The Tianjin Chronic Low-grade Systemic Inflammation and Health (TCLSIH or TCLSIHealth) cohort study is a observational study was based on annual health examinations conducted in Tianjin Medical University General Hospital Health Management Center in Tianjin, China[13, 14], and focused on the relationship between chronic low-grade systemic inflammation and the health status. Participants, who had received health examinations, including medical examinations, such as blood tests, abdominal ultrasonography, anthropometric parameters (height and body weight) etc., and had completed questionnaires regarding their smoking and drinking habits and disease history over the course of January 2007 to December 2015, were recruited. Moreover, a detailed lifestyle questionnaire covering economic level, marital status, employment status, educational levels, physical activity, sleep habits, dietary habits, overall computer/mobile device usage times, television time, history of prior infections, and use of medicines as well as physical performance tests were administered to randomly selected subjects from this population since May 2013. The protocol of the study was approved by the Institutional Review Board of Tianjin Medical University, and written informed consent was obtained from each participant.
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A total of XXXX subjects participated in this study. However, participants who had a history of type 1 diabetes mellitus, or who missed information on hs-CRP, IMT or plaques were not included in the present study. After excluding those subjects, the final cross-sectional analysis population comprised 8000 participants including 6009 subjects with normal blood glucose metabolic status, 1428 subjects with pre-diabetes and 563 subjects with diabetes.
Assessment of T2DM
Fasting blood glucose (FBG) was measured by the glucose oxidase method. Blood samples for analysis of HbA1c were mixed with ethylenediaminetetraacetic acid (as an anticoagulant) before testing. HbA1c separation and quantification were performed using a high-performance liquid chromatography analyser (HLC-723 G8; Tosoh, Tokyo, Japan) with intra- and interassay coefficients of variation of <3%. To measure 2 h-blood glucose, subjects were given a standard 75-g glucose solution, and serum glucose was measured at 2 h after administration during the oral glucose tolerance test. In undiagnosed participants, type 2 diabetes mellitus (T2DM) was defined as HbA1c ≥ 6.5%, or FBG ≥ 7.0 mmol/L, or oral glucose tolerance test ≥ 11.1 mmol/L, or in a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random blood glucose ≥ 11.1 mmol/L. Prediabetes was defined as following: FBG from 5.6 mmol/L to 6.9 mmol/L, or 2-h PG in the 75-g OGTT from 7.8 mmol/L to 11.0 mmol/L, or HbA1c from 5.7% to 6.4%. Both above criteria were based on the American Diabetes Association 2014 criteria.
Assessment of hs-CRP
Levels of hs-CRP were measured by chemiluminescence immunoassay using CRP ia vitro diagnostic kits (snibe, Shenzhen, China), and expressed as ng/ml. The detection limit of the hs-CRP level was 0.13 ng/ml. The reference range of hs-CRP was 0~700 ng/ml. To investigate how the hs-CRP levels are related to the prevalence and incidence of increased IMT or plaques, we divided them into four categories according to the quartiles of participants.
Assessment of IMT and Plaques
One trained sonographer performed the carotid ultrasonography using echocolor-doppler ultrasonography (TOSHIBA, Xario660) equipped with a 7.5 MHz liner array to measure the carotid intima-media thickness (IMT). All participants were asked to remain in the supine position with the head extended and turned 45° to the contralateral side of the artery during the examination. Measurements were made of left and right common carotid artery and carotid sinus after the examination of a longitudinal section of 10 mm at a distance of 1 cm from the bifurcation. Carotid intima-media thickness was evaluated as the distance between the lumen-intima interface and the media-adventitia interface. Intima and media thicknesses were measured as the distance from the main edge of the first to the main edge of the second echogenic line. Increased IMT is characterized by the most left and right CCA (common carotid artery) intima-media thickness ≥ 1.0 mm or the most left and right carotid sinus intima-media thickness ≥ 1.2 mm. Plaque is characterized by the any point on the carotid artery intima-media thickness ≥ 1.5 mm. Each measurement was repeated 3 times. The average values of the right and left common carotid IMT was used for analysis.
Assessment of other variables
Blood pressure (BP) was measured twice from the right arm using an automatic device (Andon, Tianjin, China) after 5 min of rest in a seated position. The mean of these two measurements was taken as the BP value. Hypertension is defined as having a systolic BP (SBP) of ≥ 140 mmHg and/or a diastolic BP (DBP) of ≥ 90 mmHg, a history of hypertension, or the current use of antihypertensive medications. Blood samples for the analysis of lipids were collected in siliconized vacuum lastics tubes. Total cholesterol (TC) was measured by enzymatic methods, low-density lipoprotein (LDL) was measured by the polyvinyl sulfuric acid precipitation method, and high density lipoprotein (HDL) was measured by the chemical precipitation method using appropriate kits on a Cobas 8000 modular analyzer (Roche, Mannheim, Germany).
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Anthropometric parameters (height and body weight) were measured by experienced physicians. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters’ square (kg/m²). Waist circumference (WC) was measured at the umbilical level with participants standing and breathing normally.
Socio-demographic variables, including sex and age, were also assessed. A detailed personal and family history of physical illness and current medications was noted from ‘yes’ or ‘no’ responses to relevant questions. Information on alcohol and tobacco use was obtained from a questionnaire survey.
All statistical analyses were performed using the Statistical Analysis System 9.3 edition for Windows (SAS Institute, Inc., Cary, NC, USA). Measurement with a skewed distribution, serum TC, LDL, HDL and hs-CRP were normalized by logarithmic transformation before analysis and the geometric means (95% CI) are shown. For further analysis, the appearance of increased IMT or plaques was used as dependent variables, and the quartiles of hs-CRP levels were used as independent variables. For baseline characteristics analysis, continuous variables and proportional variables were compared with analysis of variance (ANOVA) and logistic regression analysis, respectively. For cross-sectional analysis, multivariate logistic regression analysis was performed to study the correlation of carotid IMT and serum hs-CRP levels. To assess the association of elevated serum hs-CRP with increased carotid IMT, an unadjusted logistic regression model and a fully-adjusted model, including age, sex, BMI, waist circumference, smoking status, drinking status, hypertension, hyperlipidemia, metabolic syndromes, and family history of cardiovascular disease, hypertension, hyperlipidemia, and diabetes were used. Odds ratios (ORs) (95% CI) were calculated. All tests were two-tailed and pï¼œ0.05 was defined as statistically significant.
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