Does the Disparity Patterning Differ between Diagnosed and Undiagnosed Hypertension among Adults? Evidence from Indonesia

Background: Healthcare systems in many low- and middle-income countries (LMICs) are not yet designed to tackle the high and increasing burden of non-communicable diseases (NCDs), including hypertension. As a result, a large proportion of people with disease or risk factors are undiagnosed. Policymakers need to understand the disparity better to act. However, previous analyses on the disparity in undiagnosed hypertension, especially from LMICs, are lacking. Our study assessed the geographic and socioeconomic disparity in undiagnosed hypertension and compared it with diagnosed hypertension. Methods: We used the Basic Health Survey (Riskesdas) 2018 and performed geospatial and quantitative analyses across 514 districts in Indonesia. Dependent variables included diagnosed and undiagnosed hypertension among adults (18+ years) and by gender. Results: A high prevalence of undiagnosed hypertension at 76.3% was found, with different patterns of disparity observed between diagnosed and undiagnosed hypertension. Diagnosed hypertension was 1.87 times higher in females compared with males, while undiagnosed hypertension rates were similar between genders. Urban areas had up to 22.6% higher rates of diagnosed hypertension, while undiagnosed hypertension was 11.4% more prevalent among females in rural areas. Districts with higher education rates had up to 25% higher diagnosed hypertension rates, while districts with lower education rates had 6% higher rates of undiagnosed hypertension among females. The most developed regions had up to 76% and 40% higher prevalence of both diagnosed and undiagnosed hypertension compared with the least developed regions. Conclusion: The disparity patterning differs between diagnosed and undiagnosed hypertension among adults in Indonesia. This highlights the need for effective measures, including healthcare system reforms to tackle NCDs in LMICs.


Background
Hypertension, or high blood pressure, is linked with increased heart, brain, and kidney disease risks [1]. Globally, about 1.3 billion adults aged 30 years and over had hypertension in 2021. Most of those with hypertension (over 60%) are in low-and middle-income countries (LMICs) [1]. Moreover, data also showed that less than half (42%) of those with hypertension were diagnosed and treated [1]. In Indonesia, hypertension is also high and increasing. Analyses from the nationally representative survey (RISKESDAS) showed that hypertension prevalence among adults 18 years and over was 34.1% in 2018, which increased considerably from 25.8% in 2013 [2]. Moreover, a study of the Indonesian Family Life Survey 2016 found that the prevalence of hypertension among adults 40 years and over was 47.8%, of which almost 70% were undiagnosed [3].
The current literature provides some evidence of social determinants of cardiovascular diseases and risk factors including hypertension [4]. A comprehensive literature review and meta-analysis in 2014 found that income level was positively associated with hypertension, but education level was not. The study also found geographic variation in the association between education and hypertension, showing an inverse association in the East Asian region and a positive one in the South Asian region [5]. A study in 2017 using the South Korean National Health and Nutrition Examination Survey (NHNES) found sexual variation in the association between education and undiagnosed hypertension, showing an inverse association among women but not among men [6]. Recent analyses (2019-2021) of the Demographic & Health Survey data in Peru, Bangladesh, and Nepal also found that adults from lower socioeconomic and educational backgrounds had higher odds of undiagnosed hypertension [7][8][9][10]. Another study in 2016 showed that being in a deprived neighborhood increased the influence of individual socioeconomic status on mortality among newly diagnosed hypertension patients in South Korea [11]. Similarly, a study in Peru found that adult males living in the more remote and deprived areas (e.g., coasts and mountains) had a higher prevalence of undiagnosed hypertension [7]. A study in the United States showed that rural areas were most vulnerable to adverse chronic health outcomes and found a positive association between social vulnerability index and cardiometabolic indicators including hypertension [12].
To achieve the SDG target 3.4.1 to reduce premature mortality from NCDs by onethird by 2030, efforts need to aim at reducing the disparity in diagnosed and undiagnosed hypertension [1]. However, the current literature on such disparity is limited in three ways. First, while most of the current literature used data at the individual level (e.g., national surveys) [3,[5][6][7][8][9][10], studies that employed data at the local level (such as districts) are lacking. Such evidence is also crucial, especially in countries with more local decision space, such as Indonesia. Second, because of the better availability of local level data, current geographic analyses are mainly from high-income countries such as the United States and South Korea [11,13,14]. Such analyses from LMICs (e.g., China, Thailand, and Peru) are limited to the urban/rural and provincial levels [15][16][17]. Third, previous studies focused on overall hypertension and lacked disaggregation between diagnosed and undiagnosed hypertension. Effective health system reforms and population-based interventions may be needed to reduce the undiagnosed population [18]. Our study aimed to assess the disparity (geographic and socioeconomic) in diagnosed and undiagnosed adult hypertension across over 500 Indonesian districts.

