Objectives - To describe the clinical signs and histopathologic features of renal allograft rejection in cats, and to provide a historical, untreated control group for use in future studies of feline renal allograft rejection. Animals - Fourteen adult research cats. Methods - Renal transplantation and bilateral nephrectomy were performed in pairs of immunogenically mismatched cats. A physical examination was performed, and packed cell volume, total protein, and plasma creatinine concentrations were measured each day after surgery. The cats were euthanatized when plasma creatinine concentration exceeded 7 mg/dL or when weight loss exceeded 20%. Renal histopathology was scored according to the Banff 97 criteria by 3 pathologists. Results - Nine cats completed the study. Plasma creatinine exceeded 7 mg/dL in 5 cats, weight loss exceeded 20% in 3 cats, and 1 cat was found dead. Clinical signs in cats with rejection were nonspecific or absent. Rectal temperature decreased by 0.8 ± 0.5°C in the 24 hours before euthanasia. The pathologists agreed on the allograft histopathologic category in 6 of 9 cats. The histologic concensus was acute/active rejection in 8 cats and normal in 1 cat. Median survival time of the 8 cats with histologically confirmed allograft rejection was 23 days (range, 8-34 days). Conclusions and Clinical Relevance - Renal allograft rejection is associated with minimal clinical signs. Therefore, plasma creatinine concentration should be measured routinely in patients with a functioning allograft. An increase in plasma creatinine concentration is highly suspicious for allograft rejection, although a biopsy of the renal allograft is needed for definitive diagnosis.
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