Duplex Doppler ultrasound in the diagnosis of acute renal allograft rejection.

As renal transplantation becomes more commonplace and successful, there is an increasing demand for non-invasive methods of studying possible complications. One hundred and fifty-four duplex Doppler sonography scans were performed in 38 patients within 52 days of receiving a renal allograft. Renal vascular impedance was estimated in the intrarenal arteries by calculating the resistive index ([peak systolic frequency shift--lowest diastolic frequency shift]/peak systolic frequency shift). A resistive index of greater than 0.80 was very suggestive of rejection (positive predictive value 82%); with a value of less than 0.70 rejection was unlikely (negative predictive value, 98%).