilgrimage to selective and accurate apo(a) quantification

In the past decade a remarkable rebirth of serum/plasma lipoprotein(a) (Lp(a)) as an independent risk factor of cardiovascular disease (CVD) occurred. Updated evidence for a causal continuous association in different ethnic groups between Lp(a) concentrations and cardiovascular outcomes has been published in the latest European Atherosclerosis Society (EAS) Lp(a) consensus statement. Interest in measuring Lp(a) at least once in a person's lifetime moreover originates from the development of promising new Lp(a) lowering drugs. Accurate and clinically effective Lp(a) tests are of key importance for the timely detection of high-risk individuals and for future evaluation of the therapeutic effects of Lp(a) lowering medication. To this end, it is necessary to improve the performance and standardization of existing Lp(a) tests, as is also noted in the Lp(a) consensus statement. Consequently, a state-of-the-art internationally endorsed reference measurement system (RMS) must be in place that allows for performance evaluation of Lp(a) field tests in order to certify their validity and accuracy. An ELISA-based RMS from Northwest Lipid Research Laboratory (University of Washington, Seattle, USA) has been available since the 1990s. A next-generation apo(a)/Lp(a) RMS is now being developed by a working group from the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). The envisioned apo(a) RMS is based on the direct measurement of selected proteotypic fragments generated after proteolytic digestion using quantitative protein mass spectrometry (MS). The choice for an MS-based RMS enables selective measurement of the proteotypic peptides and is by design apo(a) isoform insensitive. Clearly, the equimolar conversion of apo(a) into the surrogate peptide measurands is required to obtain accurate Lp(a) results. The completeness of proteolysis under reaction conditions from the candidate reference measurement procedure (RMP) has been demonstrated for the quantifying apo(a) peptides. Currently, the candidate apo(a) RMP is endorsed by the IFCC and recommendations for suitable secondary reference materials have been made in a recent commutability study paper. Ongoing efforts toward a complete apo(a) RMS that is listed by the Joint Committee on Traceability in Laboratory Medicine (JCTLM) are focused on the peptide-based calibration and the establishment of a network of calibration laboratories running the apo(a) RMS in a harmonized way. Once completed, it will be the holy grail for evaluation and certification of Lp(a) field methods.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) for the quantification of aldosterone in human serum and plasma

OBJECTIVES

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC MS/MS)-based candidate reference measurement procedure (RMP) for aldosterone quantification in human serum and plasma is presented.

METHODS

The material used in this RMP was characterized by quantitative nuclear magnetic resonance (qNMR) to assure traceability to SI Units. For liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis a two-dimensional heart cut LC approach, in combination with an optimal supported liquid extraction protocol, was established for the accurate analysis of aldosterone in human serum and plasma in order to minimize matrix effects and avoid the co-elution of interferences. Assay validation was performed according to current guidelines. Selectivity and specificity were assessed using spiked serum; potential matrix effects were examined by a post column infusion experiment and the comparison of standard line slopes. An extensive protocol over 5 days was applied to determine precision, accuracy and trueness. Measurement uncertainty was evaluated according to the Guide to the Expression of Uncertainty in Measurement (GUM), for which three individual sample preparations were performed on at least two different days.

RESULTS

The RMP allowed aldosterone quantification within the range of 20-1,200 pg/mL without interference from structurally-related compounds and no evidence of matrix effects. Intermediate precision was ≤4.7% and repeatability was 2.8-3.7% for all analyte concentrations. The bias ranged between -2.2 and 0.5% for all levels and matrices. Total measurement uncertainties for target value assignment (n=6) were found to be ≤2.3%; expanded uncertainties were ≤4.6% (k=2) for all levels.

CONCLUSIONS

The RMP showed high analytical performance for aldosterone quantification in human serum and plasma. The traceability to SI units was established by qNMR content determination of aldosterone, which was utilized for direct calibration of the RMP. Thus, this candidate RMP is suitable for routine assay standardization and evaluation of clinical samples.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of levetiracetam in human serum and plasma

OBJECTIVES

To develop an isotope dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based candidate reference measurement procedure (RMP) for levetiracetam quantification in human serum and plasma.

METHODS

Quantitative nuclear magnetic resonance spectroscopy (qNMR) was used to characterize the RMP material to ensure traceability to SI units. To quantify levetiracetam, an LC-MS/MS method was optimized using a C8 column for chromatographic separation following protein-precipitation-based sample preparation. Spiked matrix samples of serum and plasma were used to test selectivity and specificity. Matrix effects were determined by performing a post-column infusion experiment and comparing standard line slopes. Precision and accuracy were evaluated over 5 days. Measurement uncertainty was evaluated according to the Guide to the Expression of Uncertainty in Measurement (GUM).

