Detection of chronic allograft nephropathy by quantitative doppler imaging.

Background: Chronic allograft nephropathy (CAN) is the major cause of graft loss, and early detection is desirable to avoid irreversible graft damage. We have evaluated a new technique of color Doppler quantification using Cineloop (Philips Medical Systems, Bothell, WA) imaging for noninvasive diagnosis of CAN.

Methods: Provisional normal ranges were defined by pilot study (n=13) and prospectively tested in stable recipients in whom CAN was independently quantified by contemporaneous histology (n=67), using the Banff schema.

Results: The maximal fractional area (MFA, systolic color pixels/total area) was 28.7+/-9.7% in normal subjects and reduced to 18.8+/-8.0% in grade 1 and 12.5+/-6.4% in grade 2 CAN (both P<0.001). The minimum color fractional area was reduced from 10.3+/-5.3% in normal subjects to 3.1+/-2.6% in grade 2 CAN (P<0.001), but was less useful. Distance from peripheral color pixels to capsule increased in CAN grade 2 versus 0 (6.0+/-1.6 vs. 3.9+/-1.0 mm, respectively; P<0.001). Calcineurin inhibitor nephrotoxicity reduced MFA (18.0+/-9.3 vs. 26.9+/-10.7%; P<0.001) and other dynamic measurements. Parenchymal damage exerted minimal effect on resistance index, mean variance, and peak Doppler velocity. MFA (cutoff<17.3%) can diagnose CAN (sensitivity 69%, specificity 88%, positive predictive value 86%) and severe CAN (sensitivity 87%, specificity 71%, negative predictive value 95%). Distance to capsule >5 mm was less sensitive (49%) but more specific (91% alone, and 97% combined with MFA).

Conclusions: In conclusion, quantitative Doppler ultrasound can reliably detect CAN and, although imperfect at correctly grading, allows recognition of significant tubulointerstitial damage for initiation of a confirmatory needle core biopsy.