Abstract
RATIONALE & OBJECTIVE: The number of glomeruli is often used to determine the adequacy of a kidney biopsy (eg, at least 10 glomeruli). It is often assumed that biopsy specimens with limited amounts of cortex are too imprecise for detection of focal pathology. STUDY DESIGN: Clinical-pathologic correlation (cross-sectional). SETTING & PARTICIPANTS: Living kidney donors who underwent a needle core biopsy of their kidney at the time of donation. EXPOSURE: The amount of cortex biopsied as determined by either the number of glomeruli or area of cortex on histology. OUTCOME: The percentage of globally sclerotic glomeruli, density of interstitial fibrosis foci, and severity of arteriosclerosis were determined. ANALYTICAL APPROACH: A beta-binomial model assessed how the mean percentage of globally sclerotic glomeruli and patient variability in percentage of globally sclerotic glomeruli differed with the number of glomeruli on the biopsy specimen. Additional models assessed the association of interstitial fibrosis and arteriosclerosis with number of glomeruli. RESULTS: There were 2,915 kidney donors studied. Fewer glomeruli on the biopsy specimen associated with higher mean percentage of globally sclerotic glomeruli and higher patient variability in percentage of globally sclerotic glomeruli. Smaller cortical volume on imaging correlated with both less cortex on biopsy and higher percentage of globally sclerotic glomeruli. Based on a statistical simulation, the probability of patient percentage of globally sclerotic glomeruli ≥ 10% if the biopsy percentage of globally sclerotic glomeruli is ≥10% (positive predictive value) was 45% with 1 to 9 glomeruli versus 31% with 10 or more glomeruli; the negative predictive value was 91% versus 98%. Fewer glomeruli also associated with more interstitial fibrosis and arteriosclerosis. LIMITATIONS: The study was limited to living kidney donors. Patient variability in percentage of globally sclerotic glomeruli was based on a statistical model because multiple biopsy specimens per patient were not available. CONCLUSIONS: The amount of cortex on a needle core biopsy is not completely random. Chronic changes from loss of cortex contribute to low amounts of cortex on a kidney biopsy specimen.