*Purpose: AlloMap (AM) is a peripheral blood gene expression profiling (GEP) tool used for the assessment of acute cellular rejection in heart transplant recipients (HT). GEP is clinically indicated with steroid use <20mg because of the incorporation of 3 steroid sensitive genes in the algorithm. The objective of this study was to characterize the changing patterns of early GEP scores to ascertain whether differences in steroid use may be a factor.

*Methods: All clinical GEP test scores (sent to CareDx) between January 2006 and November 2021 were reviewed. Results were grouped into 3-time periods; 2006-2010, 2011-2015 and 2016-2021. Means were considered against months post-transplant (MPT) and assessed using student’s t-test. Prednisone dose was described from the SHORE registry at >2 MPT, 2-3 MPT, 3-6 MPT, >6 MPT to assess current steroid clinical practice.

*Results: 197,658 GEP results were examined with a median GEP score of 30.77. Mean 2-month GEP score was 21 in 2006-2010 compared to 26 in 2016-2021 (p<0.0001) and the mean 6-month GEP score was 27 in 2006-2010 compared to 29 in 2016-2021 (p<0.0001). Median steroid dose was: 20mg (>2 MPT; n=835), 12.5mg (2-3 MPT; n=1289), 7.5mg (3-6 MPT; n=2513) and 2mg (>6 MPT; n=2668).

*Conclusions: Since 2006, there has been a progressive increase in the AM scores across at 2- and 6-months post-HT. These differences were mirrored by decreasing steroid doses across these same time periods. Interpretation of changes in AM scores, particularly changes early post-HT, should reflect this change in clinical practice.

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