*Purpose: Kidney transplant recipients (KTR) take a daily regimen of immunosuppression medication that almost inevitably includes tacrolimus (TAC). Non-adherence to TAC is a strong predictor of graft loss. To minimize TAC non-adherence, tools to screen patients are needed. The Patient Reported Outcome Information System (PROMIS®) Medication Adherence Scale (PMAS) was recently developed with input from KTRs. Here, we report on the validation of the PMAS among KTRs taking oral TAC.

*Methods: This was a prospective observational longitudinal analysis; 58 KTRs were surveyed from a single transplant center every 2 months starting at 4-5 months post- transplant and continuing until 1-year using the PMAS instrument, which has 9 items focusing on various aspects of medication adherence (e.g., remembering to take medications, taking even when there are side effects). Each item has 5 response options, and 8 of the 9 items are summed to create a score ranging from 8-40 (higher scores mean better adherence). We estimated correlations between each item and the total PMAS score, and then calculated Cronbach’s alpha reliability of the PMAS score. We then estimated correlations between the PMAS score and coefficient of variation (CV) % for TAC in the blood trough and with time in therapeutic range (TTR) for TAC. We also compared mean PMAS scores between groups expected to differ in their TAC adherence levels, including a published cut-off CV% >41% vs. <41% and reporting that the cost of their TAC has been a hardship (“Not at all”/”A little bit” vs. “Somewhat”/”Quite a bit”/”Very much”).

*Results: The mean age of participants was 53 years (range = 25-72) and most were on Envarsus extended release (n=53, 91%). The mean PMAS score was 38.7 (SD=2.2). Item-to-total PMAS score correlations (excluding MedAd5; “I took this medicine as recommended”) were strong (r range = 0.60-0.77). The internal consistency reliability of the 8 items was excellent at 0.91. The correlation with CV% was high at -0.42 but was lower with TTR at 0.28. Significant differences in mean PMAS scores were observed between patients with CV% >41% vs. <41% (difference = -1.3; p=0.02) and reporting higher and lower financial hardship due to TAC (difference = -1.9; p=0.01).

*Conclusions: The PMAS instrument evidenced reliability and validity among KTRs on oral TAC. This evidence instills confidence around the use of PMAS to screen for non-adherence in clinical settings, and as a potential outcome in studies testing adherence-promoting interventions.

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