Improvement in the stability of serum samples stored in an automated refrigerated module.

OBJECTIVES: In clinical laboratories it is necessary to know for how long the analytes are stable in the samples with specific storage conditions. Our laboratory has implemented the new Aptio Automation System (AAS) (Siemens Healthcare Diagnostics) where the analyzed samples are stored in a refrigerated storage module (RSM) after being sealed. The aim of the study was to evaluate the stability of serum samples with the AAS and comparing the results with a previous study using a conventional refrigerated system. DESIGN AND METHODS: Serum samples from a total of 50 patients were collected and for each of them 27 biochemical analytes were analyzed. The samples were divided in 5 sets of 10 samples. Each set was re-analyzed at one of the following times: 24, 48, 72, 96 and 120h. Stability was evaluated according to the Total Limit of Change (TLC) criteria, which combine both analytical and biologic variation. RESULTS: A total of 26 out of 27 analytes were stable at the end of the study according to TLC criteria. Lactate dehydrogenase was not stable at 48h observing a decrease in its concentration until the end of the study. In the previous study (conventional storage system) 9 biochemical analytes were not stable with an increase of their levels due to the evaporation process. CONCLUSIONS: The RSM connected to the AAS improves the stability of serum samples. This system avoids the evaporation process due to the sealing of samples and allows better control of the samples during their storage.

Estabilidad de 27 magnitudes bioquímicas en muestras de suero conservadas en refrigeración / Stability of 27 biochemical parameters in serum samples stored in the refrigerator

Introducción: Para asegurar la fiabilidad de los resultados de las magnitudes bioquímicas en muestras conservadas durante varios días, se aconseja realizar estudios de estabilidad según las condiciones de conservación empleadas. Con el presente estudio queremos conocer los límites de estabilidad de 27 magnitudes bioquímicas bajo las condiciones de conservación utilizadas en nuestro laboratorio. Material y métodos: Se recogieron 20 muestras de suero en tubos con gel separador y se conservaron a 4 ◦C. Las magnitudes bioquímicas se midieron 2 veces al día, con un intervalo de 6 h, durante 5 días. El cambio de concentración de las magnitudes a cada uno de los tiempos (Xt) respecto al valor inicial (X0) se expresó como cambio porcentual (Xt%) = (Xt/X0)*100 y se calculó la media de dicho cambio (Xmt%). La estabilidad se evaluó según 3 criterios. Criterio metrológico según la variación analítica interdía (CVa), por el que la Xmt% no podría superar al cambio significativo mínimo (CSM = ±1,65*CVa). Criterio biológico basado en la variación biológica intraindividual (CVb), por el que la Xmt% no podría superar al cambio significativo deseable (CSD = ±0,5*CVb). Y criterio combinado de ambos, por el que la Xmt% no podría superar el límite de cambio total (LCT = ± √ (1,65*CVa)2 + (0,5*CVb)2). Resultados: Veinte magnitudes se consideraron no estables según CSM y 14 según CSD. Al final del estudio, 9 magnitudes se consideraron no estables según el criterio LCT. Conclusión: Los criterios CSM y CSD resultan demasiados restrictivos. La combinación de ambos se ajusta más a las necesidades de nuestro laboratorio. Cada laboratorio debería estudiar la estabilidad de sus muestras con sus propias condiciones de conservación (AU)

Introduction: To ensure the reliability of the results of biochemical parameters in samples stored for several days, it is advisable to carry out stability studies according to the storage conditions employed. The limits of stability of 27 biochemical parameters under the storage conditions used in our laboratory were determined. Material and method: Twenty samples were collected in serum tubes with gel separator and stored at 4◦C. The biochemical parameters were measured twice daily at an interval of 6 h for5 days. The change in the concentration of parameters at each of the times (Xt) compared to the initial value (X0) was expressed as a percentage change (Xt%) = (Xt/X0)*100 and the mean percentage change (Xmt%) was calculated. The stability was evaluated according to 3 criteria. Metrology criteria according to within-day analytical variation (CVa), by which Xmt % could not exceed the minimum significant change (MSC = ±1.65*CVa). Biological criteria based on intra-individual biological variation (CVb), by which Xmt % could not exceed the desirable significant change (DSC = ±0.5*CVb). And the criteria based on the combination of both, by which Xmt % could not exceed the total limit of change (TLC = ±√ (1.65*CVa) 2+ (0.5*CVb)2). Results: The 20 parameters were considered stable according to MSC and 14 were according to DSC. In the end, nine parameters were considered stable according to the TLC criteria. Conclusion: MSC and DSC criteria are too restrictive. The TLC criteria is better suited to the needs of our laboratory. Each laboratory should investigate the stability of samples with their own storage conditions (AU)

Analysis of peptidome profiling of serum from patients with early onset symptoms of ischemic stroke.

BACKGROUND: We sought to identify new serum biomarkers for the early diagnosis of ischemic stroke. METHODS: We collected 63 serum samples from patients with neurologic disease (45 patients with ischemic stroke, 18 patients with other neurologic disorders, and 56 healthy controls). Serum peptides were extracted using immobilized copper ion chromatography on a robotic platform. Mass spectra were acquired by matrix-assisted laser desorption/ionization-time of flight mass spectrometry using an Autoflex II spectrometer (Bruker Daltonics, Billerica, MA). Statistical analyses were performed with Clinprotools 2.2 software (Bruker Daltonics) and SPSS software (version 15.0; SPSS, Inc., Chicago, IL). RESULTS: No peptide biomarker or panel of peptide biomarkers was identified to differentiate between ischemic stroke and other neurologic disease, but ischemic stroke patients were differentiated from healthy controls with a single feature of the peptidome (sensitivity 88.6%; specificity 96.4%). CONCLUSIONS: Analysis of peptidome profiling of serum could be a useful tool in the search for early diagnostic biomarkers of ischemic stroke.