Introduction

Hypertension and its complications represent key public health problems around the world especially among older adults. More than 40% of hypertensive person are older than 25 years [1]. Every year, 9.4 million deaths occur due to complications of hypertension [2]. Globally, diagnosis and treatment are relatively accessible and affordable, but even when patients are on treatment, there are health risks in the long term.

Different outcome measures can be applied to assess the effects of diagnosis and treatment, including health-state utilities, which are also core inputs for cost–effectiveness analysis of disease management. Notably, detailed measurements of utilities of hypertensive patients can support health economic evaluations of planned hypertension management programs. Currently, only limited information on health-state utilities of hypertensive patients is available for Asian countries, including Vietnam.

In many countries, the Short-form 36 version 2^TM (SF-36v2) questionnaire, as developed by Quality Metrics, has been applied to collect data on health-related quality of life (HRQoL) [3]. This instrument has also been applied for hypertensive patients in various countries [4–11], enhancing plausibility and acceptability of cross-country comparisons of HRQoL [9, 12, 13]. In Asia this instrument has already been validated in China, Singapore, Korea and the Philippines [14–17] which enhances plausibility that it is suitable for use in Vietnam.

In this study, we useSF-36v2^TM data from patients visiting a hospital out-patient clinic in an urban setting in Northern Vietnam to measure their HRQoL expressed in utilities. Furthermore, we aim to evaluate differences in health-state utilities related to characteristics of these patients to identify potential predictors.

Methods

Results

Main characteristics of patients

The main characteristics of the 712 patients who met the inclusion criteria and joined the study are presented in Table 1. Patients’ ages ranged from 41 to 80 years; half belonged to the group 60–69 years and 56% was female. Only 10% of patients still worked for wages. Among the patients, 66% did not meet their target BP at the time of the survey, while 70% had comorbidities and 11% had a history of stroke. The components of comorbidities was presented in S1 Table.

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Table 1. Characteristics of patients included in the study (n = 712).

https://doi.org/10.1371/journal.pone.0139560.t001

Health-state utilities

Mean utility was estimated at 0.73 (+/- 0.14) in this hypertensive population. Mean health-state utilities were significantly different with respect to gender and age groups (all p<0.01). Table 2 shows that relatively higher BP appeared to be associated with lower health-state utility at 0.73, 0.73 and 0.71 in the groups with target BP, stage one and stage two, respectively. However, these differences were not statistically significant (p = 0.42). Regarding comorbidities or history of stroke, we did not find significant differences between the mean health-state utilities of these groups (Table 2).

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Table 2. Distribution of health-state utilities by patients’ characteristic (n = 691).

https://doi.org/10.1371/journal.pone.0139560.t002

Controlling for other factors with adjusted ORs, we found that utilities in patients from 70 to 80 years old were lower than those of the younger groups; the difference between the oldest and youngest groups was statistically significant (Table 3; p = 0.03). Health-state utility in males was higher than in females even after adjustment for other factors (p = 0.002). Patients with a history of stroke exhibited an apparently lower health-state utility than patients without stroke, but the difference was not statistically significant (p = 0.79). Patients with more than three comorbidities had lower utilities than patients with no comorbidity, after adjustment (p = 0.01).

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Table 3. Predictors of health-state utilities in hypertensive patients (n = 691).

https://doi.org/10.1371/journal.pone.0139560.t003

Discussion

This study aimed to fill gaps in the evidence on utilities for populations with high BP in low- and middle-income countries, in particular Vietnam. Accurate utility scores are crucial for a planned analysis of cost-effectiveness of disease management.

The mean utilities of our population of hypertensive patients are somewhat lower than the utilities of the general population in Vietnam. For example, the health-state utility of an older population in a rural community in Vietnam, measured by EQ-5D, was 0.88 while the utility in our population was 0.73 [20]. However, this comparison should be interpreted with caution as the studies used different instruments to measure utility [9, 12, 13]. Also, in comparison with other populations in Asian countries, estimated health-state utility is lower in our hypertensive population. For example, a general population in Singapore had mean health-state utility of 0.80 (+/-0.12), using the same method for health-state utility measurement [21].

