PropertyValue
is nif:broaderContext of
nif:broaderContext
is schema:hasPart of
schema:isPartOf
nif:isString
  • The CoLaus Study was approved by the Institutional Ethics Committee of the University of Lausanne (decision 19 February 2003, protocol number 16/03). Written informed consent was obtained from all participants. The CoLaus Study is a cross-sectional study aimed at assessing the prevalence of CVD risk factors as the molecular determinants of CVD in the Caucasian population of Lausanne, Switzerland, a town of 117,161 inhabitants, of which 79,420 are of Swiss nationality. The sampling procedure of the CoLaus Study has previously been described [9]. Recruitment began in June 2003 and ended in May 2006. Participation rate was 41%. All participants attended the outpatient clinic of the University Hospital of Lausanne in the morning after an overnight fast. Data were collected by trained field interviewers in a single visit lasting about 60 min. No information regarding revenues or social deprivation was collected. Participants were classified as never, current, or former smokers. A participant was considered as physically active if he/she reported practicing at least 2 hours of leisure-time physical activity per week. Body weight and height were measured with participants standing without shoes in light indoor clothes. Body weight was measured in kilograms to the nearest 100 g using a Seca® scale, regularly calibrated. Height was measured to the nearest 5 mm using a Seca® height gauge. Overweight was defined as a BMI ≥25 and <30 kg.m−2; obesity was defined as a BMI ≥30 kg.m−2. Venous blood samples (50 mL) were drawn in the fasting state and allowed to clot. Serum was preferred to plasma as it has been shown that different anticoagulants may affect absolute cytokine levels differently [10], [11]. High sensitive CRP (hs-CRP) was assessed by immunoassay and latex HS (IMMULITE 1000–High, Diagnostic Products Corporation, LA, CA, USA) with maximum intra- and interbatch coefficients of variation of 1.3% and 4.6%, respectively. Serum samples were kept at −80°C before assessment of IL-1β, IL-6, and TNF-α and sent in dry ice to the laboratory. Levels of these cytokines were measured using a multiplexed particle-based flow cytometric cytokine assay [12]. This methodology yields cytokine concentrations which correlate well with those obtained by other methods such as ELISA [13] (for a review, see [14]). Milliplex kits were purchased from Millipore (Zug, Switzerland). The procedures closely followed the manufacturer's instructions. The analysis was conducted using a conventional flow cytometer (FC500 MPL, BeckmanCoulter, Nyon, Switzerland). Lower limits of detection (LOD) for IL-1β, IL-6 and TNF-α were 0.2 pg/ml. A good agreement between signal and cytokine was found within the assay range (R2≥0.99). Intra and inter-assay coefficients of variation were respectively 15% and 16.7% for IL-1β, 16.9% and 16.1% for IL-6 and 12.5% and 13.5% for TNF-α. For quality control, repeated measurements were conducted in 80 subjects randomly drawn from the initial sample. Statistical analysis was conducted using SAS v.9.2 (SAS Inc, Cary, NC, USA). Reproducibility between the first and the second measurement was assessed by Spearman nonparametric correlation, intraclass correlation coefficients, Lin's concordance correlation and Bland-Altman plots. Lin's concordance correlation measures how well a new set of observations reproduces an original set and has been reported to be more appropriate than other indices for measuring agreement when the variable of interest is continuous. Quantitative variables (apart from inflammatory biomarkers) were expressed as mean ± standard deviation and qualitative variables as number of participants and (percentage). Biomarkers were presented as median and (interquartile range) of measured values, percentage of values below LOD and percentage of values within each quartile. Undetectable values were included in the first quartile. Between groups comparisons were performed using Student t-test or Kruskall-Wallis nonparametric test for quantitative and chi-square test for qualitative variables. The relationships between biomarker values (excluding undetectable ones) and selected quantitative variables (i.e. age and BMI) were assessed using Spearman's nonparametric correlation; similar analyses were performed replacing values below LOD by a) half the limit of detection [15] and b) multiple imputation of missing data using a Markov Chain Monte Carlo method [16] and five imputation sets. Multivariate analysis was conducted by multivariate linear regression using log-transformed cytokine values as dependent variable, a method used elsewhere [4]. Two models were applied: the first using only measured data, the second replacing values below LOD by half the limit of detection. The results were expressed as slope and (standard error). We also used multivariate logistic regression to assess the likelihood of being in the topmost quartile compared to the other three quartiles as well as being in the topmost vs. the lowest quartile of cytokine distribution. Results of the logistic analysis were presented as Odds-ratio (OR) and (95% confidence interval). Statistical significance was considered for p<0.05.
rdf:type