A resistive index (RI) greater than 0.70 in a kidney is indicative of early:

A resistive index (RI) greater than 0.70 in a kidney is indicative of early obstructive hydronephrosis due to the renal parenchyma's response to increased pressure.

In cases of obstructive hydronephrosis, the elevated resistance to blood flow reflects the compromised perfusion caused by the obstruction of urine flow. This increased resistance can lead to changes in vascular dynamics, where renal arterial resistance rises. As the obstruction progresses and the kidney becomes increasingly distended with urine, the RI reflects that change by exceeding the normal threshold, which is typically around 0.70.

Since the resistive index increases in the setting of renal obstruction, it serves as an important diagnostic parameter. Evaluating the RI can aid in determining the severity of the obstruction and the need for potential intervention to restore normal urinary flow. This understanding is critical for sonographers and clinicians when assessing kidney health and diagnosing conditions related to urinary tract obstruction.