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There is a growing interest in the relevance of salivary cortisol and cortisone concentrations in stress-related research. To correctly attribute the magnitude of salivary cortisol and cortisone variation as an effect of a stressful event, a coherent understanding of the day-to-day intra-individual and inter-individual variability across the diurnal cycle of the two steroids is required. However, such information is currently lacking. This study aimed to overcome these existing limitations by performing an investigation of the biological variation (BV) of salivary cortisol and cortisone within one day and between five days using an LC-MS/MS method. Saliva samples were collected from 20 healthy volunteers immediately after waking up, at 8:00, 12:00, 15:00, 19:00 and 23:00 on each day over five days. All samples were analyzed in duplicate in one run. Nested ANOVA was used to calculate the sums of squares for analytical and biological components of variation. The within-subject BV of salivary cortisol and cortisone (CVI) ranged from a minimum of 29.3 and 19.0 % to a maximum of 56.5 and 49.1 %, respectively, while the between-subject biological variation (CVG) ranged from 29.7 and 29.0 % to 51.6 and 43.6 %. The reference change values (RCVs) ranged from 96 to 245 % for cortisol and from 55 to 194 % for cortisone. A medium index of individuality was observed for both compounds at all time points. This study provides updated BV estimates and RCVs for different times of day that can be used to assess the magnitude of change in biomarkers in future stress-related research. [ABSTRACT FROM AUTHOR]

Background and aims: The aim of this study was to investigate the possible preanalytical effect of incomplete filling of blood tubes on molecular biology assays. Materials and methods: The study population consisted of 13 healthy volunteers from whom 11 mL of whole blood was collected and then distributed in different volumes (1.5, 3.0, and 6.0 mL, respectively) into three 6.0 mL spray-dried and evacuated K2EDTA blood tubes. Automated RNA extraction was performed using the Maxwell® CSC RNA Blood Kit. DNA was extracted with a MagCorePlusII, with concomitant measurement of glyceralde-hyde-3-phosphate dehydrogenase (GAPDH) gene expression. The nucleic acid concentration was calculated using the NanoDrop 1000 spectrophotometer, and purity was assessed using A260/280 and A260/230 absorbance ratios. Results: The RNA concentration was higher in the tubes filled with 1.5 and 3.0 mL of blood than in the reference 6 mL filled tube. The RNA 260/280 and RNA 260/230 ratios did not differ significantly between the differently filled blood tubes. The DNA concentration remained constant in the differently filled tubes. Compared to the 6.0 mL reference filled tube, the 1.5 mL and 3.0 mL filled blood tubes displayed a lower DNA 260/280 nm ratio. The DNA 260/230 ratio did not differ significantly in any of the variously filled tubes. Compared to the 6.0 mL reference filled blood tube, the 1.5 mL and 3.0 mL filled blood tubes showed a significant increase in the GAPDHcycle threshold. Conclusions: Our results suggest that underfilling of K2EDTA blood tubes may be a modest but analytically significant source of bias in molecular biology testing. [ABSTRACT FROM AUTHOR]

The current study was designed to evaluate the analytical performance of the new Mindray highly sensitive cardiac troponin I (hs-cTnI) chemiluminescent immunoassay on Mindray CL-1200i, as a thorough validation of novel hs-cTnI methods is required before introduction into clinical practice. The evaluation of the analytical performance of this hs-cTnI immunoassay encompassed the calculation of the limit of blank (LOB), limit of detection (LOD), functional sensitivity, imprecision, linearity, 99th percentile upper reference limit (URL) and concordance with another previously validated hs-cTnI chemiluminescent immunoassay. The LOB and LOD were 0.32 and 0.35 ng/L, whilst the functional sensitivity (expressed as cTnI value with <10 % imprecision), was 0.35 ng/L. The linearity was excellent throughout a wide range of clinically measurable values (r=1.00 between 0.8 and 9,726.9 ng/mL). The intra-assay, inter-assay and total imprecision were 1.1–1.3 %, 5.5–8.1 % and 5.6–8.2 %, respectively. The 99th percentile URL calculated using residual plasma from 246 ostensibly healthy blood donors was 9.2 ng/L (4.3 ng/L in women vs. 12.3 ng/L in men). The Spearman's correlation between Mindray hs-cTnI and Access hs-TnI was 0.97, with mean bias of 7.2 % (95 % CI, 2.6–11.9 %). Although we failed to confirm the very optimistic analytical characteristics previously reported for this method, our evaluation of the novel Mindray hs-cTnI immunoassay on CL-1200i demonstrated that the overall performance is comparable to that of other commercially available hs-cTnI techniques, making it a viable alternative to other methods. [ABSTRACT FROM AUTHOR]