Study Design
This is a cross-sectional study comparing the disparity in diagnosed and undiagnosed hypertension among adults. We analyzed geographic and socioeconomic disparities across 514 districts within 34 provinces in Indonesia. We took advantage of the 2018 Basic Health Survey (Riskesdas) data that were representative at the district level for diagnosed and undiagnosed hypertension. The survey conducted interviews and physical examinations of about 300,000 households from a two-stage sampling procedure. The sampling first randomly selected 30,000 census blocks (out of a total of over 700,000 in Indonesia). Within each block, 10 households were systematically selected, which resulted in 624.563 adults (18+ years). The mean ages (standard deviation) were 41.0 (15.5) years, 40.8 (15.3) years, and 41.3 (15.7) years for all adults, males, and females, respectively [2].

Independent Variables
The main independent variables included geographic and socioeconomic indicators at the district level. The variables used in our analyses were region, urbanicity, income level, and education level. This information was taken from the World Bank. The regional variable includes five regions: Sumatera, Java (including Bali), Kalimantan, Sulawesi, and Papua (including Nusa Tenggara and Maluku). Generally, the eastern parts of the country are the least developed [19][20][21]. Appendix A provides the map reference. The urbanicity variable shows cities as urban and regencies as rural areas. For the income variable, we used the poverty rates information at the district level, which we then grouped into quintiles. For the education variable, we used net enrollment ratios of senior secondary information, which we grouped into quintiles as well [22][23][24].

Dependent Variables
There were six dependent variables used in our analysis, including diagnosed adults, diagnosed males, diagnosed females, undiagnosed adults, undiagnosed males, and undiagnosed females. Diagnosed hypertension was a binary variable with a value of 1 if one reported ever being told by a doctor that they have high blood pressure and 0 if otherwise. We defined undiagnosed hypertension as not diagnosed but meeting the criteria for hypertension based on the blood pressure measurement (i.e., either systolic blood pressure of at least 140 mmHg, diastolic blood pressure of at least 90 mmHg, or both) [25].

Data Analysis
We performed both geospatial analyses and multivariable regression analyses in this paper. In conducting the geospatial analyses, we grouped each dependent variable for 34 provinces and 514 districts by quintile. In conducting the regressions, we employed ordinary least squares and examined the relationship between independent and dependent variables. We compared the regional variations between the western and eastern parts of the country, and the income/education variations between the poorest/least educated and wealthiest/most educated. The geospatial analyses were conducted in ArcMap 10 and the statistical analyses were performed in STATA 15, using 5% as statistically significant.  Table 1 show results at the provincial level. Figure 1 compares diagnosed hypertension (panels a-c) and undiagnosed hypertension (panels d-f) by quintile. At the provincial level, diagnosed hypertension among all adults ranged from 4.4% to 13.2%; males from 3.7% to 9.5%; and females from 5.2% to 17.0%. At that level, undiagnosed hypertension among all adults ranged from 19.4% to 35.5%; males from 18.7% to 35.6%; and females from 17.3% to 35.4%. Diagnosed hypertension among all adults was highest (quintiles four-five) in many provinces in the Java and Bali region (e.g., Jakarta, Banten, West Java, Yogyakarta, and Bali), several provinces in Kalimantan (e.g., East, North, and South Kalimantan) and Sulawesi (e.g., North Sulawesi, Central Sulawesi, and Gorontalo), and a province in Sumatera (i.e., Aceh). Undiagnosed hypertension among all adults was highest (quintiles four-five) in many provinces in Java (e.g., Jakarta, West Java, Central Java, East Java, and Bali) and Kalimantan (e.g., East, West, Central, and South Kalimantan), many provinces in Sulawesi (e.g., West, South, and Southeast Sulawesi), and two provinces in Sumatera and Papua. By sex, the patterning showed some differences. For instance, diagnosed hypertension among females was higher (quintile four) and that among males was lower (quintile two) in Bangka Belitung. In contrast, diagnosed hypertension among females was lower and that among males was higher in West Kalimantan. Similarly, undiagnosed hypertension among females was higher, and that among males was lower in North Sumatera, South Sumatera, and Lampung.

