Objectives: This study aimed to explore the psychometric properties of the Vietnamese comprehensive score for financial toxicity (COST) among people with chronic disease.

Methods: We conducted a cross-sectional study involving 1,022 people with chronic disease in Can Tho City. Exploratory and confirmatory factor analyses were performed to assess construct validity, while Cronbach’s alpha was used to evaluate the scale’s reliability.

Results: Our EFA identified two factors explaining 55.0% of the cumulative variance. CFA indicated that the adjusted two-factor model demonstrated a good fit, with a comparative fit index of 0.96, a Tucker-Lewis index of 0.94, and an RMSEA of 0.062. COST scores were significantly correlated with monthly income (p < 0.001). The COST measure demonstrated good internal consistency, with a Cronbach’s alpha coefficient of 0.82.

Conclusions: The COST is a valid and reliable measure for people with chronic disease in Vietnam. This scale can be applied in clinical practice to assess the impact of financial toxicity among people with chronic disease.

chronic disease, financial toxicity, validation, Vietnam

Chronic diseases, especially major non-communicable ones, which are caused by genetic, physiological, environmental, and behavioral factors, are the leading cause of death globally, accounting for about 41 million deaths annually (71% of all deaths) (World Health Organization 2024). Chronic diseases such as diabetes, heart disease, stroke, and cancer have been, and continue to be, some of the major causes of morbidity and mortality worldwide (Hacker 2024). Vietnam has begun to face an aging population, which, together with other risk factors such as tobacco use, alcohol consumption, and a diet high in salt and fat, contributes to the increasing burden of chronic diseases (Ba et al. 2019; Hoy et al. 2013). Chronic conditions are the leading causes of death in the country (Ba et al. 2019), with the leading causes per 100,000 population including stroke (167.6), ischemic heart disease (65.6), chronic obstructive pulmonary disease (36), and diabetes mellitus (31.2) (World Health Organization 2021).

Chronic diseases impose a high and catastrophic cost burden on patients and their families (Okediji et al. 2017). The cost of chronic disease is estimated to reach USD 47 trillion worldwide by 2030 (Hacker 2024). Compared to high-income countries, the burden of such diseases is more severe in low- and middle-income countries, including Vietnam, due to multiple challenges in appropriate treatment, prevention, and early detection (Ito et al. 2022). Because chronic diseases require prolonged treatment, they impose a greater financial burden than acute diseases (Ito et al. 2022). This financial burden has been found to predict and impair quality of life and cost-related treatment nonadherence (Xu et al. 2024). In Vietnam, a report found that the presence of chronic conditions was associated with a 2.5-fold higher likelihood of cost-related medication nonadherence compared to those without chronic conditions (Tran et al. 2025). Therefore, screening and assessing the level of financial burden due to chronic diseases is necessary to understand the economic impact that patients are suffering and thereby suggest necessary intervention solutions. This financial burden raises ethical concerns about equity in access to care, as patients in lower socioeconomic groups are disproportionately affected (Ruger 2012), and highlights the responsibility of health systems to ensure financial risk protection and equitable access to essential services.

The term “financial toxicity” was first introduced in 2009 (Sideris et al. 2025) and is increasingly used to reflect the economic burden borne by individuals with chronic diseases (Tran et al. 2024a). Financial toxicity refers to the adverse effects experienced by patients as a result of the financial demands associated with cancer care. It encompasses both direct expenses paid out-of-pocket and indirect costs, along with shifts in a person’s or household’s financial stability caused by the process of diagnosis, treatment, survivorship, or palliative care. These financial pressures can lead to both physical and emotional distress and may influence health-related decisions, potentially resulting in poorer treatment outcomes (COSA 2022). To measure financial toxicity, the comprehensive score for financial toxicity (COST) scale was developed; however, its original version was constructed for the cancer population (de Souza et al. 2014). The COST scale is a unidimensional instrument consisting of 11 statements that assess patients’ perceived financial toxicity. Respondents rate each statement on a 5-point Likert scale ranging from 0 (“not at all”) to 4 (“very much”), with total scores ranging from 0 to 44; lower scores indicate greater financial toxicity. In recent years, this scale has also been applied to other chronic diseases such as diabetes (Patel et al. 2022) and chronic kidney disease (Silva et al. 2023), as well as disease groups related to cardiometabolism, pain management, pulmonary problems, immunology, and many other medical fields (Pavela et al. 2021). In Vietnam, the COST scale has been localized and validated in cancer patients. However, its validity to assess financial stress in other chronic diseases in Vietnam has not been explored (Tran et al. 2024a). Given the growing burden of financial stress in chronic disease management and the demonstrated utility of the COST instrument in oncology, evaluating its application in broader chronic disease populations is both timely and necessary. Therefore, the aim of this study was to explore the psychometric properties of the Vietnamese COST among chronic patients.

This study is the first, to our knowledge, to provide evidence of the reliability and validity of a financial stress measurement instrument related to the management of various chronic diseases in Vietnam.

EFA revealed a two-factor structure of the COST scale in this study, including “negative psychosocial response” (comprising seven items: COST 2, 3, 4, 5, 8, 9, and 10) and “positive wealth status” (comprising four items: COST 1, 6, 7, and 11). The grouping of items into each factor, as well as the naming of the two identified factors, is similar to results reported in previous studies (Tran et al. 2024a; Yu et al. 2021).

