Untitled - Roche Trasplantes

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EARLY DIAGNOSIS OF CHRONIC ALLOGRAFT NEPHROPATHY BY MEANS OF PROTOCOL BIOPSIES Table I. Inclusion and exclusion criteria for protocol needle core biopsy. Inclusion criteria Deceased donor kidney allograft Informed consent Approved clinical trial or standard clinical practice Ultrasound examination available Skilled biopsy operator Exclusion criteria Bleeding disorder Use of anticoagulants including heparin, warfarin and aspirin Anatomical variation of graft position (e.g., overlying bowel) Anatomical variation of graft (e.g., arterio-venous malformation) Urinary obstruction Requirement for sedation to undertake biopsy Previous complication from biopsy To undertake protocol biopsy all of the inclusion criteria must be met and none of the exclusion criteria can be met. ones. Early and mild hyalinosis of the arterioles thus depends upon sampling sufficient arterioles and on hitting one with hyalinosis. Severe cellular ejection on the other hand is a diffuse process that can be seen throughout the kidney and can even be reliably implied on a section of medulla rather than cortex. The best study of reproducibility of the Banff schema was undertaken by Furness et al. (11). The histologists eye is clearly quite inconsistent when assessing the area of involvement of a biopsy and may miss rare events such as occasional lymphocyte invasion of a tubule. The exact grading of tubulitis may thus be inaccurate and when missed may lead to change in the overall diagnosis of rejection status. Individual pathologists appear to be more consistent internally than when compared with each other, and in the Furness study remained rather resistant to change of their readings despite feedback on their results relative to the mean. Comparison of results between two centres found reasonable agreement for acute rejection diagnoses in another study (12) with a kappa statistic of 0.77 for agreement on the diagnosis of acute rejection. Veronese demonstrated similar levels of agreement for acute rejection (0.47 – 0.72) but borderline rejection and fine grading of borderline rejection and individual Banff quantifiers was not so good (13). 15
BIOPSIA DE PROTOCOLO EN EL TRASPLANTE RENAL A recent analysis of the reproducibility of the reading of arteriolar hyalinosis demonstrates the problem nicely (14). In this study the authors compared two protocols for reading –the standard Banff schema and a new schema developed by Mihatsch. The reproducibility of the new schema was better than the standard Banff schema (kappa statistic 0.67 versus 0.52 comparing 45 biopsies from 38 patients), but the information derived from the readings was less informative. In the new schema, reproducibility was improved through reduction of the frequency with which intermediate scoring grades were used. The number of times when scores of 1 and 2 were used dropped from 64 using Banff to 24 with the new system. This meant that biopsies were scored as 0 or 3 most of the time, which is little better than a binary decision of present/absent. The essence of the problem is thus to find the balance between multiple grades of distinction for a given event such as tubulitis or tubular atrophy, which extracts maximum amounts of information from the biopsy, and simple grading systems which are highly reproducible but uninformative. The compromise that is represented by the current Banff schema, does at least have widespread application across transplant programs and through many clinical trials. It is important to recognize that it remains limited by the degree of reproducibility at the margins and could suffer further refinement with benefit. The areas of contention remain, for example, the relevance of cellular infiltrate in areas of fibrosis. The current schema requires these to be ignored, but that leads to the potential for variability in interpretation of exactly what constitutes an area of fibrosis in which the infiltrate is to be ignored. Fortunately, the schema is under continuous revision and improvement, so it is reasonable to hold the view that, despite the areas of poor reproducibility, the Banff schema for the interpretation of renal allograft pathology is the best that we have available. DEFINITIONS AND A MODEL OF CAN Understanding the complexity of the entity of chronic allograft nephropathy (CAN) has taken many years, since unlike acute rejection, it cannot be easily identified clinically, is multifactorial in origin and evolves over years and not days or hours. The reliability and sensitivity of serum creatinine measurement contributed substantially to the ability to diagnose and treat acute rejection in the early years of transplantation and is still one of the most reliable tools that we use in the clinic to identify patients in need of further investigation and change in management during the first few weeks after a renal transplant. Since the serum creatinine is also a fairly reliable indicator of chronic graft failure, as demonstrated by studies examining creatinine at one year as a predictor of graft loss, it has been natural to assume that monitoring the serum creatinine will identify grafts at risk from chronic graft failure and CAN. Experience has, however, taught us that this strategy does not, on the whole, allow identification of CAN at a stage when intervention can substantially alter the course of events. It is central to the understanding of CAN to realise why this is the case. It is also central to any strategies that might be effective in the 16
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