**Background:** Hypertension affects approximately 1.3 billion adults globally, with over 60% living in low- and middle-income countries (LMICs). In Indonesia, hypertension prevalence among adults increased from 25.8% in 2013 to 34.1% in 2018, and prior studies found that nearly 70% of hypertensive adults aged 40+ were undiagnosed. While individual-level studies on hypertension disparities exist, district-level analyses—especially those distinguishing diagnosed from undiagnosed hypertension—are lacking in LMICs. This study aimed to assess geographic and socioeconomic disparities in diagnosed and undiagnosed hypertension across over 500 Indonesian districts.
**Methods:** This cross-sectional study used data from the 2018 Basic Health Survey (Riskesdas), which was representative at the district level. The survey employed a two-stage sampling procedure: 30,000 census blocks were randomly selected, and within each block, 10 households were systematically selected, yielding 624,563 adults aged 18 years and older (mean age 41.0 years, SD 15.5). Diagnosed hypertension was defined as ever being told by a doctor of having high blood pressure. Undiagnosed hypertension was defined as not having a prior diagnosis but meeting blood pressure criteria (systolic ≥140 mmHg or diastolic ≥90 mmHg). Independent variables included geographic region (Sumatera, Java/Bali, Kalimantan, Sulawesi, Papua/Nusa Tenggara/Maluku), urbanicity (city vs. regency), income (poverty rate quintiles), and education (net senior secondary enrollment ratio quintiles). Geospatial analyses (ArcMap 10) and ordinary least squares multivariable regression (STATA 15) were performed, with statistical significance set at 5%.
**Key Results:** Overall hypertension prevalence was 33.3%, of which 76.3% were undiagnosed. Diagnosed hypertension prevalence was 7.9% among all adults (5.5% males, 10.3% females), while undiagnosed hypertension was 25.4% (24.9% males, 25.8% females). At the provincial level, diagnosed hypertension ranged from 4.4% to 13.2% among all adults; undiagnosed ranged from 19.4% to 35.5%. At the district level, diagnosed hypertension ranged from 0% (Buton Tengah) to 20.8% (Sitaro Kepulauan), and undiagnosed ranged from 7% (Puncak Jaya) to 43.2% (Hulu Sungai Tengah). Urban areas had significantly higher diagnosed hypertension (8.9% vs. 7.6% in rural areas), while undiagnosed hypertension among females was significantly higher in rural areas (26.4% vs. 23.4%). By region, compared with Papua (the least developed region), Java had 68% higher diagnosed prevalence among adults (coefficient 3.05, p<0.01) and 40% higher undiagnosed prevalence (coefficient 7.72, p<0.01). Kalimantan had the highest diagnosed and undiagnosed prevalence overall (coefficients 3.65 and 9.36, respectively, p<0.01). For income, the richest districts had higher diagnosed and undiagnosed prevalence than the poorest, but these associations were not statistically significant in multivariable regressions. For education, districts with the most education had 23% higher diagnosed prevalence among adults (coefficient 1.14, p<0.01) compared with the least educated, while districts with the least education had 6% higher undiagnosed prevalence among females (coefficient −1.73, p<0.05).
**Clinical Implications:** The study reveals that in Indonesia, undiagnosed hypertension is extremely high (76.3% of all hypertension cases), far exceeding rates in high-income countries (e.g., 19.7% in the US) but similar to other LMICs. The disparity patterning differs between diagnosed and undiagnosed hypertension: more developed regions and higher-education districts have higher diagnosed rates (likely due to better healthcare access), while rural areas and lower-education districts have higher undiagnosed rates, particularly among females. These findings suggest that health system reforms—such as enhanced primary care, routine screening programs (e.g., NHS Health Check model), and integration with existing infectious disease platforms—are urgently needed to reduce the undiagnosed burden. Targeted interventions should prioritize rural areas, less educated populations, and females in disadvantaged regions to achieve SDG target 3.4.1 of reducing premature NCD mortality by one-third by 2030.