The CFA results also support the two-factor structure, as demonstrated by satisfactory fit indices for CFI, TLI, and RMSEA. In the initial development of the scale, the structure was reported as unidimensional (de Souza et al. 2014). Therefore, we also tested the fit of the one-factor model, and the results showed that its fit indices were inferior to those of the two-factor model. In addition, the one-factor model explained only 37.8% of the variance, whereas the two-factor model explained 55%. This level of variance explained by the two-factor model is consistent with the acceptable threshold of at least 50% of total variance explained by the retained factors (Streiner 1994). Therefore, the Vietnamese version of COST with two factors was considered appropriate, consistent with findings from other studies (Patel et al. 2022; Tran et al. 2024a).

COST also differentiated between patients in the low- and high-income groups, consistent with the study hypothesis and previous findings (Kim et al. 2025). Income is a factor affecting financial toxicity, as individuals with limited financial resources are more vulnerable to the burden of medical costs (Tran et al. 2024b). These results further support the known-groups validity of the COST-PROM tool in assessing financial toxicity specifically and reliably among patient groups with varying economic backgrounds.

The internal consistency of the COST was comparable to both the initial validation of the instrument (de Souza et al. 2014, 2017) and studies that validated the instrument in other languages (Fradelos et al. 2023; Yu et al. 2021), including Vietnamese (Tran et al. 2024a). The adjusted item-total correlations, which were within acceptable limits, indicated that all 13 items of the COST contributed to the measurement of financial impact.

In this study, the average COST score was 25.47, which exceeded values reported in earlier research (Patel et al. 2025; Silva et al. 2023). This result may indicate that participants experienced lower financial distress, potentially influenced by factors such as comprehensive health insurance coverage or reduced treatment costs. By 2024, more than 94.2% of the Vietnamese population had participated in health insurance, moving closer to the goal of universal health coverage (Viet Nam Social Security 2025). These findings underscore the importance of calibrating the COST scale according to population characteristics to ensure adequate sensitivity in assessing financial toxicity.

The validated Vietnamese version of the COST tool in this study may be useful in both clinical and public health settings. For example, it can serve as a screening instrument to identify chronic patients experiencing financial difficulties. Early detection is important for guiding interventions by clinicians and policymakers, including financial counseling and referral to social support services. This approach can help promote more comprehensive and patient-centered care by addressing the financial burden of treatment.

This study achieved a high response rate (85.2%), which enhances the reliability of the results and reduces the risk of non-response bias. With a sample size of 1,022 individuals representing diverse chronic illnesses, the study offers insights that may be applicable to a wide range of patients living with long-term conditions.

Several limitations should be noted. First, due to its cross-sectional nature, the study cannot capture changes in financial toxicity over the course of treatment. Second, although the initial selection of study sites was conducted randomly to enhance representativeness, the use of convenience sampling to recruit patients at each site may introduce selection bias. Our sample consisted primarily of patients with chronic conditions, with small sample sizes for some specific conditions. This limits the ability to generalize our findings to specific chronic conditions. Third, the study did not assess convergent validity, as it did not compare COST with related measures such as life treatment burden, psychological distress, or quality of life. This represents a significant limitation, as convergent validity is critical for confirming the conceptual relevance of patient-reported outcome measures. Future studies should examine the relationship between COST and these related measures to support its validity in different clinical and cultural contexts.

The study confirms the validity and reliability of the Vietnamese version of the COST instrument in a chronic patient population. This is the first validation study of COST in relation to multiple chronic conditions in Vietnam. The scale can be used in diverse healthcare settings–such as outpatient clinics, community health programs, and health insurance eligibility screening–to measure the impact of financial toxicity in chronic patients, thereby providing a basis for interventions addressing financial toxicity in chronic diseases. Future studies may apply this validated tool for longitudinal tracking of financial toxicity, exploring differences across specific disease types and between rural and urban populations, or integrating it with electronic health records.

We acknowledge Can Tho University of Medicine and Pharmacy, Nam Can Tho University, and the patients for their collaboration in this study.

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statements

The authors declared that no clinical trials were used in the present study.

The authors declared that no experiments on humans or human tissues were performed for the present study.

The authors declared that no informed consent was obtained from the humans, donors or donors’ representatives participating in the study.

The authors declared that no experiments on animals were performed for the present study.

The authors declared that no commercially available immortalised human and animal cell lines were used in the present study.

Use of AI

No use of AI was reported.

Funding

No funding was reported.

Author contributions

Conceptualization: MHL, MCN, VLN; Methodology: MHL, TTHN; Investigation: MCN, TTHH, NDLT; Resources: TTHN, VLN, YNT; Writing–original draft: MHL, TTHN, MCN, YNT, NDLT, VLN; Writing–review and editing: MHL, TTHN, MCN, YNT, NDLT, VLN.

Author ORCIDs

Minh Huu Le https://orcid.org/0000-0003-2618-9377

Tuyen Thi Hong Nguyen https://orcid.org/0000-0002-1332-5862

Van Lanh Nguyen https://orcid.org/0009-0004-7307-7882

Data availability

The data supporting the findings of this study are available from the corresponding author upon reasonable request.