Adherence to treatment in a Western European paediatric population with haemophilia: reliability and validity of the VERITAS-Pro scale.

Treatment adherence in haemophilia is strongly associated with quality of life and the cost-benefit of treatment. Therefore, it is important to quantify and monitor it. This study aimed to validate a translation of the VERITAS-Pro cross-culturally and analyse treatment adherence in a Dutch population of paediatric haemophilia patients. Children aged 1-18 years with haemophilia were included from three Haemophilia Treatment Centres, on prophylactic clotting factor replacement therapy for more than 1 year. Parents and adolescents were analysed separately. The adherence scale for prophylactic therapy (VERITAS-Pro) was translated according to international guidelines. This instrument contains a total of six subscales ('Time', 'Dose', 'Plan', 'Remember', 'Skip' and 'Communicate') each with four items. Lower scores reflect higher adherence. Overall response rate was 85%, leading to a study population of 60 children. Mean age was 10 years (SD 4.1). Internal consistency reliability: Mean Cronbach's alphas were adequate (>0.70) for total score and the subscales 'Skip' and 'Communicate'. Item-own subscale correlations were stronger than most item-other subscale correlations. Convergent validity: Total scores were higher for non-adherent participants compared with adherent participants according to patient infusion logs (n = 48; P < 0.05). Test-retest correlations: Significant for all scales except 'Dose' (n = 58; P < 0.01). This study demonstrates applicability of VERITAS-Pro outside the United States, as total score and most subscales effectively quantified treatment adherence in a Dutch paediatric population on prophylactic therapy. Non-adherent respondents' total scores were significantly higher, demonstrating the ability of VERITAS-Pro to identify non-adherent individuals.