When is a computed tomography (CT) scan with contrast, specifically a non-ionic, low-osmolar contrast agent such as iodixanol (iodixanol) or iohexol (iohexol), indicated for a patient with suspected cancer, abdominal pain, or trauma, and what are the considerations for patients with impaired renal function?

When to Get CT Scan with Contrast

CT with intravenous contrast is indicated for trauma (blunt or penetrating), suspected cancer, acute abdominal pain, mesenteric ischemia, and retroperitoneal bleeding, but should be avoided in patients with GFR <30 mL/min/1.73m² unless the diagnostic benefit outweighs the risk of contrast-induced nephropathy. 1

Trauma Indications

For blunt trauma, CT abdomen and pelvis with IV contrast in the portal venous phase (70 seconds post-injection) is the gold standard and should be obtained in hemodynamically stable patients. 1

• Noncontrast CT should be avoided if there is no contraindication to IV contrast because of lower sensitivity for detecting both visceral organ and vascular injuries 1
• Arterial and venous phases (20-30s and 70-80s delay) allow identification of almost all injuries, with a 5-minute delayed phase added selectively for suspected urogenital injuries 1
• CT identifies high-risk criteria for non-operative management failure including contrast blush, perirenal hematoma >3.5 cm, and medial laceration with urinary extravasation 1
• Oral contrast is not recommended as it does not alter sensitivity or specificity and delays diagnosis 1

Acute Abdominal Pain and Suspected Infection

CT abdomen and pelvis with IV contrast is usually appropriate as initial imaging for patients with suspected sepsis and acute abdominal pain. 1

• For mesenteric ischemia, CT angiography (CTA) with both arterial and portal venous phases is preferred over standard CT with venous phase alone, as arterial phase influenced care in 19% of patients 1
• CTA has sensitivity and specificity as high as 93-100% for acute mesenteric ischemia diagnosis and can improve patient survival 1
• CT with IV contrast can assess nonvascular findings and major arterial lesions, but lack of arterial phase may lead to suboptimal evaluation compared to CTA 1

Cancer Evaluation

Contrast-enhanced CT provides superior diagnostic information for cancer detection and characterization compared to non-contrast studies. 2

• Contrast enhancement allows better visualization of subtle abnormalities and helps identify complications 2
• The diagnostic accuracy of contrast-enhanced CT significantly exceeds that of non-contrast CT or alternative imaging modalities 2

Renal Impairment Considerations

The decision to use contrast must be based on current GFR, with patients having GFR <60 mL/min at increased risk for contrast-induced nephropathy. 2, 3, 4

GFR >60 mL/min/1.73m²

• Contrast can be administered with minimal risk 2
• Standard protocols apply without special precautions 2

GFR 30-60 mL/min/1.73m² (Stage 3 CKD)

• Proceed with contrast if the clinical question cannot be answered with alternative imaging and the information is critical for patient management 2, 4
• Implement mandatory precautions:
  • Adequate pre-procedural hydration with isotonic saline (1 mL/kg/hour starting 12 hours before and continuing 24 hours after) 4
  • Use low-osmolar (iohexol) or iso-osmolar (iodixanol) contrast agents only 2, 4, 5
  • Minimize contrast volume to the lowest necessary dose 2, 4, 5
  • Hold NSAIDs, metformin (for 48 hours after), and aminoglycosides 4
• Monitor serum creatinine at 48-72 hours post-procedure 4

GFR <30 mL/min/1.73m²

• Avoid contrast-enhanced CT if possible and consider alternative imaging (MRI without gadolinium, ultrasound) 1, 3
• CT urography is not recommended in patients with renal failure 1, 3
• If contrast is absolutely necessary for life-threatening conditions (ST-elevation MI, aortic dissection, pulmonary embolism), proceed immediately with all protective measures 4
• In severe renal impairment, plasma half-life increases from 2.1 hours to 23 hours, and contrast enhancement time extends to at least 24 hours 5

Specific Clinical Scenarios

Retroperitoneal Bleeding

• CTA abdomen and pelvis is appropriate for initial evaluation, detecting bleeding rates as low as 0.3 mL/min with sensitivity of 59.5% 1
• Noncontrast CT can expeditiously confirm or exclude bleeding, especially helpful in patients with compromised renal function 1

Hydronephrosis with Unknown Cause

• CT abdomen and pelvis with IV contrast may be useful in symptomatic patients, particularly with renal colic and moderate to severe hydronephrosis 1
• More comprehensive evaluation can often be achieved with CT urography, MR urography, or renal scintigraphy 1

Renal Transplant Dysfunction

• The utilization of CT abdomen and pelvis with contrast should be considered in conjunction with risks of nephrotoxicity from iodinated contrast 1
• CTA can provide detailed anatomic depiction of vascular complications (renal artery stenosis, renal vein thrombosis, pseudoaneurysm) prior to percutaneous angiography 1

Common Pitfalls to Avoid

• Do not use prophylactic hemodialysis or hemofiltration for contrast removal 4
• Do not rely on oral hydration alone in high-risk patients 4
• Do not delay urgent life-saving procedures due to fear of contrast-induced acute kidney injury 4
• Failing to check current renal function before administering contrast 2, 4
• Not providing adequate hydration, which is the single most important preventive measure 4
• Using high-osmolar contrast agents in patients with renal impairment 4
• Administering excessive contrast volume when a lower dose would be sufficient 2

Contrast Agent Selection

Use non-ionic, low-osmolar (iohexol) or iso-osmolar (iodixanol) contrast agents, as they may be associated with lower incidence of contrast-induced nephropathy. 4, 5

• Iodixanol provides comparable image quality to iohexol with lower incidence of adverse events (0.7% immediate events vs 2% with iohexol) 6
• Both agents have low nephrotoxicity profiles in routine examinations, especially in elderly or high-risk patients 7
• The risk of contrast-induced nephropathy is significantly higher in patients with underlying renal insufficiency (9.0% developed contrast nephropathy) but should not serve as absolute contraindication when contrasted CT provides valuable information for life-threatening clinical questions 8