Duplex Doppler evaluation of native kidney dysfunction: obstructive and nonobstructive disease.

Intrarenal duplex Doppler sonography can provide physiologic information reflecting the status of renal vascular resistance. Available data suggest 0.70 as a reasonable upper limit for normal intrarenal resistive index. Complete or significant partial urinary obstruction produces a prompt elevation in the resistive index that is not produced by purely nonobstructive dilatation; hence, Doppler imaging appears useful in evaluating the dilated, possibly obstructed kidney. In addition, intrarenal Doppler sonography may prove to be a useful noninvasive test to suggest the significance of partial obstruction. Nonobstructive renal disease also can cause elevation of the resistive index. Recent biopsy series, although correlating certain pathologic findings with resistive index, also indicate that renal Doppler sonography is not sensitive or specific enough to replace renal biopsy. To date, Doppler study of renal medical disease has proved most useful in two types of applications: monitoring of patients with renal disease known to produce resistive index elevation and differentiating between renal diseases where one produces more marked Doppler changes than the other. Resistive index is clearly not identical to creatinine level; in some instances the resistive index may provide unique noninvasive information regarding renal arterial resistance not available from conventional laboratory parameters.