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

Establishment and clinical application of a candidate reference measurement procedure for quantification of urinary vanillylmandelic acid and homovanillic acid using ID-LC-MS/MS method

Neuroblastoma (NB), an embryonic tumor of the autonomous nervous system, poses a significant threat to the health and lives of children. Accurate measurement of vanillylmandelic acid (VMA) and homovanillic acid (HVA) in human urine is crucial for screening and diagnosis of NB. Although various laboratories have developed liquid chromatography tandem mass spectrometry (LC-MS/MS) method to detect VMA and HVA, the comparability between the results obtained from different laboratories and methods was poor. The absence of reference method for VMA and HVA hinders the standardization of their measurements. Therefore, a candidate reference measurement procedure (cRMP) based on isotope dilution LC-MS/MS (ID-LC-MS/MS) for the detection of VMA and HVA in human urine was established. Urine samples were spiked with VMA-d3 and HVA-d5 as internal standards and extracted using a protein precipitation method. The cRMP exhibited desirable precision with the total imprecision below 5 %. The accuracy of this cRMP was demonstrated by the high analytical recovery (98.64 % - 102.22 % and 98.41 % - 100.97 % for VMA and HVA, respectively), and comparability between different reference systems. The limit of detection for HVA and VMA were 15.625 ng/mL and 3.906 ng/mL, respectively; the quantification limits were 62.5 ng/mL and 7.813 ng/mL, respectively, which can meet the clinical detection requirements. The linear range was from 78.125 ng/mL to 20 μg/mL. Specificity evaluations showed no corresponding interference from structurally similar analogs. In conclusion, we have established a cRMP based on ID-LC-MS/MS for the measurement of VMA and HVA in urine samples, demonstrating well-defined method performance including accuracy, precision, and specificity. This newly established cRMP is suitable for routine assay standardization and evaluation of clinical samples. Furthermore, this method has the potential to significantly enhance the diagnostic accuracy for neuroblastoma.

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.

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

OBJECTIVES

An isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure (RMP) was developed and validated to accurately measure serum and plasma concentrations of carbamazepine.

METHODS

Quantitative nuclear magnetic resonance (qNMR) spectroscopy was used to determine the absolute content of the reference material, ensuring its traceability to SI units. The separation of carbamazepine from potential interferences, whether known or unknown, was achieved using a C18 column. A protein precipitation protocol followed by a high dilution step was established for sample preparation. Assay validation and determination of measurement uncertainty were performed in accordance with the guidelines of the Clinical and Laboratory Standards Institute, the International Conference on Harmonization (ICH), and the Guide to the Expression of Uncertainty in Measurement (GUM). In order to demonstrate equivalence to the already existing RMP a method comparison study was performed.

RESULTS

The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of carbamazepine within the range of 0.800-18.0 μg/mL. Intermediate precision and repeatability (n=60 measurements) was found to be <1.6 % and <1.3 % over all concentration levels and independent from the matrix. The relative mean bias ranged from -0.1 to 0.6 % for native serum and from -0.3 to -0.1 % for Li-heparin plasma levels. The measurement uncertainties for single measurements and target value assignment were found to be <1.8 % and <1.3 %, respectively. Method comparison showed a good agreement between the Joint Committee of Traceability in Laboratory Medicine (JCTLM) listed RMP and the candidate RMP resulting in a Passing-Bablok regression equation with a slope of 1.01 and an intercept of -0.01. The bias in the patient cohort was found to be 0.9 %.

CONCLUSIONS

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

OBJECTIVES

Primidone is an anticonvulsive drug used in the treatment of epilepsy and essential tremor. It offers beneficial effects in controlling seizures, but its usage is also associated with possible side effects. To ensure optimal therapy, it is crucial to measure its concentration through accurate quantification methods. Therefore, our main goal was to develop and validate a new reference measurement procedure (RMP) for accurately measuring primidone levels in human serum and plasma.

METHODS

In our study, we focused on the separation of primidone from both known and unknown interferences using a C18 column. To achieve accurate sample preparation, we developed a protocol involving protein precipitation followed by a high dilution step. The validation of the assay and determination of measurement uncertainty were carried out following guidelines from organizations such as the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the Expression of Uncertainty in Measurement. These rigorous validation processes ensure the reliability and accuracy of our method for quantifying primidone levels in human serum and plasma samples.

RESULTS

The RMP was shown to be highly selective and specific, with no evidence of matrix interference. It can be used to quantify primidone in the range of 0.150-30.0 μg/mL. Intermediate precision was less than 4.0 %, and repeatability CV ranged from 1.0 to 3.3 % across all concentration levels. The relative mean bias ranged from 0.1 to 3.9 % for native serum levels, and from -2.6 to 2.8 % for lithium-heparin plasma levels. The measurement uncertainties for single measurements and target value assignment were 1.5-4.1 % and 0.9-1.0 %, respectively.

CONCLUSIONS

In this study, we introduce an innovative LC-MS/MS-based candidate RMP specifically designed for primidone in human serum and plasma. Our RMP offers a traceable platform, facilitating the standardization of routine assays and enabling the evaluation of clinically relevant samples. With this novel approach, we aim to enhance the accuracy and reliability of primidone measurements, ultimately benefiting the field of clinical research and patient care.

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.

Insight into the status of plasma renin and aldosterone measurement: findings from 526 clinical laboratories in China

OBJECTIVES

Accurate measurements of renin and aldosterone levels play an important role in primary aldosteronism screening, which is of great importance in the management and categorization of hypertension. The objective of this study is to investigate the current status of plasma renin and aldosterone measurements in China, which is achieved by analyzing the results of 526 clinical laboratories nationwide for three pooled fresh plasma samples derived from more than 2,000 patients.

METHODS

Renin and aldosterone in three pooled plasma samples were measured four times in 526 laboratories employing various measurement systems. The inter- and intra-laboratory %CV were calculated and compared. To determine the source of the substantial inter-laboratory %CV, laboratories were categorized according to the measurement systems they are using, and both the inter- and intra-measurement-system %CV were calculated and compared.

RESULTS

Regarding renin, the majority of laboratories use four primary commercial immunoassays. However, for aldosterone, in addition to commercial immunoassays, laboratory-developed liquid chromatography-tandem mass spectrometry (LC-MS) methods are also used by laboratories. The median values of intra-laboratory %CVs, intra-measurement-system %CVs, inter-laboratory %CVs, and inter-measurement systems %CVs varied between 1.6 and 2.6 %, 4.6 and 14.9 %, 8.3 and 25.7 %, and 10.0 and 34.4 % for renin, respectively. For aldosterone, these values ranged from 1.4 to 2.2 %, 2.5-14.7 %, 9.9-31.0 %, and 10.0-35.5 %, respectively.

CONCLUSIONS

The precision within laboratories and measurement systems for plasma renin and aldosterone measurements is satisfactory. However, the comparability between laboratories using different measurement systems remains lacking, indicating the long way to achieve standardization and harmonization for these two analytes.

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.