Analysis at the Provincial Level
Moreover, Table 1 compares diagnosed hypertension and undiagnosed hypertension by the level of poverty rates at the provincial level. The top box and bottom box compare the ten richest and poorest provinces. The provincial prevalence higher than the national level is shown in grey in each column. Of the ten wealthiest provinces, six provinces (e.g., Jakarta, Bali, South, North, and East Kalimantan) had higher prevalence than average for at least four indicators, while none of the ten poorest provinces did.
Moreover, Table 1 compares diagnosed hypertension and undiagnosed hypertension by the level of poverty rates at the provincial level. The top box and bottom box compare the ten richest and poorest provinces. The provincial prevalence higher than the national level is shown in grey in each column. Of the ten wealthiest provinces, six provinces (e.g., Jakarta, Bali, South, North, and East Kalimantan) had higher prevalence than average for at least four indicators, while none of the ten poorest provinces did.   Figure 2 and Tables 2 and 3 show results at the district level. Table 2 shows the characteristics of districts in terms of geographic indicators, socioeconomic indicators, and dependent variables (i.e., diagnosed and undiagnosed hypertension). Of the total of 514 districts in our analysis, 97 (18.9%) and 417 (81.1%) were urban (cities) and rural (regencies). The two regions where urban districts were dominant included Java (36.1% of 97) and Sumatera (34.0%). For the income variable, most of the urban areas (78.4%) were considered wealthy (quintiles four-five), but fewer than a third of rural areas (31.2%) were. Similarly, for education, 71.1% of urban areas had higher education (quintiles four-five), while only a third (32.6%) of rural areas did. In terms of hypertension, diagnosed prevalence was 7.9%, 5.5%, and 10.3%, while that of undiagnosed hypertension was 25.4%, 24.9%, and 25.8% among adults, males, and females. Relative to rural areas, diagnosed hypertension was significantly higher, but undiagnosed hypertension among females was significantly lower in urban areas. Diagnosed hypertension among adults, males, and females was 8.9%, 6.5%, and 11.2% in urban areas and 7.6%, 5.3%, and 10.1% in rural areas. Undiagnosed hypertension among females was 23.4% and 26.4% in urban and rural areas, respectively.   n/a n/a n/a n/a n/a n/a 6.  Figure 2 compares the prevalence of diagnosed and undiagnosed hypertension by quintile at the district level. For diagnosed hypertension, many districts in the provinces of Jambi, Riau, Bengkulu, Central Java, East Java, West Kalimantan, Central Kalimantan, South Sulawesi, Papua, and West Papua had higher hypertension among all adults (quintiles four-five). For undiagnosed hypertension, many districts in all provinces in Sumatera and Papua had higher prevalence among adults (quintiles four-five).