RESULTS

The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of levetiracetam within the range of 1.53-90.0 μg/mL. Intermediate precision was <2.2% and repeatability was 1.1-1.7% across all concentrations. The relative mean bias ranged from -2.5% to -0.3% across all levels and matrices within the measuring range. Diluted samples were found with a mean bias ranging from -0.1 to 2.9%. The predefined acceptance criterion for measurement uncertainty was met and determined for individual measurements independently of the concentration level and sample type to be ≤4.0% (k=2).

CONCLUSIONS

We present a novel LC-MS/MS)-based candidate RMP for levetiracetam in human serum and plasma. Its expanded measurement uncertainty of ≤4.0% meets the clinical needs in levetiracetam monitoring. Utilizing qNMR to characterize levetiracetam reference materials allowed metrological traceability to SI units.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of topiramate in human serum and plasma

OBJECTIVES

Topiramate is an antiepileptic drug (AED) used for the monotherapy or adjunctive treatment of epilepsy and for the prophylaxis of migraine. It has several pharmacodynamic properties that contribute to both its clinically useful properties and observed adverse effects. Accurate measurement of its concentration is therefore essential for dose adjustment/optimisation of AED therapy. Our aim was to develop and validate a novel reference measurement procedure (RMP) for the quantification of topiramate in human serum and plasma.

METHODS

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method in combination with a protein-precipitation-based sample preparation allows for quantification of topiramate in human serum and plasma. To assure traceability to SI units, quantitative nuclear magnetic resonance (qNMR) was applied to characterize the reference material used as primary calibrator for this RMP. Matrix effects were determined by performing a post-column infusion experiment and comparing standard line slopes. Accuracy and precision was evaluated performing an extensive five day precision experiment and measurement uncertainty was evaluated according Guide to the Expression of Uncertainty in Measurement (GUM).

RESULTS

The method enabled topiramate quantification within the range of 1.20-36.0 μg/mL without interference from structurally related compounds and no evidence of a matrix effect. Intermediate precision was ≤3.2 % and repeatability was 1.4-2.5 % across all concentration levels. The relative mean bias was -0.3 to 3.5 %. Expanded measurement uncertainties for target value assignment (n=6) were found to be ≤2.9 % (k=2) independent of the concentration level and the nature of the sample.

CONCLUSIONS

In human serum and plasma, the RMP demonstrated high analytical performance for topiramate quantification and fulfilled the requirements on measurement uncertainty. Traceability to SI units was established by qNMR content determination of the topiramate, which was used for direct calibration of the RMP. This RMP is, therefore, fit for purpose for routine assay standardization and clinical sample evaluation.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) for the quantification of gabapentin in human serum and plasma

OBJECTIVES

To describe and validate a reference measurement procedure (RMP) for gabapentin, employing quantitative nuclear magnetic resonance (qNMR) spectroscopy to determine the absolute content of the standard materials in combination with isotope dilution-liquid chromatograph-tandem mass spectrometry (ID-LC-MS/MS) to accurately measure serum and plasma concentrations.

METHODS

A sample preparation protocol based on protein precipitation in combination with LC-MS/MS analysis using a C8 column for chromatographic separation was established for the quantification of gabapentin. Assay validation and determination of measurement uncertainty were performed according to guidance from the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the expression of uncertainty in measurement. ID-LC-MS/MS parameters evaluated included selectivity, specificity, matrix effects, precision and accuracy, inter-laboratory equivalence, and uncertainty of measurement.

RESULTS

The use of qNMR provided traceability to International System (SI) units. The chromatographic assay was highly selective, allowing baseline separation of gabapentin and the gabapentin-lactam impurity, without observable matrix effects. Variability between injections, preparations, calibrations, and days (intermediate precision) was <2.3%, independent of the matrix, while the coefficient of variation for repeatability was 0.9-2.0% across all concentration levels. The relative mean bias ranged from -0.8-1.0% for serum and plasma samples. Passing-Bablok regression analysis indicated very good inter-laboratory agreement; the slope was 1.00 (95% confidence interval [CI] 0.98 to 1.03) and the intercept was -0.05 (95% CI -0.14 to 0.03). Pearson's correlation coefficient was ≥0.996. Expanded measurement uncertainties for single measurements were found to be ≤5.0% (k=2).

