Nonadherence to Immunosuppressant Therapy of Kidney Transplant Candidate Patients: External Validation of the KATITA-25 Scale.

BACKGROUND: The self-administered Kidney AlloTransplant Immunosuppressive Therapy Adherence (KATITA-25) questionnaire is a multidimensional scale for use in the pretransplant setting that evaluates the predisposition to nonadherence of patients who are candidates to kidney transplant. The scale has shown adequate internal consistency and test-retest reliability. This study presents the results of an external validation study of the KATITA-25 scale. METHODS: Patients >18 y old scheduled for kidney transplant were included in this multicenter study. The KATITA-25 scale was administered before surgery and then at 3-mo posttransplantation for evaluation of scale sensitivity to change. At this time, 2 validated medication adherence scales were applied for assessment of concurrent validity. For evaluation of predictive validity, nonadherence to immunosuppressive medication was assessed at 6 and 12 mo after transplantation by 3 independent methods: patient self-report of nonadherence using the Morisky-Green-Levine Medication Assessment Questionnaire scale, serum trough levels of immunosuppressants, and pharmacy refills. RESULTS: Three twenty-two patients were available for evaluation of concurrent validity and 311 patients of predictive validity. After kidney transplant, the median KATITA-25 score decreased from 20 to 8 (P < 0.001), demonstrating scale sensitivity to change, and the KATITA-25 score showed correlation with the Basel Assessment of Adherence to Immunosuppressive Medication Scale score (Spearman's ρ 0.18, P = 0.002) and the Cuestionario para la Evaluación de la Adhesión al Tratamiento Antiretroviral scores (ρ -0.17, P = 0.002), confirming concurrent validity. The nonadherence rate was 57.6%. The scale predictive validity was demonstrated by the area under the receiver operating characteristics curve (0.68), sensitivity (59.8%), specificity (68.2%), and positive predictive value (71.8%). CONCLUSIONS: This external validation study of KATITA-25 scale provided evidence of sensitivity to change, and structural, criterion, and predictive validity.