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We read ACP Best Practice No 160 “Renal biopsy specimens” with interest.1 Dr Furness rightly avoids providing a list of specific procedures to follow because, as he points out “there is a need to assess each case on its merits, rather than following rigid rules”. It is clear from an audit of handling of renal biopsies in the UK, performed in 1999, that standard operative procedures vary widely, and that many laboratories fall short of “best practice”. A probable reason for this is that there is very little hard evidence to support any specific recommendations. In the UK audit, a questionnaire was circulated to all members of the UK Renal Pathology Group and returns were received from 50% of the 54 laboratories represented. It is interesting to compare current practices with Dr Furness's guidelines.
Dr Furness recommended that all specimens should be examined in the biopsy room for adequacy, using a dissecting microscope. However, in only 15% of units is this performed as routine. Failure to confirm the presence of renal cortex in the specimen would be expected to increase dramatically the proportion of inadequate biopsies. This was not the experience in Manchester, however, where in 1994, as a result of staff shortages, the practice of sending an MLSO to attend every biopsy procedure was stopped.2 In Oxford, the histopathology laboratory is on a different site to the renal and transplant units; neither an MLSO nor a pathologist attends biopsies, as was once the case. Furthermore, what constitutes an adequate specimen is difficult to define and to some extent depends on the nature of the pathology. More tissue is required to detect focal than diffuse lesions.3 This has been demonstrated in renal allograft biopsies; in the validation study of the CCTT classification of allograft pathology, those biopsies showing acute vascular rejection contained the diagnostic arteritic lesion in only one of two cores taken in 82% of cases.4 In the UK audit, it was found that the number of cores of renal tissue routinely taken varied from one to four in different centres. Dr Furness recommends that division of the specimen should be done within minutes of the biopsy being taken, to avoid artefactual ultrastructural changes. Although subtle subcellular changes do develop if fixation is delayed, for routine diagnostic electron microscopy (EM) rapidity of fixation is much less crucial. Formaldehyde fixation alone may produce excellent ultrastructural detail and is the fixative of choice for EM in some laboratories. Occasionally, we have received specimens that have been stored unfixed in transport gel for two days, and found preservation to be adequate for the purposes of diagnostic EM.2
There is also variation in the immunohistochemical techniques used when handling native renal biopsies. A frozen sample for immunofluorescence (IF) is taken routinely in 81% of laboratories; the remaining 19% rely entirely on immunoperoxidase (IP) stains performed on paraffin wax embedded sections. This, in part, reflects varying success in achieving reliable results with IP for immunoglobulins and complement. In the case of early transplant biopsies, only 30% of laboratories routinely take frozen tissue for IF. In those that do, it is often taken for research purposes rather than for patient management. Similarly, most laboratories (88%) routinely take tissue for EM from native renal biopsies. Because some of the most common renal diseases, such as thin membrane nephropathy, can only be diagnosed ultrastructurally, those laboratories that do not take tissue for EM are certainly falling short of “minimum adequate practice”. Although it may be “best practice” to perform EM in all cases,5 it is probably sufficient to store this tissue as a resin block and only perform EM if the light microscopy is non-diagnostic.6 In many instances, EM will not influence patient management and the “minimum adequate practice” would, therefore, be to consider each case on its own merits and perform further investigations only if necessary. At present, EM does not have a clearly defined role in the assessment of early transplant biopsies and the UK audit found that only 38% of laboratories routinely take tissue for EM from these specimens.
The choice of which special investigations are performed should, at least in part, be determined by our clinical colleagues. Nephrologists differ widely in how aggressive they are in investigating patients with asymptomatic renal disease, such as those presenting with microscopic haematuria detected at a routine health check. In some centres a biopsy will only be performed if it is likely to affect management of that patient; in others, biopsy practice is partly driven by research interests. Equally, the information required from the pathologist will depend on its potential clinical value. For example, providing a measure of the severity of chronic tubulointerstitial injury in a patient with membranous nephropathy is of far more value to the nephrologist than knowing the glomerular disease stage, as defined by ultrastructural appearances.
In the UK audit, the number of paraffin wax sections routinely cut for native renal biopsies varied greatly—from two sections on two slides to 70 sections on 10 slides—again reflecting a lack of evidence base. In his article, Dr Furness indicated that the number of sections that should be cut and examined depends on the nature of the question. A renal biopsy standard operative procedure should, however, include examination of sufficient sections to enable the diagnosis of conditions in which the pathology is usually focal. In the case of primary focal segmental glomerulosclerosis, this is considerably in excess of two. For renal transplant biopsies, the Banff classification7 recommends that at least three haematoxylin and eosin (H&E) and three periodic acid Schiff or methenamine silver stained sections should be examined. The rationale behind this is that the diagnostic lesions of acute rejection—tubulitis and arteritis—are often focal. A recent review of transplant biopsies in Manchester concluded that one third of diagnoses of acute vascular rejection would be missed if only one, rather than three, H&E sections were examined (GP McCarthy, ISD Roberts, 2000, unpublished data).
All laboratories that handle renal biopsies should review their standard procedures, particularly if they do not conform to Dr Furness's guidelines or “usual practice”, as indicated by the UK Renal Pathology Group audit. As the diagnostic questions asked by nephrologists change and new techniques emerge, procedures will inevitably require updating, but we will need to provide the evidence that any changes introduced are of demonstrable benefit to patient management.
I am grateful for the opportunity to respond to the letter of Drs Roberts and Davies on the ACP Best Practice article “Renal biopsy specimens”,1 although they say very little with which I disagree. Most of their points of difference relate to “current practice” or “minimum adequate practice” rather than “best practice”. For example, the observation that electron microscopy (EM) can provide useful information even if fixation is delayed for a day or more is interesting and useful information. It supplements my observation that tissue from the paraffin wax block can be reprocessed for EM, but it does not alter the fact that best practice is to get the tissue fixed quickly!
The UK audit that they describe is a welcome update of a similar study that we performed in 1995,2 and which influenced the development of the ACP guidelines.
There is one small point where I think that Roberts and Davies misrepresent my suggestions. In their discussion of identifying and dividing the sample under a dissecting microscope, they imply that this has to be done by a pathologist or an MISO. We have found that nephrologists and radiologists can identify renal cortex and divide the biopsy appropriately with only minimal training. Again, rapid division is best practice; taking a bit longer is probably quite adequate in most circumstances, but (for example) in the future a delay will probably invalidate studies of gene expression.
Apart from these rather trivial quibbles I welcome Roberts and Davies's contribution to the discussion.
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