Why rejections are not biopsy proven: frequency and reasons

Rejection still has a fundamental impact on patient and graft survivals after renal transplantation. Published studies vary widely in their reporting of biopsy-proven acute rejection (BPAR) and non-BPAR rates. We undertook a systematic search of existing publications for reasons explaining this difference. Additionally, we analyzed our own population, which has a clearly defined biopsy strategy, to further investigate the rate of non-BPAR in routine clinical practice.

From large, multicenter, randomized, controlled trials investigating immunosuppressive regimens in de novo kidney transplant recipients, we extracted the rates of all reported rejections ("total" rate) versus BPAR. Non-BPAR was defined as the difference between "total" and BPAR. Additional analyses were performed for potential influencing factors, such as year of publication, number, and mean age of patients recruited and impact factor of the journal at the time of publication. We scanned all de novo adult patients undergoing kidney transplantation in our center between 1996 and 2004 for rejection episodes during the first year.

The median rate of non-BPAR within the first year in 27 papers was 7% (range, 0%- 16.9%). Similarly, the relative proportion of non-BPAR showed large differences. We could not identify potential influencing factors to explain the large variability. Among our population, 136/365 patients (37.3%) experienced acute rejection episodes, with BPAR diagnosed in 90/365 patients (24.7%), yielding an absolute 12.6% rate of non-BPAR.

Even centers with a well-defined biopsy strategy show a substantial proportion of non-BPAR episodes. Therefore, complete reporting of both BPAR and non-BPAR is important for the proper interpretation of study results.