Development and validation of a diagnostic nomogram to evaluate tubular atrophy/interstitial fibrosis of IgA nephropathy

Abstract

Background: IgA nephropathy (IgAN) is a cause of chronic kidney disease (CKD). Tubular atrophy/interstitial fibrosis is associated with IgAN prognosis. However, simple tools for predicting pathological lesions of IgAN remain limited. Our objective was to develop a tool for evaluating tubular atrophy/interstitial fibrosis in patients with IgAN. Methods: In this cross-sectional study, 410 biopsy-verified IgAN patients were included. The factors associated with the incident interstitial fibrosis or tubular atrophy in IgAN were confirmed by using logistic regression analysis. A nomogram was developed using logistic regression coefficients to evaluate tubular atrophy or interstitial fibrosis. Receiver operating characteristic curves (ROC) and calibration curves were used to determine the discriminative ability and predictive accuracy of the nomogram. Results: In this study, the IgAN patients with tubular atrophy or interstitial fibrosis were older and had a higher percentage of males, hypertension and urinary protein excretion (UPE), with high levels of serum cystatin C, serum creatinine, high-sensitivity C-reactive protein and serum C4. The eGFRcr-cys equation calculated using serum creatinine, cystatin C and UPE were considered independent influencing factors of tubular atrophy or interstitial fibrosis in patients with IgAN. Furthermore, the nomogram demonstrated good discrimination (AUC: 0.87, 95% CI 0.81 to 0.93) and calibration in the validation cohort. Conclusion: The eGFRcr-cys and UPE are associated with tubular atrophy or interstitial fibrosis in patients with IgAN. Diagnostic nomogram can predict tubular atrophy or interstitial fibrosis in IgAN.

Keywords: IgA nephropathy; estimated glomerular filtration rate; nomogram; pathological change.

Figure 1

ORs for tubular atrophy/interstitial fibrosis associated with eGFRcr-cys and UPE. ORs are from a multivariable-adjusted model including hypertension, serum albumin, serum IgG, serum C4, eGFRcr-cys and UPE. Boxes in the graph represent the OR and lines/arrows represent the 95% CI.

Figure 2

Diagnostic nomogram. To use the nomogram, draw a line perpendicular from the corresponding axis of each risk factor until it reaches the top line labeled “Points”. Sum up the number of points for all risk factors then draw a line descending from the axis labeled “Total points” until it determined the probabilities of tubular atrophy/interstitial fibrosis.

Figure 3

ROC curves of the nomogram. AUC: area under the curve.

Figure 4

The calibration curves of the nomogram for predicting the T1/2 lesions of IgAN patients at (A) in the derivation cohort and (B) in the validation cohort. The X-axis represents the nomogram-predicted probability of diagnosis, and the Y-axis represents the actual probability estimated with the logistic regression methods.