Prevalence, perception and factors associated with diabetes mellitus among the adult population in central Vietnam: a population-based, cross-sectional seroepidemiological survey

We conducted a cross-sectional, population-based seroprevalence survey in Khánh Hòa Province, which is in the south-central coastal region of Vietnam, in December 2014 using three-stage cluster sampling. This province covers an area of 5217.7 km² and had a population of nearly 1.2 million as of 2014 [12]. The primary economic sectors of this province are industry, construction, and services-tourism [13], and according to official provincial documents 56% of the communities are rural.

We targeted adult residents of Khánh Hòa Province aged 20–70 years; pregnant women or those who had given birth within the previous 3 months were excluded in order to avoid misclassification due to the likelihood of unstable glycosylated hemoglobin (HbA1c) levels caused by gestational DM.

The required sample size was 426.8 as determined using the equation n = Z ² × p(1-p)Deff/(e ² × RR) from the sample size calculator [14] provided by the World Health Organization (WHO) STEPwise approach to noncommunicable disease risk factor surveillance (STEPS) [15] with a level of confidence (Z) of 1.96 for a 95% CI, an estimated prevalence of DM (p) of 0.05, a design effect (Deff) of 2.0, a margin of error (e) of 0.03, and an expected response rate (RR) of 0.95. A total of 480 subjects were randomly selected from the population and residents lists from the province using probability proportional to size (PPS) sampling as follows: 10 out of 137 wards/communes, three villages from each ward/commune, and 16 adult inhabitants from each village.

Blood was collected after at least 8 h of fasting, as instructed in invitation letters to the participants. Those who met any of the following criteria were consider to have DM [16]: 1) elevated HbA1c level ≥ 6.5%; 2) elevated fasting plasma glucose (FPG) level ≥ 7.0 mmol/L (126 mg/dL) or random elevated plasma glucose level ≥ 11.1 mmol/L (200 mg/dL); or 3) history of treatment for DM (lifestyle guidance including diet or exercise advice, oral medication, or insulin). Those with a marked discrepancy between HbA1c and FPG levels without factors related with DM who were strongly suspected as having hemoglobinopathy were excluded based on clinical grounds.

Residential areas were categorized as either rural or urban based on government classifications. Monthly household income was converted according to the rates in December 2014 (1,000,000 VND = 47.3 USD) [17]. BMI was calculated as body weight (kg) divided by the square of height (m²), and then classified as follows: overweight as ≥25 kg/m² and <30 kg/m², and obese as ≥30 kg/m² [18]. Hypertension was defined as elevated blood pressure (BP), with systolic BP ≥ 140 mmHg and/or diastolic BP ≥ 90 mmHg [19]. Hyperlipidemia was determined as the existence of any of the following factors: 1) high total cholesterol (TC) level as ≥6.2 mmol/L (240 mg/dL) from a multi-country study [20]; 2) low high-density lipoprotein cholesterol (HDL-C) level as <1.0 mmol/L (40 mg/dL); and 3) high triglyceride level as ≥2.3 mmol/L (200 mg/dL) based on the definition of the laboratory institute. Metabolic syndrome was defined as the existence of any three of the following five factors: 1) waist circumference ≥ 90 cm for males or ≥80 cm for females in the Asian population; 2) triglyceride level ≥ 1.7 mmol/L (150 mg/dL); 3) HDL-C level < 1.0 mmol/L (40 mg/dL) for males and <1.3 mmol/L (50 mg/dL) for females; 4) systolic BP ≥ 130 mmHg and/or diastolic BP ≥ 85 mmHg; and 5) FPG level ≥ 5.6 mmol/L (100 mg/dL) or drug treatment for elevated glucose level [21].

We also explored the perception of DM using structured questionnaires by asking whether they had heard of it or not, moreover whether they understood what DM was if they had heard of it before. Likewise we asked their recognition of current and/or past history of high blood sugar values or DM to let them choose one among yes, no, or unknown. These answers were self-reported and their actual knowledge regarding DM were not verified, while the status of DM in each subject were determined in this study the results of which were tabulated.

The survey process and procedures were carried out in reference to STEPS [15].

Two survey teams composed of researchers or medical and paramedical officers from the Nha Trang Pasteur Institute (IPN) and the Endocrinology Center of Khánh Hòa Provincial Health Service were employed, with three supervisors and nine surveyors deployed to each team. A 2-day training session on the survey process, including questionnaire pretesting, was conducted prior to the survey. General information regarding the survey was sent in an announcement letter to the participants, accompanied by instructions to fast for at least 8 h before blood tests.

