*Purpose: The TruGraf kidney blood gene expression test is a well-validated non-invasive biomarker to detect immune quiescence thus ruling out silent subclinical rejection in stable kidney transplant recipients, eliminating the need for a surveillance biopsy. The TruGraf test is a microarray-based assay that analyzes the peripheral blood gene expression profile (GEP) and provides a binary result of either TX (Transplant eXcellence) or not-TX (not Transplant eXcellence). A TruGraf TX result correlates with a high degree of confidence (NPV 89%) to a surveillance biopsy result showing no evidence of rejection. Given this intended context of use, TruGraf validation was performed exclusively in cohorts of patients that have a stable renal function defined as SCr <2.3 or <20% increase as compared to the average of previous 3 SCr results. The intent of this study was to evaluate performance in the setting of unstable kidney function (AKI) and for-cause biopsies.

*Methods: This is a retrospective evaluation of serial TruGraf gene expression testing done on 10 patients with evidence of AKI (SCr >2.3 or >20% increase over the average of previous 3 SCr values). From Dec 2019 to Jun 2020, a total of 23 tests were drawn on these patients as an adjunct to clinical and laboratory assessment.

*Results: Of the 23 TruGraf tests done, 13 (56%) were a TX result while 10 (43%) were a not-TX result. There was a total of 11 biopsies done on 9 patients with the majority of biopsies (n=9) being done within 2 weeks of the TruGraf test date. One patient with a TX result did not have a biopsy done during this observation period. The GEP result of TX or Not-TX correlated with biopsy results in 10 of the 11 samples. Of these 10 biopsy results, a TX result was consistent with no rejection on biopsy (n=4). The Not-TX result (n=6) correlated with positive biopsies with histology for borderline rejection (n=1), mixed TCRM/AMR (n=2), AMR (n=2), and TCMR (n=1). In the single sample with a false negative TX result, the patient’s biopsy was positive for AMR with C4d2, PTC-. The performance metrics in this patient population were: sensitivity 85.71%, specificity 100%, and accuracy 90.91%.

*Conclusions: As expected, the TruGraf GEP analysis is consistent along the continuum of rejection and is inclusive of both subclinical and clinical acute rejection. While limited by a small sample size, the TruGraf test has a high degree of accuracy in the setting of AKI and appears to have stronger performance as compared to the context of stable kidney function.

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