CONCLUSIONS

This analytical protocol for gabapentin, utilizing traceable and selective qNMR and ID-LC-MS/MS techniques, allows for the standardization of routine tests and the reliable evaluation of clinical samples.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) for the quantification of methotrexate in human serum and plasma

OBJECTIVES

To develop an isotope dilution-liquid chromatography-tandem mass spectrometry-(ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) for quantification of methotrexate in human serum and plasma.

METHODS

Quantitative nuclear magnetic resonance (qNMR) was used to determine absolute methotrexate content in the standard. Separation was achieved on a biphenyl reversed-phase analytical column with mobile phases based on water and acetonitrile, both containing 0.1% formic acid. Sample preparation included protein precipitation in combination with high sample dilution, and method validation according to current guidelines. The following were assessed: selectivity (using analyte-spiked samples, and relevant structural-related compounds and interferences); specificity and matrix effects (via post-column infusion and comparison of human matrix vs. neat samples); precision and accuracy (in a five-day validation analysis). RMP results were compared between two independent laboratories. Measurement uncertainty was evaluated according to current guidelines.

RESULTS

The RMP separated methotrexate from potentially interfering compounds and enabled measurement over a calibration range of 7.200-5,700 ng/mL (0.01584-12.54 μmol/L), with no evidence of matrix effects. All pre-defined acceptance criteria were met; intermediate precision was ≤4.3% and repeatability 1.5-2.1% for all analyte concentrations. Bias was -3.0 to 2.1% for samples within the measuring range and 0.8-4.5% for diluted samples, independent of the sample matrix. RMP results equivalence was demonstrated between two independent laboratories (Pearson correlation coefficient 0.997). Expanded measurement uncertainty of target value-assigned samples was ≤3.4%.

CONCLUSIONS

This ID-LC-MS/MS-based approach provides a candidate RMP for methotrexate quantification. Traceability of methotrexate standard and the LC-MS/MS platform were assured by qNMR assessment and extensive method validation.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) for the quantification of lamotrigine in human serum and plasma

OBJECTIVES

We developed an isotope dilution (ID)-liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based candidate reference measurement procedure (RMP) for lamotrigine in human serum and plasma, using quantitative nuclear magnetic resonance-characterized reference standards to ensure traceability to the International System of Units.

METHODS

A sample preparation protocol based on protein precipitation combined with LC-MS/MS analysis using a C18 column for chromatographic separation was established for the quantification of lamotrigine in human serum and plasma. Assay validation was performed according to current guidelines. Spiked serum and plasma samples were used to assess selectivity and specificity; a post-column infusion experiment and comparison of standard line slopes were performed to ascertain possible matrix effects. Precision and accuracy were determined in a 5 days validation experiment. Measurement uncertainty was determined per the Guide to the Expression of Uncertainty in Measurement.

RESULTS

The method allowed the quantification of lamotrigine in serum and plasma in a range of 0.600-24.0 μg/mL without any observable matrix effects. The relative mean bias (n=6) ranged from 1.7 to 3.7%; intermediate precision, including variances in between-day, -calibration, and -injection, was ≤2.4%, independent of the level and matrix. Total measurement uncertainty for a single measurement was ≤2.6%; expanded uncertainty was ≤5.2% (coverage factor k=2).

CONCLUSIONS

This candidate RMP based on ID-LC-MS/MS provides a traceable and reliable platform for the standardization of routine assays and the evaluation of clinical samples.

Validation of an LC-MS/MS Method Using Solid-Phase Extraction for the Quantification of 1-84 Parathyroid Hormone: Toward a Candidate Reference Measurement Procedure

BACKGROUND

Parathyroid hormone (PTH) measurement is important for patients with disorders of calcium metabolism, including those needing bone-turnover monitoring due to chronic kidney disease-mineral bone disorder. There are currently 2 generations of PTH immunoassays on the market, both having cross-reactivity issues and lacking standardization. Therefore, we developed an LC-MS/MS higher-order method for PTH analysis.

METHODS

The method was calibrated against the international standard for 1-84 PTH (WHO 95/646). Antibody-free sample preparation with the addition of an isotope-labeled internal standard was performed by solid-phase extraction. Extracts were analyzed by LC-MS/MS. EDTA-K2 plasma was used throughout the development and validation. Bias and uncertainty sources were tested according to ISO 15193. Clinical Laboratory Standards Institute guidelines and reference measurement procedures were consulted for the design of the validation. Patient samples and external quality controls were compared between LC-MS/MS and 2 third-generation immunoassays.

