Who is in the cohort?
This study was conducted in 13 regions of 5 western provinces (Xinjiang: Moyu county, Yining city, Urumchi city; Gansu: Wuwei city, Tianshui city, Gannan city, Baiying city; Qinghai: Xining city; Ningxia: Qingtongxia city, Pingluo city; Shaanxi: Zhenba county, Baoji city, Xi’an city.) of Northwest China, with the regions chosen according to local disease patterns, exposures to certain risk factors, the distribution of ethnic groups, population size and stability, quality of death and disease registries and local commitment and capacity (Figure 1). This study was designed to include 100,000 participants and was managed by each provincial project group (Xinjiang: Xinjiang Medical University; Gansu: Gansu University of Chinese Medicine; Qinghai: Qinghai Center of Disease Prevention and Control; Ningxia: Ningxia Medical University; Shaanxi: Xi’an Jiaotong University), with each group responsible for the baseline survey measurements, including the questionnaire interview, the blood sample collection and storage and further follow-up work. The Shaanxi project team worked as the general manager in charge of the operation of the project. The baseline survey was conducted between June 2018 and May 2019.
A baseline survey was conducted via face-to-face interviews and clinic visits, with the assistance from local health staffs. The samples in the cohort consisted of permanent residents (aged 35-74 years), and any individuals attending the baseline survey who were slightly outside of the target age range were not turned away from the study, in order to encourage participation. In addition, we excluded the participants who had severe mental diseases or disabilities that hindered their ability to communicate in order to obtain accurate data. All the participants were asked to bring their national identity cards in order to exclude individuals who were not local permanent residents because these individuals were unavailable to be followed. All of the participants signed the informed written consents, which allowed us to access their medical records and their long-term storage supplies of blood samples for solely medical research purposes.
How often will participants be followed?
The National Death Surveillance System (NDSS), Chronic Disease Registries (CDR), The National Central Cancer Registry (NCCR) and National Health Insurance Claim Datasets (NHICD) enabled us to conduct passive follow-ups by periodic linking (every 6 months) of the baseline survey data to the NDSS, CDR, NCCR and NHICD. The NDSS and CDR are both based on the China’s Disease surveillance points system. The causes of death of the study participants were regularly monitored through the use of official death certificates that were reported to the regional Center for Disease Control and Prevention (CDC), wherein the NDSS was based; additionally, the NDSS was available in all 13 study regions. Information on chronic diseases (diabetes, hypertension, heart failure, stroke and cancer, among other diseases) is currently being collected through linkage with the NCCR, CDR and NHICD. The new national health insurance claim datasets are now fully established in all 13 study regions, and future incidences of chronic disease and the hospitalization information will be primarily extracted from the NHICD. Because the quality of the data from the NCCR and CDR is insufficient, the NCCR and CDR were not primary data sources but were complementary sources for the passive follow-up. The unique national identity card and health insurance card numbers were used as key variables to link the baseline data to the NDSS, CDR and NHICD. The diagnoses of these diseases are based on well-accepted international standards. The causes of death are coded according to the 10th version of the international statistical classification of diseases (ICD-10)(21). Approximately 10% of the participants will be actively followed every 3 years via face-to-face interviews, in order to estimate the changes of lifestyle and exposure factors and to identify the participants who have permanently moved out of the study regions, as well as to minimize the under-reporting of vital status and death data. In addition, biological specimens, including blood, saliva and stool samples, are planned to be collected. The rate of loss of individuals to the follow-up will aim to be less than 10%.
What has been measured?
In general, all the participants were asked to fast overnight for at least 8 hours before arriving at the local clinical centre, after which questionnaire surveys, physical examinations, laboratory tests and biological sample collections were conducted. A tablet computer with a self-developed application (the CNC App) was used to collect the questionnaire information, of which the main content referred to the study of the China Kadoorie Biobank as a reference(22), with the information being collected via face-to-face interviews that were performed by well-trained technicians. In addition, blood samples and anthropometric measurements were performed by professional physicians or nurses. The entire visiting procedure, including the electronic questionnaire interview, medical examinations and sample collections, typically took 60-75 min for each participant to complete.
The face-to-face questionnaire interview was conducted to collect baseline information about the participants, including demographic and social-economic characteristics (sex, date of birth, ethnic group, education, marital status, occupation and income, among other factors), lifestyle factors (tea and coffee drinking habits, alcohol consumption, smoking history and dietary status, among other factors), environmental exposures (passive smoking and indoor air pollution, among other factors), medical history, mental health status and reproductive history (Table 1). To ensure the quality of the data from the questionnaire survey, reviewers were trained on the unifying process and the mode of query.
The medical examinations were primarily conducted by using the resources and personnel at the local clinical centres. Standardized training for the doctors, nurses and technicians was implemented before the investigation. The items of the medical examinations for all of the participants included height, weight, waist circumference, heart rate, body fat percentage (BFP), visceral fat index (VFI), basal metabolic rate (BMR), bone mass, muscle mass, total body water (TBW) and resting blood pressure. The project group (the provincial CDC or a local medical college) had the primary responsibility of quality control, as guided by the alternative methods of the study. The values of the medical examinations were estimated to have optimal consistency among the devices that were used in 5 provinces. In addition, other items (lung function, blood and urine routine examinations, liver and kidney function tests, glycosylated haemoglobin measurements and B-ultrasonic examinations, among other tests) have been selectively tested in a portion of the participants (approximately 40%).
After at least 8 hours of fasting, 10 ml venous blood samples were collected from all of the participants at the time of the baseline survey. The venous blood was transferred into one 5.0 mL ethylenediamine tetra acetic acid dipotassium (EDTA K2) anticoagulation tube and one 5.0 mL vacuum tube without anticoagulation. Plasma, serum and buffy coat samples were separated from the whole blood via centrifugation for 10 min at the relative centrifugal force of 3000 g at 4 ℃. Due to limited funds, partial serum samples (approximately 40%) were forwarded to measure various biochemical indexes, including fasting blood glucose, blood lipids, kidney function and high-sensitivity C-reactive protein (hsCRP) tests, among other indexes, within 2 hours.
During the baseline survey period, five provincial biobanks were established, which were responsible for the storage and management of the biological samples of the CNC. All of the blood samples were stored in a -20 °C freezer before being transferred to be stored at -80 °C in cryogenic refrigerators that were located in each provincial biobank in the local CDC, medical college or affiliated hospital of the university via cold chain. To ensure the safety of the biological samples, a portion of the blood samples (including 5 ml plasma and 5 ml whole blood of the participants that were stored in four other provincial Biobanks [except for the Xi’an biobank]) were required to be transferred to the Xi’an biobanks in Shaanxi province as a back-up storage. Due to the long distance between the Shaanxi province and the other 4 provincial sites (especially Xinjiang), the quality control of each shipment was a key issue that had to be specifically considered. To prevent any blood sample from thawing during the shipment from each site to the Xi’an biobank, an electronic thermometer was placed in each sample’s dry ice box, in order to dynamically monitor the temperature; additionally, the temperature of each of the samples was maintained at a range of -60--80 °C in the old chain trucks.
A computer-based scanning and packing system for the biological samples was developed, in order to assist in blood sample entry into the cryogenic refrigerators in the biobank. Moreover, quality control requirements were strictly followed throughout the process of blood sample collection, shipment and storage, such as checking the identity of the sample and the participant ID, regulating the storage time and standardizing the volume of the samples and the temperature conditions of the samples on site, in order to ensure high-quality blood samples. In total, approximately 0.88 million blood samples (including plasma, serum, buffy coat and whole blood samples) have been stored in the CNC biobank.