Cross-cultural adaptation, validation, and measurement invariance of the Italian version of the diabetes health literacy scale among Italian-born and foreign-born adults with type 2 diabetes mellitus

Aims: Health literacy (HL) is a key determinant of diabetes self-management and clinical outcomes in type 2 diabetes mellitus (T2DM). The Diabetes Health Literacy Scale (DHLS) is a 14-item instrument assessing informational, numeracy, and communicative HL, with established validity in Korean, Persian, Malay, and Chinese populations. This study aimed to translate and culturally adapt the DHLS into Italian and evaluate its structural validity, internal consistency, construct validity, and measurement invariance across Italian-born and foreign-born adults with T2DM. Methods: A total of 300 adults with T2DM were recruited from two outpatient diabetology clinics in Florence, Italy. DHLS translation followed ISPOR guidelines with cognitive debriefing. Psychometric evaluation followed COSMIN recommendations and included confirmatory factor analysis, McDonald's omega, Pearson's correlations with comparator instruments, and multigroup confirmatory factor analysis (CFA). Results: CFA supported the three-factor second-order structure (CFI = 0.921, RMSEA = 0.077). Internal consistency was satisfactory across domains (ω = 0.759-0.868) and excellent for the total scale (ω = 0.940; ωH = 0.770). All convergent validity hypotheses were supported. Multigroup CFA demonstrated configural but only partial metric invariance across birthplace groups. Conclusions: The DHLS-IT is a valid and reliable instrument for assessing diabetes HL in Italian adults with T2DM. Partial metric invariance cautions against direct latent score comparisons between Italian-born and foreign-born patients.