This study demonstrates that the distance from the super-tertiary center is the most important factor for the patients’ chances of receiving PA screening. Whereas the presence of specialist (endocrinologist) and the cultural differences are not. Meanwhile, the provinces located on the west coast adjacent to the Andaman Sea (Phuket, Phang Nga, and Satun) have the highest incidence of PA.
The effect of distance or geographical barrier to healthcare services is supported by previous studies conducted in both developing and developed countries (12–15). Costs and difficulty in transportation might explain this finding. Although public health insurance covers most of the hospital expenses such as medical services and medicines, which are explicit costs, there remain the implicit costs that still put a burden on the patients. In general, the patients have to pay for transportation costs, and additional costs for accommodation in cases requiring an overnight stay. The government and other insurance schemes do not subsidize all these invisible costs, and they tend to be higher for the patients living far away from the healthcare center. That is, the farther they live, the more they pay. Since tertiary or super-tertiary centers are usually located in an urban area, with a middle- to high-income population, the most affected patients are the poor from rural areas. Likewise, public transportation is not available for all routes and times. Under these circumstances, some patients might refuse a referral to the healthcare center as it is accompanied by a heavy burden.
Nevertheless, low screening rates in Ranong, Chumphon, and Krabi could be attributable to the presence of alternative healthcare centers in Bangkok, the capital city of Thailand. The patients from these three provinces can easier access Bangkok than Songkhla by road and air. The decision of patients to obtain diagnosis and treatment outside their health care region is another effect of the distance.
The absence of the association between PA screening and the availability of endocrinologist suggests two possibilities. The physicians may be aware of PA while taking care of hypertensive patients, and also the existing referral system is active. There is also no effect of religious and cultural beliefs on PA screening. The phenomenon suggests that the investigation process of PA does not involve sensitive religious and cultural issues as it does in cervical cancer screening in terms of sexual exposure and reproduction, which leads Muslims to be reluctant to seek health care (16, 17).
It is noticeable that the population living in provinces adjacent to the Andaman Sea has high incidence of PA, even though they have a lower chance of receiving PA screening than people living in Songkhla or other nearby areas. The contributing causes should be assessed from both external and internal factors. One possible external factor is that these three provinces are popular tourist destinations with excellent transportation facilities and have high per capita income. Therefore, the people living in this area might have a better opportunity to gain access to the super-tertiary center. It should be noted that Phuket has a large medical center that can readily perform both screening and confirmatory tests of PA investigations by endocrinologists. Hence, the patients in Phuket and Phang Nga with negative screening tests were unlikely to be referred to Songklanagarind Hospital and the estimated screening rates using the PAC/PRA results in our center might be underestimated. Likewise, there is a high probability of having PA in patients who were referred to our hospital, leading to the selection bias of cases. Nonetheless, this is not evident in Satun, a small province further south towards Songkhla on the border with Malaysia, where Songklanagarind Hospital is the nearest and biggest hospital accessible to the patients.
Regarding the internal factors, people living in this area include the islanders in the Andaman Sea, such as sea gypsies with different genetic transmission from most Thais. These groups of islanders tend to have a diverse society and culture, i.e., consanguinity. Regrettably, we did not collect these details, and additional data evaluating this population should be studied in the future.
The strength of our study is that it was a spatial epidemiological study representing Thailand’s health inequity despite the presence of various public health insurance covering the entire Thai population. The results of this study could encourage policymakers to develop a strategy, which decreases barriers to healthcare access. For example, there should be a transfer system of blood tests for PA investigation, including teleconsultation to interpret laboratory results. The goal of the change is to reduce the number of patients being referred to the super-tertiary hospital. Developing a predictive scoring system of PA is also another good case to be implemented (3). However, the current scoring system needs further validation study before being applied to routine clinical practice. According to the current hypertension screening program in Thailand, there is still limitation in effective coverage in hypertension screening management (18). Future development of the program should be proposed together with incorporating PA screening into the program of MOPH.
There are some limitations to this study. Firstly, it represented only Southern Thailand and could not be applied to other areas with different nationality, geographic area, and the healthcare system. Secondly, the incidence of PA in some provinces, especially Ranong, Chumphon, and Krabi, might be underestimated as the patients had a probability to be referred to Bangkok. Thirdly, the information about PA subtype, genetic study, and details of socio-economic-cultural data were not collected as described above. Further research about these details should be conducted in the future.