Evolving the surveillance and workup of heart transplant rejection: A real‐world analysis of the Molecular Microscope Diagnostic System

The Molecular Microscope Diagnostic System (MMDx) analyzes RNA transcripts of transplanted heart tissue to differentiate among T cell–mediated rejection (TCMR), antibody‐mediated rejection (AMR), injury, and healthy tissue. However, little is known about its performance in relation to other modalities in a real‐world heart transplant population. We evaluated whether MMDx performs in agreement with other validated modalities. Two hundred and twenty‐eight corresponding endomyocardial biopsies (EMBx) and MMDx specimens from 135 adult heart transplant patients were retrospectively reviewed with correlating donor‐derived cell‐free DNA (dd‐cfDNA). Rejection was classified on EMBx in 29 specimens (TCMR ≥ 2R and/or AMR ≥ 1), on MMDx in 56 specimens, and in 74 values with dd‐cfDNA ≥0.20%. Despite moderate agreement between EMBx and MMDx (84% agreement, Cohen’s kappa, 0.48, p