Serial biopsy controlled evaluation of fine needle aspiration in renal allograft rejection

Transplant fine needle aspiration (FNA) cytology has been suggested as a method for monitoring intrarenal changes of acute rejection after transplantation. We studied this technique by sampling dog renal allografts daily with simultaneous FNA's and core needle biopsies from the time of transplantation to complete rejection. Individual FNA's were analyzed by the increment method, subtracting peripheral white blood cell counts from aspirated white blood cell counts to define the composition and extent of interstitial mononuclear infiltrate. The increment for each mononuclear cell type was corrected by a factor related to its immunologic relevance and the new values summed to produce the total corrected increment, an index of rejection. FNA findings were compared to histologic sections graded 0 to 4 according to the extent of mononuclear infiltrate that was present. FNA sample adequacy was assessed by the aspirate sampling index (ASI), the concentration of renal tubular cells per high power microscopic field. Mean FNA increments for all mononuclear cell groups increased as rejection progressed histologically. Mean total corrected increment ranged from 0.9 with no rejection to 9.8 with grade 4 rejection (R = 0.73; p = 0.001). Mild and moderate infiltrates were detected more accurately when ASI was at least 0.25, while denser infiltrates could be detected in samples with lower ASI. These findings indicate FNA can identify the mononuclear infiltrate associated with acute rejection and the FNA score correlates with the magnitude of the infiltrate if the parenchymal component of the sample is large enough. The ASI is of value in evaluating the samples and reducing the likelihood of false-negative interpretations.