The survey was conducted at 10 commune health centers (CHCs) over a 6-day period. Participants living in the three villages in each catchment area were invited to their respective CHCs at dawn, and the survey process was conducted throughout the early morning. Laboratory tests and data entry were then carried out in the afternoon every day at the IPN.

After obtaining written informed consent, interviews were conducted using a structured questionnaire, BP and anthropometric measurements were taken, and blood sampling was performed. The structured questionnaire was composed of closed questions with regard to sociodemographic profiles, lifestyle activities, history and perception of DM, and time of last food intake to assure proper fasting prior to testing for FPG. Anthropometric measurements included height, weight, and waist and hip circumference. Venous blood samples (5 mL) were drawn from each participant by experienced nurses or lab technicians and collected into ethylenediaminetetraacetic acid (EDTA) or plain blood tubes. The EDTA tubes were stored in special blood containers (CubeCooler, Forte Grow Medical Co., Ltd., Tochigi, Japan) at 0–5 °C. Blood in plain tubes was centrifuged at 3000 rpm for 15 min within 30 min after sampling, and supernatant serum was then transferred into microtubes stored on ice to prevent degradation of glucose levels. Finally, all questionnaires were checked by supervisors to ensure that all required answers were appropriately marked.

Blood samples processed in each CHC were transported to the IPN within about 6 h after sampling and tested for HbA1c, glucose, TC, HDL-C and triglycerides. HbA1c was quantified using high-performance liquid chromatography (HPLC; HLC-723 G8; TOSOH, Tokyo, Japan). Glucose, TC, HDL-C and triglycerides were measured in serum. The type of DM among those determined to have DM in this study were not differentiated by further detailed investigation.

All data were validated using double-entry methods and data cleaning, and then analyzed using STATA IC 11 (Stata Corp., College Station, TX, USA) in accordance with the case definitions as indicated above. The characteristics of the enrolled participants were tabulated, and the proportions of those who had DM were calculated using point estimation with 95%CIs. Odds ratios (ORs) and adjusted ORs (aORs) of having DM (95%CI) were estimated in univariate and multivariate analysis using a logistic regression model. The association was regarded as being statistically significant when the 95%CI did not contain the value 1.0.

This study was approved by the Institutional Review Boards of the National Center for Global Health and Medicine (NCGM-G-001644-00) in Japan and the IPN. In addition, the protocol and operation of this survey were authorized by the Khánh Hòa Province People’s Committee and the Provincial Health Department. Informed consent was obtained in writing or by thumbprint from all participants. All personal information was kept confidential. The notice of results included advice for medical consultations at CHCs or other health facilities if any abnormal findings were found, and the CHCs involved in this study were expected to follow-up the participants accordingly.

As shown in Table 1, 376 of the 480 participants were finally enrolled (response rate: 78.3%). The reasons for failed enrollment included moving out of the study area or refusing to participate. Females accounted for 59.0% of the participants, and the mean age ± standard deviation was 42.9 ± 12.7 years. Rural residents accounted for 61.4% of the participants and tended to be younger than urban residents. More than half of the males were manual workers, with more than 60% engaging in heavy physical activity. Regarding females, three in 10 were homemakers or unemployed, with more than 60% engaging in light activity. Nearly 80% of males were current or past smokers and 13% drank alcohol more than 4 days per week. By contrast, only a small proportion of females engaged in such behaviors. Among the participants, 14.3% and 18.9% of males and females, respectively, were classified as overweight/obese according to BMI, 37.7% and 22.1% as having hypertension, and 36.4% and 11.7% as having metabolic syndrome.

Among the 376 participants, 27 were identified as having DM, which accounted for 7.2% (95%CI: 4.6–9.8) of the sample, with 7.1% (3.0–11.3) for males and 7.2% (3.8–10.6) for females. These 27 cases met the criteria for DM, as defined above, as follows: 1) elevated HbA1c level (18/376, 4.8%); 2) elevated FPG level or random elevated plasma glucose level (14/376, 4.0%); and 3) presence of history of treatment for DM (10/376, 2.7%). One case with suspected hemoglobinopathy with extremely high HbA1c level (14.1%) and normal FPG level (4.9 mmol/L) was excluded.

Multivariate analysis identified that those aged 60–70 years (aOR: 8.7; 95%CI: 1.4–56.0) and those being classified as obese according to BMI (aOR: 10.2; 95%CI: 2.2–50.2) were at a higher risk for DM than those aged 30–39 years and those classified as having low or normal BMI, respectively (Table 2).

More than two-thirds (254/376, 67.6%) of the participants either did not understand or had never heard of DM, and less than half of the DM cases (12/27, 44%) had been aware of or reported their history of DM (Table 3).