Development and validation of an immunosuppressant therapy adherence barrier instrument.

BACKGROUND: To decrease allograft rejection as a result of non-adherence to immunosuppressant therapy (IST), a valid and reliable instrument that measures solid organ transplant patients' adherence barriers is needed. METHODS: An immunosuppressant therapy barrier scale (ITBS) was developed to assess transplant patients' perceived barriers to IST adherence and was completed by 222 transplant patients who lived in Georgia, USA. A renal transplant population subset was used to test the ITBS reliability and validity. Scale reliability was estimated using Cronbach's alpha coefficient of internal consistency; scale dimensionality was assessed using principal components analysis. The criterion-related validity of the scale was assessed by relating subscale scores to adherence measures and graft rejection. Nomological validity was assessed by relating barrier subscales to specific patient factors. RESULTS: Two subscales that represented 'controllable' and 'uncontrollable' barriers were found. Cronbach's alpha coefficients demonstrated acceptable reliabilities of 0.93, 0.86 and 0.91 for the 'uncontrollable' and 'controllable' subscales, and for the entire ITBS, respectively. The ITBS subscales correlated negatively with a self-reported measure of IST adherence, IST serum concentrations and IST pharmacy refill adherence rate (P<0.01). The 'uncontrollable barrier' subscale was positively correlated to kidney graft rejection (P<0.01), thus demonstrating the ITBS's validity. Males and older patients reported more adherence barriers (P<0.05). CONCLUSIONS: The ITBS is a reliable and valid instrument that can be used to measure patients' perceived barriers to IST adherence.