RESUMEN
BACKGROUND: Non-adherence to immunosuppressive medication is associated with graft loss and death. The simplified medication adherence questionnaire (SMAQ) is a short and reliable instrument for assessing adherence to medication. OBJECTIVE: Validation of a version of the SMAQ instrument adapted for use in transplant patients in a sample of kidney graft recipients. METHODS: Observational, longitudinal prospective study in 150 renal transplant patients on tacrolimus, over 18 years old, who had received a graft at least one year before. Basic sociodemographic and clinical data were recorded; patients completed the SMAQ twice (administered by doctor/nurse) and self-administered the Morisky-Green scale. The analysis database included 144 patients that met selection criteria and that provided the required data. Descriptive characteristics for all recorded parameters and psychometric characteristics of the questionnaire (reliability and validity) were studied. RESULTS: Mean age in the sample was 50.63 (12.44) years, 60.42% were men. Some 20.14% of patients had sub-target tacrolimus levels (<5 ng/ml), and unjustified variations in immunosuppressive drug levels were reported for 13.48%. Regarding SMAQ results, 39.01%/41.84% of patients were non-adherent (doctor/nurse administration); 22.38% according to the Morisky-Green scale. Interobserver agreement (kappa) was 0.821 (P<.001). The Cramer's-V statistic for convergent validity was 0.516 (P<.001). SMAQ scores were associated with unjustified variations in tacrolimus levels. In the prediction of tacrolimus levels (target vs subtarget), SMAQ compared to Morisky-Green provided a better classification of patients, with greater sensitivity and lower specificity. CONCLUSION: The questionnaire provides good levels of validity and interobserver agreement. An enhanced sensitivity is advantageous to better detect non-adherent patients for a better follow-up.