*Purpose: The Molecular Microscope Diagnostic System (MMDx) analyzes ribonucleic acid transcripts to provide sophisticated differentiation amongst T-cell mediated rejection (TCMR), antibody mediated rejection (AMR), injury and healthy tissue. However, little is known about its performance in dual organ transplant recipients.

*Methods: Endomyocardial biopsies (EMBx) and corresponding MMDx, results were collected from 12 adult heart transplant patients combined with either kidney (n=10) or liver (n=2) from our single center and were retrospectively reviewed. Rejection by EMB was defined as TCMR greater than 1R and/or AMR greater than pAMR0 utilizing ISHLT grading schematics.

*Results: A total of 16 specimen results from 12 patients were reviewed. There were concordant findings between EMBx and MMDx in 94% (15/16) of the specimens. Of these 16 specimens, 15 were negative for rejection on both tests. One patient’s heart/liver transplant results were discordant – EMBx negative for rejection and MMDx suggestive of TCMR (Table 1). After verifying compliance to medications, the patient’s immunosuppression was optimized with the addition of sirolimus following a multi-disciplinary discussion of all contradictory clinical and diagnostic data. One year follow up revealed no further TCMR detected by MMDx and EMBx remained negative for rejection as well.

*Conclusions: Conclusion: MMDx is a tool to potentially provide added accuracy in patient diagnoses in combination with other diagnostic data. In cases of discordant results, all data should be analyzed in a multi-disciplinary format to determine patient management. Larger studies are needed to validate these preliminary findings.

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