Assessment of serum total 25-hydroxyvitamin D assays for Vitamin D External Quality Assessment Scheme (DEQAS) materials distributed at ambient and frozen conditions.

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes human serum samples four times per year to over 1000 participants worldwide for the determination of total serum 25-hydroxyvitamin D [25(OH)D)]. These samples are stored at -40 °C prior to distribution and the participants are instructed to store the samples frozen at -20 °C or lower after receipt; however, the samples are shipped to participants at ambient conditions (i.e., no temperature control). To address the question of whether shipment at ambient conditions is sufficient for reliable performance of various 25(OH)D assays, the equivalence of DEQAS human serum samples shipped under frozen and ambient conditions was assessed. As part of a Vitamin D Standardization Program (VDSP) commutability study, two sets of the same nine DEQAS samples were shipped to participants at ambient temperature and frozen on dry ice. Twenty-eight laboratories participated in this study and provided 34 sets of results for the measurement of 25(OH)D using 20 ligand binding assays and 14 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. Equivalence of the assay response for the frozen versus ambient DEQAS samples for each assay was evaluated using multi-level modeling, paired t-tests including a false discovery rate (FDR) approach, and ordinary least squares linear regression analysis of frozen versus ambient results. Using the paired t-test and confirmed by FDR testing, differences in the results for the ambient and frozen samples were found to be statistically significant at p < 0.05 for four assays (DiaSorin, DIAsource, Siemens, and SNIBE prototype). For all 14 LC-MS/MS assays, the differences in the results for the ambient- and frozen-shipped samples were not found to be significant at p < 0.05 indicating that these analytes were stable during shipment at ambient conditions. Even though assay results have been shown to vary considerably among different 25(OH)D assays in other studies, the results of this study also indicate that sample handling/transport conditions may influence 25(OH)D assay response for several assays.

An international assessment of the metrological equivalence of higher-order measurement services for creatinine in serum.

The Consultative committee for amount of substance-metrology in chemistry (CCQM)-K80 Key Comparison directly assessed the equivalence of many of the world's higher-order value-assigned materials (HOVAMs) for creatinine in human serum. This 2009 international study compared the certified values and uncertainties of the materials using measurements made under repeatability conditions. The study evaluated 17 materials submitted by 6 national metrology institutes (NMIs). The creatinine quantity in these materials ranged from 3 mg/kg to 57 mg/kg (about 0.3 mg/dL to 6 mg/dL or 30 nmol/L to 500 nmol/L). All materials were stored and prepared according the specifications provided by the participating NMIs. Samples were processed and analyzed under repeatability conditions by one analyst using isotope-dilution liquid chromatography-mass spectrometry in two measurement campaigns. The certified values and repeatability measurements were compared using uncertainty-weighted generalized distance regression. The instrumental repeatability relative standard deviation was 1.2%. The measurement design required assessment of within-unit and between-campaign variability in addition to measurement repeatability. At a 95% level of confidence, the certified values for all 17 materials agreed to within their assigned uncertainties. CCQM-K80 demonstrated the metrological equivalence of the currently available HOVAMs for creatinine in human serum and of the creatinine measurement services provided by the participating NMIs.

Multiplex_QA: an exploratory quality assessment tool for multiplexed electrophoretic assays.

Multiplex_QA is a data analysis tool for visualizing short- and long-term changes in the performance of multiplexed electrophoretic assays, particularly the commercial short tandem repeat (STR) kits used by the human forensic identity community. A number of quality metrics are calculated from the signal collected for the internal size standard included in nearly all multiplex assays. These quality metrics are related to the signal intensity, symmetry, retention, resolution, and noise of data collected by capillary electrophoresis systems. Interlocking graphical displays enable the identification of changes in the quality metrics with time, evaluation of relationships among the metrics, and detailed examination of electropherographic features of particularly interesting analyses. While primarily intended for exploring which metrics are most useful for documenting data quality, the current version of the tool is sufficiently robust for use by forensic scientists with an interest in data analysis and access to a fast desktop computer.