Renal resistive index early detects chronic tubulointerstitial nephropathy in normo- and hypertensive patients

Background: We studied whether the measurement of intrarenal vascular resistance by Doppler ultrasonography, capable of investigating renal interstitial compartment, allows the early detection of chronic tubulointerstitial nephropathy (TIN). Methods: 30 normotensive and 28 hypertensive (I-II OMS) patients with a clinical history suggestive of chronic TIN and normal renal function were enrolled. 40 healthy volunteers served as controls. Patients were considered TIN-negative or TIN-positive after investigating tubular function by urine concentrating and acidification tests. Renal sonographic parameters and renal resistive index (RRI) were obtained by duplex scanner. Glomerular filtration rate/effective renal plasmatic flow ratio was investigated by sequential renal scintigraphy in TIN-negative and TIN-positive patients; ^99mTc-DMSA scintigraphy was also performed in TIN-positive patients. Results: RRI values of TIN-positive normotensive and hypertensive patients were significantly higher (p <0.01 for both) than those of TIN-negative patients and of controls. RRI values resulted to be linearly related to uricemia (r = 0.88, p <0.0001) only in normotensive patients. RRI values also resulted to be linearly related to filtration ratio values (r = 0.60, p <0.0001). ^99mTc-DMSA scintigraphy confirmed interstitial renal damage (grade 1 and 2). Conclusion: RRI measurement allows the early identification of both normotensive and hypertensive patients with chronic TIN and signs of tubular dysfunction, when renal function is still preserved.