RESULTS

The method was validated for 1-84 PTH from 5.7 to 872.6 pg/mL. The interassay imprecision was between 1.2% and 3.9%, and the accuracy ranged from 96.2% to 103.2%. The measurement uncertainty was <5.6%. The comparison between LC-MS/MS and the immunoassays showed a proportional bias but moderate to substantial correlation between methods.

CONCLUSIONS

This LC-MS/MS method, which is independent of antibodies, is suitable for a wide range of PTH concentrations. The obtained analytical performance specifications demonstrate that development of a reference measurement procedure will be possible once a higher order reference standard is available.

Effect of the reaction temperature on the prothrombin time and the apparent International Normalized Ratio determined with International Standards for thromboplastins

Introduction

The definition of the International Normalized Ratio (INR) depends on a reference measurement procedure for the prothrombin time (PT) determined with international standards for thromboplastins. The agreed water bath temperature for PT determination in the reference measurement procedure is 37°C. The aim of the study was to assess the influence of small deviations of the agreed reaction temperature on PT and INR determined with World Health Organization international standards for thromboplastins rTF/16 (recombinant human) and RBT/16 (rabbit brain).

Methods

Prothrombin time was determined, with a manual hook technique, in glass test tubes in a water bath at a controlled temperature. The PT reaction temperatures were varied between 28 and 40°C. Pooled normal plasma and pooled coumarin plasma (INR ≈ 2.8) were used as test plasmas. The data were fitted to a quadratic relationship between PT and temperature.

Results

Prothrombin times with rTF/16 were shortened by increasing the reaction temperature up to approximately 39‐40°C. PTs with RBT/16 were shortened by increasing the reaction temperature up to approximately 34‐37°C, but were prolonged at higher temperatures. The apparent INR change of the coumarin plasma at 37.0°C was 0.06/°C and 0.11/°C for rTF/16 and RBT/16, respectively.

Conclusions

Reaction temperature had a significant effect on PT and the apparent INR with the International Standards. At 37.0°C, the apparent INR of coumarin plasma determined with RBT/16 was more responsive to temperature change than the apparent INR determined with rTF/16. The required accuracy of the water bath temperature should be 37.0 ± 0.1°C.

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.

Development of a designated comparison method for alkaline phosphatase measurements and its application to evaluating routine methods

The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) published the reference measurement procedure (RMP) for ALP measurement in 2011. However, the RMP is of high requirements for laboratories, complicated, time-consuming and high cost of reagents. Many manufacturers do not trace results to the higher procedure. And there is currently no designated comparison method (DCM) for ALP measurement. Thus, the standardization of ALP measurement is hindered. Automatic biochemical analyzers are easy to operate and widely used in clinical laboratories. Therefore, according to the RMP, establishing a DCM based on an automatic biochemical analyzer will be a practical way to establish traceability to the accuracy base and promote the standardization of ALP measurement. On the basis of conforming to the RMP recommended by IFCC as far as possible, the DCM was established based on a Thermo Indiko automatic biochemical analyzer. Performances of the method were validated. The DCM repeatability and within laboratory imprecision was <1% and <2.5%, respectively. For evaluation of trueness, the biases were within the equivalent limits. Measurement procedure comparisons and biases estimation were carried out between the DCM, the RMP, and the six routine methods using a panel of 40 individual human serum samples. The comparisons between the DCM and the RMP gave satisfying results. Compared with the DCM, the relative biases of some routine methods failed to meet the bias limit derived from biological variation.

Measurement of serum 17-hydroxyprogesterone using isotope dilution liquid chromatography-tandem mass spectrometry candidate reference method and evaluation of the performance for three routine methods

OBJECTIVES

Accurate measurements of serum 17-hydroxyprogesterone (17OHP) are essential for diagnosis and treatment monitoring for congenital adrenal hyperplasia patients. The performance of serum 17OHP routine methods remains highly variable that calls for a candidate reference measurement procedure (cRMP) to improve the standardization of serum 17OHP measurements.

METHODS

Serum samples spiked with internal standards were extracted with a combination of solid-phase extraction and liquid-liquid extraction. The 17OHP was quantified by the isotope dilution coupled with liquid chromatography/tandem mass spectrometry (ID-LC/MS/MS) with electrospray ionization in positive ion mode. Nine structural analogs of 17OHP were evaluated for interferences. The precision and analytical recovery were assessed. Twenty native and 40 spiked serum for performance evaluation were measured by the cRMP and two clinical LC/MS routine methods.