Analysis at the District Level
For socioeconomic disparity analysis at the district level, Appendices C and D compare districts with the lowest and highest diagnosed and undiagnosed hypertension. For diagnosed hypertension, the prevalence among adults ranged from 0% in Buton Tengah regency (Central Sulawesi province) to 20.8% in Sitaro Kepulauan (North Sulawesi). By sex, diagnosed hypertension among males ranged from 0% in Yahukimo and Pegunungan Bintang (Papua) to 15.8% in Tomohon city (North Sulawesi); that among females ranged from 0% in Buton Tengah (Southeast Sulawesi), Yahukimo, Dogiyai, and Mambramo Raya (Papua) to 27.0% in Sitaro Kepulauan (North Sulawesi). For undiagnosed hypertension, the prevalence among adults ranged from 7% in Puncak Jaya (Papua) to 43.2% in Hulu Sungai Tengah (South Kalimantan). By sex, undiagnosed hypertension among males ranged from 6.8% in Puncak Jaya (Papua) to 44.9% in Madiun city (East Java); that among females ranged from 6.2% in Puncak Jaya (Papua) to 44.6% in Ciamis (West Java). By urbanicity, districts with the lowest prevalence of diagnosed and undiagnosed hypertension for all adults, males, and females were rural. Similarly, most districts with the highest prevalence of diagnosed and undiagnosed were rural. By income, poverty rates among ten districts with the highest diagnosed and undiagnosed hypertension were averaged up to 10%, while those with the lowest prevalence were averaged up to 33%. Table 3 compares the associations between geographic/socioeconomic variables and diagnosed/undiagnosed hypertension. Districts in the least disadvantaged region had a significantly higher prevalence of both diagnosed and undiagnosed among all adults, males, and females, relative to the most disadvantaged region (e.g., Papua). Compared with Papua, districts in the Java region had 68%, 45%, and 76% higher diagnosed prevalence among adults, males, and females; they had 40%, 39%, and 40% higher undiagnosed prevalence (significant at 5% level). Moreover, results showed that districts in the Kalimantan region had the highest diagnosed and undiagnosed prevalence among all adults, males, and females in the country. For the income variable, results show that the richest districts had a higher diagnosed and undiagnosed prevalence among all adults, males, and females than the poorest ones (but not statistically significant in multivariable regressions). For the education variable, the relationships are mixed. Districts with the most education had 23%, 18%, and 25% significantly higher diagnosed prevalence among adults, males, and females than the least educated ones. However, districts with the least education had a 6% (i.e., 1/0.94 = 1.06) higher undiagnosed prevalence among females.

Discussion
Using nationally representative survey data of adults, we found the prevalence of overall hypertension was 33.3%, of which 76.3% were undiagnosed (i.e., 7.9% diagnosed and 10.3% undiagnosed). Global estimates showed similar hypertension prevalence in adults 30-79 years of age at 32% and 34% among women and men in 2019 [26]. In terms of undiagnosed hypertension, while considerably higher than in high-income countries such as the United States (19.7% in 2010), South Korea (33.4% in 2013), and Ireland (41.2% in 2011) [6,27], the prevalence in Indonesia was relatively similar to that in LMICs such as Nepal (50.4% in 2016), Bangladesh (59.9% in 2011 and 50.1% in 2017), and Peru (67.2% in 2019) [7,9,10].
By sex, diagnosed hypertension among females was 1.87 times higher compared with males (i.e., 5.5% males and 10.3% females), while undiagnosed hypertension was similar between both sexes (i.e., 24.9% and 25.8% among males and females). This finding aligns with evidence from other LMICs, such as Nepal, Bangladesh, and Peru, showing a significantly lower prevalence of undiagnosed hypertension among women [7,9,10]. This might be due to women having more interactions with the health systems (e.g., through antenatal, delivery, and postnatal care) and other population-based interventions more towards women (e.g., conditional cash transfers) [28,29].
We found significant disparities (geographic and socioeconomic) between the prevalence of diagnosed and undiagnosed hypertension across 514 districts. Diagnosed hypertension was higher by up to 22.6% in urban areas, while undiagnosed hypertension among females was higher by 11.4% in rural areas. Previous studies showed a higher prevalence of diagnosed hypertension in urban areas but a higher prevalence of undiagnosed hypertension in rural areas [7][8][9][10]. This is expected, as urban areas tend to have higher access to health facilities and healthcare professionals. However, many rural districts were among the top ten districts with the highest prevalence of diagnosed and undiagnosed hypertension, which may be due to similarities in economic development and mobility between rural and urban areas [30]. For example, the North Sulawesi, Minahasa and Minahasa Selatan regencies, which had similar income levels and were adjacent to Tomohon City, were found to have high rates of hypertension.
By region, the patterning is similar for diagnosed and undiagnosed hypertension. Districts in the most developed areas (i.e., Java and Bali) had up to a 76% and 40% higher prevalence of diagnosed and undiagnosed hypertension compared with the least developed areas (i.e., Papua, Nusa Tenggara, and Maluku). This is likely due to a higher burden of hypertension (diagnosed and undiagnosed) among higher socioeconomic levels of the population in more developed regions. By income, the richest districts had a higher prevalence of diagnosed and undiagnosed hypertension among all adults, males, and females than that of the poorest districts (although only statistically significant in bivariate analyses). By education, districts with the most education had up to a 25% higher prevalence of diagnosed hypertension, while those with the least had a 6% higher undiagnosed prevalence among females.
While evidence from LMICs are limited in the literature, our findings align with previous studies. Studies using provincial-level data in China showed a higher prevalence of hypertension in the least disadvantaged areas than that in the most disadvantaged ones [15,16]. Similar study at the provincial level in Thailand found a higher prevalence of hypertension in Bangkok and metropolitan areas than in less developed areas in the north and south regions [17]. On the contrary, studies from high-income countries found a higher prevalence of hypertension in the most disadvantaged areas [11,13,14]. Moreover, a higher prevalence of diagnosed hypertension among districts with the most education may be due to better health systems and access to health facilities [31]. In contrast, analyses at the individual level in Peru, Bangladesh, and Nepal found adults with low education had higher odds of undiagnosed hypertension [7][8][9][10]. Studies have also shown strong association between low education and cardiometabolic comorbidities and that education may be considered the best predictor of cardiovascular risk in people with hypertension [32,33].
Effective efforts are needed to reduce undiagnosed hypertension (and other NCD risk factors such as high cholesterol and diabetes) by sex, urbanicity, region, and socioeconomic status [34,35]. Efforts may include health system reforms such as enhanced primary health care in Malaysia or routine assessment national programs such as NHS Health Check in the United Kingdom [18,36]. Healthcare delivery reforms may also include integration with infectious disease platforms [37,38].
Our study is the first analysis from LMICs to compare the disparity (geographic and socioeconomic) in the prevalence of diagnosed and undiagnosed hypertension across over 500 localities. However, our study also has limitations. Because of the lack of information, our analysis could not conduct sub-group analysis by ethnicity [39]. Additionally, because of using cross-sectional data, our analysis could not conduct trend analysis. However, regardless of these limitations, our evidence is crucial for policymaking nationally and globally, especially in low-resource settings.

