Immunocytology of urinary sediments as a method of differentiating acute rejection from other causes of declining renal graft function

We have previously reported that during acute rejection of renal allografts T lymphocytosis and increased HLA-DR expression on tubular epithelial cells can be demonstrated in urinary sediments by incubating cytospin preparations with monoclonal antibodies against T cells and HLA-DR antigen in an indirect alkaline phosphatase technique. We now tested whether immunocytological analysis of urinary sediments can be used to differentiate acute rejection from other causes of declining graft function. For this we retrospectively selected, from a series of urinary samples that were taken either at random or as part of a longitudinal study in unselected graft recipients, those specimens that were taken at the time of increasing creatinine levels, and compared the original immunocytological diagnosis, made without knowledge of clinical data, with the final clinical one. In 44 of 74 evaluable cases an immunocytological diagnosis of rejection was made, which in 37 patients was consistent with the eventual clinical diagnosis. In 28 of 30 cases the diagnosis no rejection proved to be correct. This indicates a sensitivity of 95% and a specificity of 80% for the immunocytological diagnosis of rejection. Of 38 patients who underwent a renal core biopsy, the immunocytological diagnosis was consistent with the histological diagnosis in 36 cases (31 rejections, 5 no rejections). In this subgroup the sensitivity of the immunocytology was 97% and the specificity 83%. We conclude that immunocytological examination of urinary sediments in renal allograft recipients can be a valuable new tool in discriminating acute interstitial rejection from other causes of deteriorating graft function.