Computer-assisted measurement of glomerular size in IgA nephropathy: Practical issues and correlation with the Oxford Classification.

Background&objectives: Glomerular size has been demonstrated as an independent prognostic marker in IgA nephropathy. Using digital pathology, this study aims to determine reproducibility of GD measurement, defining minimum number of glomeruli required for accurate measurement, and correlating GD with MEST-C scores. Method(s): The diameter of all non-sclerosed glomeruli from renal biopsies of 420 patients with IgA nephropathy was measured independently by 3 pathologists, using the ruler device on Aperio ImageScope software. Inter-observer and intra-observer variability was then assessed using interclass correlation coefficient (ICC). Mean and maximum GD were correlated with Oxford Classification MEST- C scores, using the independent samples T test. Result(s): There was excellent interobserver (between 3 pathologists) and intra-observer (one pathologist measuring 2 levels from the same biopsy) correlation with ICC of >0.9. Accuracy of measurement ofmaximumand mean GD increased with number of glomeruli measured, levelling off between 12-15 non-sclerosed glomeruli. T score was the only MEST-C variable to significantly correlate with glomerular diameter. Conclusion(s): Use of the ruler device on digital slide viewing software provides a rapid and reproducible estimate of glomerular diameter. Greater than 12 non-sclerosed glomeruli are required to provide an accurate measurement of the glomerular diameter. Glomerulomegaly results from adaptive changes associated with hyperfiltration that is in part determined by the severity of chronic renal injury, reflected by correlation of GD with Oxford Classification T score.