Conclusions
In Indonesia, a high prevalence of undiagnosed hypertension at 76.3% was found with different patterns of disparity observed between diagnosed and undiagnosed hypertension. Diagnosed hypertension was 1.87 times higher in females compared with males, while undiagnosed hypertension rates were similar between genders. Urban areas had up to 22.6% higher rates of diagnosed hypertension, while undiagnosed hypertension was 11.4% more prevalent among females in rural areas. Districts with higher education rates had 25% higher diagnosed hypertension rates, while districts with lower education rates had 6% higher rates of undiagnosed hypertension among females. The most developed regions had up to a 76% and 40% higher prevalence of both diagnosed and undiagnosed hypertension compared with the least developed regions. This study highlights the need for effective measures, including healthcare system reforms, to tackle NCDs in LMICs.

Conflicts of Interest:
The authors declare no conflict of interest.

Appendix A. Map of Provinces in Indonesia
Healthcare 2023, 11, x 11 of 18 our analysis could not conduct sub-group analysis by ethnicity [39]. Additionally, because of using cross-sectional data, our analysis could not conduct trend analysis. However, regardless of these limitations, our evidence is crucial for policymaking nationally and globally, especially in low-resource settings.

Conclusions
In Indonesia, a high prevalence of undiagnosed hypertension at 76.3% was found with different patterns of disparity observed between diagnosed and undiagnosed hypertension. Diagnosed hypertension was 1.87 times higher in females compared with males, while undiagnosed hypertension rates were similar between genders. Urban areas had up to 22.6% higher rates of diagnosed hypertension, while undiagnosed hypertension was 11.4% more prevalent among females in rural areas. Districts with higher education rates had 25% higher diagnosed hypertension rates, while districts with lower education rates had 6% higher rates of undiagnosed hypertension among females. The most developed regions had up to a 76% and 40% higher prevalence of both diagnosed and undiagnosed hypertension compared with the least developed regions. This study highlights the need for effective measures, including healthcare system reforms, to tackle NCDs in LMICs.