Does Renal Urography Require Iodinated Contrast?
Yes, intravenous urography (IVU) requires intravenous administration of iodinated contrast material to visualize the urinary collecting system and evaluate renal excretory function. 1
How IVU Works
- IVU involves injecting iodinated contrast material intravenously, which is then filtered by the kidneys and excreted through the collecting system, allowing radiographic visualization of the renal pelvis, ureters, and bladder 1, 2
- The contrast agent opacifies the urinary tract structures on sequential radiographic images taken at timed intervals after injection 2
- Without contrast administration, standard radiography (KUB) can only visualize calcifications and soft tissue shadows, not the functional collecting system 1
Current Clinical Role
- IVU has been almost completely replaced by CT urography in modern practice 1, 2
- IVU should be used primarily in kidney injuries discovered during surgery in unstable patients before opening retroperitoneal hematoma, or when CT is unavailable in low-resource settings 1
- The false negative rate of IVU ranges between 37-75%, making it unreliable for many diagnostic purposes 1
- IVU is considered an unreliable test for ureteral injury evaluation with false negatives up to 60% 1
Contrast-Related Risks
- Iodinated contrast carries a well-known risk of acute renal failure, especially in patients with preexisting renal impairment 1
- In patients with renal insufficiency (serum creatinine ≥2 mg/dL), the incidence of renal impairment after IVU is 55%, compared to 15% in those without renal insufficiency 3
- High blood pressure is an additional risk factor, with 28.6% of hypertensive patients experiencing renal impairment versus 10.5% of normotensive patients 3
- Most cases of contrast-induced renal impairment are mild and reversible, with renal function returning to baseline within a mean of 12 days 3
- The risks of severe contrast reactions using American College of Radiology criteria are extremely low 1
Modern Alternatives
- Multi-phasic CT urography (CTU) with intravenous contrast has the highest sensitivity and specificity for imaging the upper urinary tracts and is now the imaging procedure of choice 1
- For patients with contraindications to iodinated contrast (renal insufficiency, contrast allergy, pregnancy), MR urography with or without IV gadolinium contrast is an acceptable alternative 1
- Ultrasound combined with plain radiography can be used but presents significant risks for missed diagnoses compared to CTU 1
Key Clinical Pitfall
The most important pitfall is attempting IVU in patients with compromised renal function without considering the nephrotoxicity risk. Always assess baseline renal function before administering iodinated contrast, and consider alternative imaging modalities (MRU, ultrasound) in high-risk patients 1, 3.