The Whitaker Test

The Whitaker test, also known as the ureteral perfusion challenge, is an invasive provocative maneuver used to differentiate obstructive from non-obstructive uropathy in the presence of a dilated collecting system, for example, in

• Patients with dilated renal pelves and suspected ureteropelvic obstruction,
• Patients with dilated ureters and concern for obstruction,
• Patients following treatment for collecting system obstruction,
• Renal transplant patients with hydronephrosis, and
• Patients with urinary obstruction who do not demonstrate dilatation of the collecting system.

Fluid is instilled into the renal pelvis starting at 5 mL/min for up to 5 minutes and the pressure gradient between the kidney and bladder is measured. A normal absolute renal pelvis pressure is less than 25 mm H2O. If the absolute pressure is above 30 mm H2O or an abnormally high resting gradient is detected, we have the diagnosis and no provocative challenge is needed.

If the absolute pressure is normal, the test continues by measuring the pressure gradient between the renal pelvis and urinary bladder during instillation of saline mixed with contrast. Contrast is used in the instillate to visualize the collecting system and possible site of obstruction.

A normal pressure gradient is less than 15 mm H2O at maximal fluid challenge (see below). A pressure gradient above 22 is diagnostic of obstruction. Pressure gradients between 15 and 22 are indeterminate. Higher infusion rates (up to 20 mL/min) can help in these cases. Negative or indeterminate cases can also be repeated with a distended bladder or using different patient positioning.

The renal pelvis pressure is measured while it is being perfused by inserting a second (transducer) needle (two-needle technique) or by inserting the transducer needle after withdrawing the infusion needle (one-needle technique). The bladder pressure is measured via Foley catheter.