Nephrology Dialysis Transplantation, Vol 13, Issue 1 165-172, Copyright © 1998 by Oxford University Press
H Wang, C Kjellstrand, S Cockfield and K Solez
Introduction: The minimal specimen size necessary for
accurate interpretation of renal biopsy has not been identified. We
attempted such a determination by three different analyses of a collection
of biopsies performed in renal transplants. Methods:
First, we studied the influence of three lesions (glomerulosclerosis,
arteriolar hyalinosis, interstitial fibrosis/tubular atrophy) in 199
baseline biopsies, obtained at time of transplantation, on transplant
outcome. Secondly, we compared the results from the three lesions, in
baseline biopsy with those from 114 subsequent core biopsies in the same
patients. Thirdly, we compared the two baseline biopsies obtained in 118
paired kidneys in cadaver transplantation where both kidneys were used.
Results: For statistically significant prediction of
outcome from glomerulosclerosis, we found that a specimen containing at
least 25 glomeruli was needed in the baseline biopsy. Arteriolar hyalinosis
predicted outcome independent of sample size, but became less important
than percentage glomerulosclerosis in predicting outcome if only samples
containing more than 25 glomeruli were considered. Interstitial
fibrosis/tubular atrophy did not predict the outcome for a kidney,
independent of sample size. When comparing baseline with subsequent core
biopsies, or with paired baseline biopsies, at least 14 glomeruli were
necessary to allow even moderate reproducibility of glomerulosclerosis
(Cohen's kappa <0.25) and to allow statistical significance (P
<0.05). The reproducibility of arteriolar hyalinosis was not
dependent on sample size but was reproducible in 80% of paired baseline
biopsies, and in 67% of the comparison of the baseline with core biopsy.
Both precision and significance was lost if sample numbers were reduced by
including only larger samples. There was no reproducibility I any study of
interstitial fibrosis/tubular atrophy when comparing either baseline with
subsequent biopsy, or paired baseline biopsies.
Summary: Much larger biopsy samples are necessary than
has generally been assumed in order for glomerulosclerosis rates to be
reproducible or predictive of outcome. Arteriolar hylainosis is
prognostically important and shows good reproducibility independent of
sample size. Interstitial fibrosis/tubular atrophy appear useless as
predictors, being of no prognostic importance and lacking reproducibility.
Our finding clarifies some of the discrepancies found by different
investigators regarding the importance of renal biopsy in predicting
prognosis. Preliminary, our data indicate that samples containing fewer
than 25 glomeruli are unreliable in determining outcome based on
glomerulosclerosis. The importance of our findings which are based only on
chronic lesions, with respect to acute changes, is unknown. Key
words: sample size; renal biopsy; prognosis; transplant outcome;
reproducibility
ORIGINAL ARTICLES
On the influence of sample size on the prognostic accuracy and reproducibility of renal transplant biopsy
Department of Pathology and Medicine, Faculty of Medicine, University of Alberta, Canada; Corresponding author at: VP Medical Affairs Aksys Ltd, Two Marriott Drive, Lincolnshire, IL 60069, USA
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