Assessment of renal microcirculation in biopsy-proven tubulointerstitial nephritis in patients with and without glomerular disease: the role of resistive index.

Abstract

Renal resistive index (RRI) measured by Doppler sonography is a marker of microvascular status and it is associated with changes in renal function. Aim of the study was to assess RRI in biopsy-proven tubulointerstitial nephritis (TIN) in patients with and without glomerular disease. 132 consecutive patients underwent to native renal biopsy with diagnosis of isolated TIN or in association with glomerulonephritis. Estimated glomerular filtration rate (eGFR), 24-hour urinary protein excretion and renal ecocolorDoppler ultrasonography with RRI assessment were performed at time of enrollment. Patients with isolated-TIN had significantly higher RRI than both patients with non-immunoglobulin A glomerulonephritis (non-IgA-TIN) [0.73 (0.68-0.77) vs 0.64 (0.60-0.67), p<0.001] and patients with IgA nephropathy (IgAN) [0.73 (0.68-0.77) vs 0.66 (0.60-0.71), p<0.01]. Patients with isolated-TIN had mainly RRI≥0.70 (n=15, 65.2%) with the respect to patients with non-IgA-TIN (n=7, 12.3%) and patients with IgAN (n=17, 32.7%). A negative linear correlation was found between RRI and hemoglobin (r=0.233, p<0.01) and between RRI and eGFR (r=0.537, p<0.001). Tubulointerstitial damage is the most accurate histological lesion that correlates with eGFR and renal impairment. RRI can be a useful parameter to detect tubulointerstitial lesions.