RESULTS

No apparent interferences were found with the 17OHP measurement. The within-run, between-run, and total precision for our method were 0.4-0.8%, 0.6-2.0%, and 1.0-2.1% for four pooled serum (2.46-102.72 nmol/L), respectively. The recoveries of added 17OHP were 100.0-100.2%. For the performance of two LC/MS routine methods, they showed relative deviation ranges of -22.1 to 1.1% and -6.7 to 12.8%, respectively.

CONCLUSIONS

We developed and validated a reliable serum 17OHP method using ID-LC/MS/MS. The desirable accuracy and precision of this method enable it to serve as a promising cRMP to improve the standardization for serum 17OHP routine measurements.

Task Force on CKD - We have Come a Long Way

Chronic Kidney Disease (CKD) is an important medical condition where diagnosis, staging and monitoring is largely based on routine laboratory tests. During the last 15 years there have been many important changes in the clinical management of CKD described in key international guidelines. In order to successfully implement these guidelines, laboratories must collaborate with clinicians to provide a co-ordinated service, including accurate measurements and of creatinine and urine albumin and reporting of an estimated glomerular filtration rate (eGFR). The IFCC/WASPaLM Task Force on Chronic Kidney Disease (TF-CKD) was established in 2008 and since that time has worked to improve laboratory testing in CKD. Key aspects of the work of the TF-CKD include supporting national laboratory medicine organisations to develop CKD testing guidelines, recognition of the vital role of collaboration between laboratory and clinical organisations, the importance of accurate measurements, and endorsement of the KDIGO 2012 CKD guidelines. A key function of the TF-CKD has been to facilitate sharing and learning between countries to provide the best outcomes.

Moving Toward Standardization of Urine Albumin Measurements

Measurement of urine albumin is important for detecting and monitoring kidney disease. At the present time, measurement of urine albumin is not standardized due to the lack of a reference system, which includes both a reference measurement procedure and certified reference materials. Developing a reference system will provide a means for clinical laboratory measurement procedures to become standardized and will enable successful use of uniform clinical decision points. Currently, urine albumin results vary in excess of 40% depending on which commercially available measurement procedure is utilized for measurement. Clinicians may struggle with classification of kidney disease in part due to differences in measurements from lack of agreement among laboratory methodologies employed when assessing urine albumin concentrations. This report focuses on current findings in urine albumin testing, highlights important measurement and reporting considerations, and presents strategies for developing a reference measurement procedure to enable standardization of urine albumin measurements.

An assessment of 25-hydroxyvitamin D measurements in comparability studies conducted by the Vitamin D Metabolites Quality Assurance Program

BACKGROUND

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health Office of Dietary Supplements, established the first accuracy-based program for improving the comparability of vitamin D metabolite measurements, the Vitamin D Metabolites Quality Assurance Program.

METHODS

The study samples were human serum or plasma Standard Reference Materials (SRMs) with 25-hydroxyvitamin D values that were determined at NIST. Participants evaluated the materials using immunoassay (IA), liquid chromatography (LC) with mass spectrometric detection, and LC with ultraviolet absorbance detection. NIST evaluated the results for concordance within the participant community as well as trueness relative to the NIST value.

RESULTS

For the study materials that contain mostly 25-hydroxyvitamin D3 (25(OH)D3),the coefficient of variation (CV) for the participant results was consistently in the range from 7% to 19%, and the median values were biased high relative to the NIST values. However, for materials that contain significant concentrations of both 25-hydroxyvitamin D2 (25(OH)D2) and 25(OH)D3, the median IA results were biased lower than both the LC and the NIST values, and the CV was as high as 28%. The first interlaboratory comparison results for SRM 972a Vitamin D Metabolites in Human Serum are also reported.

CONCLUSIONS

Relatively large within-lab and between-lab variability hinders conclusive assessments of bias and accuracy.

Modification of the IFCC reference measurement procedure for determination of HbA 1c by HPLC-ESI-MS

The reference measurement procedure for determination of HbA(1c) (glycated haemoglobin) using HPLC(high performance liquid chromatography)-ESI(electrospray ionisation)-MS(mass spectrometry) has been modified. Main modifications were a change in the buffer composition of the HPLC, a change in the gradient elution profile and the introduction of a post-column splitting system. The long-term stability of the HPLC-ESI-MS system proved to be of high importance to get reproducible results. Using the modified HPLC conditions stable retention times, high peak symmetry and a good column batch-to-batch reproducibility of the analytical results were obtained. The mean deviation from the target values was less than 0.7% with an imprecision of less than 2%.