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Sample analysis All serum samples were tested in duplicate on the Erenna SP ® sp platform by EMD Millipore Corporation, Hayward California. However, our CV SB A sb % was obtained from duplicates with median cMyC of 4.38 (2.75-5.97) ng/L, which is considerably lower than median cMyC found in patient with adjudicated diagnosis of acute coronary syndrome 237 (71-876) ng/L in the APACE cohort [[6]], and only ~5% of the 99th percentile (derived from patients without coronary artery disease) [[28]]. Analysis, confined to the initial presentation blood sample, showed that cMyC is at least as good as cardiac troponin measured with the leading assays in predicting the diagnosis of AMI, mortality and future cardiovascular events [[6]]. Keywords: biological variation; cardiac myosin-binding protein C; index of individuality; reference change value EN biological variation cardiac myosin-binding protein C index of individuality reference change value 576 583 8 03/11/22 20220301 NES 220301 Introduction Cardiac myosin-binding protein C (cMyC) is a novel biomarker of myocardial injury that was first identified in cardiac venous effluent approximately 10 years ago [[1]]. [Extracted from the article]

• Biological variation data is vital for analyzing and interpreting biomarker results. • Secretoneurin is a novel biomarker associated with arrhythmogenesis and mortality. • Secretoneurin shows low analytical and biological variation in healthy subjects. • Secretoneurin has low reference change values and index of individuality. • Secretoneurin delta values may reflect risk of cardiac arrhythmias and mortality. Secretoneurin is a novel prognostic biomarker that may predict mortality in heart failure and the occurrence of ventricular arrhythmias. This study reports the within subject variation (CV I), between subject variation (CV G), reference change values (RCV) and index of individuality (II) of secretoneurin. Thirty healthy volunteers were included. Non-fasting samples were obtained between 8 and 10 am once a week for ten weeks. Secretoneurin was analyzed in duplicate using ELISA. No outliers were present according to Burnett and Reeds' criteria. Simple linear regression did not identify significant trends. Variance homogeneity in the analytical variance and CV I were tested using Cochrane's and Bartlett's tests and four participants were excluded. Calculation of CV I , CV G and RCV were done on ln transformed data as described by Fokkema, the II was calculated using retransformed data. The median age of the participants was 36 years and 53% were female. Non-fasting glucose, eGFR (CKD-EPI) , cTnT and NT-proBNP concentrations were within the normal range. Median secretoneurin concentrations were 38 pmol/L (women) and 33 pmol/L (men), p-value < 0.001. CV I and CV G were 9.8% (CI 8.7% to 11.0%) and 20.0 (CI 15.4% to 28.0%), respectively. RCV were 38.7% (CI 35.5% to 42.7%) and −27.9 (CI −29.9 to −26.2) and the II were 0.60 (CI 0.42–0.78). No gender differences were present. Secretoneurin has a fairly low CV I , CV G , RCV and II, indicating that it could be suitable as a diagnostic or prognostic biomarker and that delta values in serial samplings may be preferable for identifying clinical changes. [ABSTRACT FROM AUTHOR]

• Analytical performance specifications for hs-cTn assays should be based clinical use. • Outcome studies suggest performance is sufficient for rapid identification of NSTEMI. • Biological variation may guide performance when hs-cTn are used for risk prediction. • Further improvement in analytical performance is likely to be clinically useful. Concurrent with the introduction of cardiac troponin measurements into the diagnostic definition of myocardial infarction (MI), clinicians and laboratory professionals signaled a clear clinical need for improved analytical quality. This was an important precipitant for developing high-sensitivity cardiac troponin (hs-cTn) assays, currently used in rapid algorithms guiding investigations of patients presenting to the emergency department with possible MI. The hs-cTn assays were also important for the detection and monitoring of low-grade chronic myocardial injury, a condition that has been linked to increased long-term risk of cardiovascular morbidity and mortality. This review summarizes the general recommendations for defining analytical performance specifications while providing relevant clinical situations related to analytical performance. Importantly, outcome studies suggest analytical quality performance for hs-cTn is sufficient for early discharge of patients investigated for possible MI. However, bias due to change in calibrators or reagents may significantly affect the percentage of patients discharged. Biological variation data is suitable for defining performance specifications when hs-cTn measurements are used for diagnosing and monitoring chronic myocardial injury. Further improvement in analytical performance for hs-cTn testing may result in even faster decision making in the emergency setting; while also identifying those with chronic injury at risk for an adverse cardiac event. [ABSTRACT FROM AUTHOR]

Background: Middle- and long-term biological variation data for hematological parameters have been reported in the literature. Within-day 24-h variability profiles for hematological parameters are currently lacking. However, comprehensive hour-to-hour variability data are critical to detect diurnal cyclical rhythms, and to take into account the 'time of sample collection' as a possible determinant of natural fluctuation. In this study, we assessed 24-h variation profiles for 20 hematological parameters. Methods: Blood samples were collected under standardized conditions from 24 subjects every hour for 24 h. At each measurement, 20 hematological parameters were determined in duplicate. Analytical variation (CVA), within-subject biological variation (CVI), between-subject biological variation (CVG), index of individuality (II), and reference change values (RCVs) were calculated. For the parameters with a diurnal rhythm, hour-to-hour RCVs were determined. Results: All parameters showed higher CVG than CVI. Highest CVG was found for eosinophils (46.6%; 95% CI, 34.9%-70.1%) and the lowest value was mean corpuscular hemoglobin concentration (MCHC) (3.2%; 95% CI, 2.4%-4.8%). CVI varied from 0.4% (95% CI, 0.32%-0.42%) to 20.9% (95% CI, 19.4%-22.6%) for red cell distribution width (RDW) and eosinophils, respectively. Six hematological parameters showed a diurnal rhythm. Conclusions: We present complete 24-h variability profiles for 20 hematological parameters. Hour-to-hour reference changes values may help to better discriminate between random fluctuations and true changes in parameters with rhythmic diurnal oscillations. [ABSTRACT FROM AUTHOR]