Calibrating from Within: Multipoint Internal Calibration of a Quantitative Mass Spectrometric Assay of Serum Methotrexate

BACKGROUND

Clinical LC-MS/MS assays traditionally require that samples be run in batches with calibration curves in each batch. This approach is inefficient and presents a barrier to random access analysis. We developed an alternative approach called multipoint internal calibration (MPIC) that eliminated the need for batch-mode analysis.

METHODS

The new approach used 4 variants of 13C-labeled methotrexate (0.026-10.3 µM) as an internal calibration curve within each sample. One site carried out a comprehensive validation, which included an evaluation of interferences and matrix effects, lower limit of quantification (LLOQ), and 20-day precision. Three sites evaluated assay precision and linearity. MPIC was also compared with traditional LC-MS/MS and an immunoassay.

RESULTS

Recovery of spiked analyte was 93%-102%. The LLOQ was validated to be 0.017 µM. Total variability, determined in a 20-day experiment, was 11.5%CV. In a 5-day variability study performed at each site, total imprecision was 3.4 to 16.8%CV. Linearity was validated throughout the calibrator range (r2 > 0.995, slopes = 0.996-1.01). In comparing 40 samples run in each laboratory, the median interlaboratory imprecision was 6.55%CV. MPIC quantification was comparable to both traditional LC-MS/MS and immunoassay (r2 = 0.96-0.98, slopes = 1.04-1.06). Bland-Altman analysis of all comparisons showed biases rarely exceeding 20% when MTX concentrations were >0.4 µM.

CONCLUSION

The MPIC method for serum methotrexate quantification was validated in a multisite proof-of-concept study and represents a big step toward random-access LC-MS/MS analysis, which could change the paradigm of mass spectrometry in the clinical laboratory.

Quantification of Methotrexate in Human Serum and Plasma by Liquid Chromatography Tandem Mass Spectrometry

Mass spectrometry (MS) is a highly specific and sensitive technique that is used for the detection of many different analytes with diverse chemical characteristics. It has been adopted by clinical laboratories for the quantification of small molecules and, by extension, has been widely used for therapeutic drug monitoring. It is an attractive alternative to immunoassay methods, because it is not subject to the same interferences. A limitation of MS (relative to immunoassays) is the turnaround time. However, this can be addressed by workflow parallelization with other assays. Herein we describe a tandem LC-MS/MS method for the detection and quantification of methotrexate in human plasma with a lower limit of quantification of 0.01 μM and within-assay and between-assay coefficients of variation of less than 15%. This method lacks interference from high-abundance metabolites and utilizes kindred chromatography to improve turnaround time in the therapeutic drug monitoring laboratory.

A comprehensive study of umbilical cord blood cell developmental changes and reference ranges by gestation, gender and mode of delivery

OBJECTIVE

The purpose of this study was to determine the normal hematological values in cord blood during gestation, the impact of the type of delivery and differences in gender.

STUDY DESIGN

The database included 10 287 live births of 30-44 weeks gestation from cesarean or vaginal deliveries. Cord blood was collected into bags containing lyophilized heparin. Specimens were stored for 24 h or less and analyzed using the SysmexXE-2100. Data from cesarean births were used to evaluate developmental hematopoietic changes.

RESULT

Increases during maturation occurred in hemoglobin, hematocrit, red blood cell count, and decreases in mean corpuscular volume and mean corpuscular hemoglobin. The number of nucleated red blood cells per 100 white blood cells decreased but absolute counts remained constant. Quantitative counts of white blood cells, neutrophils, monocytes (MON), eosinophils and lymphocytes (LYMP) increased, but percentages of lymphocytes and monocytes decreased. Platelets increased from 30-35 weeks.

CONCLUSION

Reference ranges were established for cord blood. Erythroid and myeloid cells show developmental changes. Mode of delivery has a significant effect on hematologic values. Only a rare parameter showed differences based on gender. The cord blood complete blood cell count has the potential for providing relevant clinical information for managing neonatal patients.

Chromatic Influence of Value Resin Composites

Value resin composites used to replace enamel can induce a brightness decrease in stratified composite restoration techniques.