Background: Various morphologic indices for the evaluation of renal biopsies in lupus nephritis have been developed, of which the most successful have been the NIH Activity Index (AI) and Chronicity Index (CI). We wished to develop a biopsy index from standard light and immunofluorescence (IF) material that would correlate yet more closely with clinical and outcome parameters than the current indices, and be applicable to both treated and untreated cases.
Methods: A cohort of 71 patients with lupus nephritis who had initial renal biopsies (Bx1) with systematic second biopsies (Bx2) at six months after induction therapy was studied, with a large number of light microscopic and IF variables evaluated. These were examined statistically to choose the combinations of variables with the highest overall correlations with clinical and outcome parameters.
Results: The adopted biopsy index comprised four elements: Glomerular Activity Index (GAI), a modification of the standard AI with the addition of glomerular monocytes and elimination of interstitial inflammation; Tubulointerstitial Activity Index (TIAI), evaluating several tubular epithelial and inflammatory components, including interstitial inflammation, but excluding tubular atrophy; Chronic Lesions Index, a modification of the standard CI, with the addition of glomerular scars; IF Index (IFI), a semiquantitative index of IF staining for six standard antisera for glomerular capillary, mesangial, tubulointerstitial, and vascular elements. The Biopsy Index showed a statistically higher correlation with clinical and outcome parameters than the NIH AI (P = 0.0170), the NIH CI (P = 0.0009), or their combination (P = 0.0444). At Bx1, comparisons between correlation coefficients for the appropriate AI or CI value and for the Biopsy Index, were: anti-DNA antibodies (0.30 vs. 045), serum creatinine (SCr; 0.33 vs. 0.48), proteinuria (0.22 vs. 0.36), hemoglobin (-0.21 vs. -0.45), and final renal function (0.22 vs. 0.40). Spearman rank correlations showed similar superiority for outcome parameters: doubling of SCr (0.1810 vs. 0.3018) and end-stage renal disease (0.0529 vs. 0.1925). The same improvement of correlations was seen at Bx2 for most parameters, particularly doubling of SCr (0.2716 vs. 0.4753).
Conclusions: The Biopsy Index and/or its components show better correlations with clinical and outcome parameters than the standard AI and CI and other similar indices.