Differences in utilities seem associated with age, gender, and a high number of comorbidities. However, no such statistically significant differences are found among BP-stages or with presence of history of stroke. Health-state utility among these hypertensive patients differed from an Australian study in which the utility of 0.63 was lower than the utility of 0.73 in our population, using the same instrument and method [22]. However, the population in that study consisted of prisoners and persons with an impaired mental health status, which may explain the lower health-state utilities. Results in other studies vary in health-state utility. For example, health-state utility in a hypertensive population (Beaver Dams study) was 0.72 or 0.83, measured with the Quality of Well-Being (QWB) and time trade-off (TTO) methods, respectively [13]. In a Swedish population with high BP, health-state utility was 0.73 when using a rating scale and 0.81 when using TTO [6]. In a Nigerian hypertensive population, it was relevantly lower at 0.35(+/-0.42), using the HUI3 method [23]. Again, these comparisons should be interpreted cautiously because different instruments and methods were applied [6]. Finally, in contrast with the aforementioned Nigerian study, in our study, health-state utilities do not significantly differ for different BP-levels. The methods of analysis between these two studies differed, with BP specified as a continuous variable in the Nigerian study but as a categorical one in our study [23]. In addition, in our study BP was measured only once at the time of examination; we do not know adherence to medication in this population or whether target-BP was achieved.

As expected, patients with a history of stroke have lower utilities than those without such a history in our study, however lacking statistical significance (likely due to relatively small numbers) [23]. Our finding that history of stroke does not significantly predicts utilities in our study population is in line with a similar study in a Swedish population [6]. Next to small numbers, a further reason may be that severity of health impacts and complications after stroke were relatively mild and all patients generally recovered.

In general, older patients have lower utilities than younger ones in our study. When controlling for sex and health status, the only significant difference found is between the oldest group and youngest group. Obviously and in general, utility decreases with age and in other studies it has indeed been quantified that each year of increasing age was reported to reduce health-state utility [22, 23]. In line with other studies, males have 0.03 higher mean health-state utility than females [22, 23]. We find an association between comorbidities and utilities, but this association is only manifest for patients having more than three comorbidities. In the Australian study, researchers reported that each increase in the number of comorbidities was associated with reduced utility [22]. It should be noted that our results appear without controlling for other variables that may affect HRQoL, such as body mass index, educational level, smoking, marital status, income/socioeconomic factors, serious events in the past, antihypertensive drugs, household position and awareness of hypertension [5, 9, 11, 20, 22, 24–27].

Regarding the limitations of the study, it should be mentioned that reliability and validity of applying the equation to obtain utilities from SF-36 in Vietnam should be investigated further, as it was developed for a Western population. We should be aware of potential similar problems as reported for other instruments [28, 29]. However, it has already been used in other Asian countries [21, 30] and currently does seem the optimal approach, most likely being acceptable for our measurements. In Vietnam, hypertension also occurs below the age of 40 years. However, we limited our study to 40 and over as younger patients were not available in the survey. Despite specific questions in the questionnaire, we were unable to get reliable estimates on the exact number of years since diagnosis of hypertension. Patients seemed unable to exactly recall year of diagnosis. Therefore, an analysis on the relationship between health utilities, duration, seriousness of progressive disease and burden of comorbidities overtime could not be performed in this study. Finally, due to scarce resources, capacity and funds, data collection lasted only two months, which may have influenced the type of patients included with respect to how they managed their hypertension in this specific hospital.

Conclusions

Health-state utilities found among hypertensive patients in Vietnam were similar to those found in other international studies. It is suggested that lower of health-state utilities exist among those patients who were older, female or had more than three comorbidities in comparison with respective reference groups. However, further research for confirmation is required. The data from this study provide a potential reference on health-state utilities of hypertensive patients in Vietnam as an input for future cost-effectiveness analysis of interventions. Also, it may serve as a reference for other similar populations, especially in the context of similar environments in low income countries.

Supporting Information

Acknowledgments

Our thanks go to the Outpatient Department at Thai Nguyen General Hospital for their co-operation during the study. We also thank Professor John E Brazier for providing the algorithm to transfer SF-36v2^TM to health-state utilities score.