When do you order a CT with contrast in patients with suspected cancer, infection, or trauma, considering age, GFR, and allergy history?

When to Order CT with Contrast

CT with intravenous contrast should be ordered when evaluating soft tissue pathology, vascular structures, infection, inflammation, or tumors, while non-contrast CT is preferred for calcifications, stones, bone structures, acute hemorrhage, and in patients with contraindications to contrast. 1

General Decision Framework

Order CT WITH Contrast for:

• Suspected infection or abscess - Contrast enhancement increases conspicuity of paraspinal soft tissue abnormalities, inflammation, and abscesses 2
• Suspected malignancy - Essential for detecting and characterizing tumors, with contrast improving visualization of pleural abnormalities and soft tissue masses 2, 1
• Vascular evaluation - Required for assessing vascular occlusions, pulmonary embolism, or aortopathy 2
• Inflammatory conditions - Helps identify areas of abnormal enhancement indicating active inflammation 1
• Solid organ injury in trauma - Portal venous phase imaging is most helpful for detecting liver, spleen, and kidney injuries 2

Order CT WITHOUT Contrast for:

• Suspected urolithiasis - Non-contrast CT has 97% sensitivity for kidney stones and is the gold standard 3, 4
• Acute head trauma or stroke - Non-contrast head CT is first-line to detect hemorrhage before considering thrombolysis 2, 5
• Bone evaluation - Preferred for assessing fractures, bone lesions, and matrix mineralization 2, 1
• Rib fractures in suspected abuse - More sensitive than radiography without requiring contrast 2
• Calcifications - Non-contrast optimally demonstrates calcium deposits 1

Clinical Context-Specific Recommendations

Suspected Spine Infection

• MRI spine without and with IV contrast is the gold standard (sensitivity 96%, specificity 94%) 2
• If MRI contraindicated or equivocal, use CT spine with IV contrast - the addition of contrast increases conspicuity of paraspinal soft tissue abnormalities and abscesses 2
• Non-contrast CT alone has low sensitivity (6%) for epidural abscess 2

Acute Mental Status Changes

• Non-contrast head CT is first-line in all patients to rapidly exclude hemorrhage 2
• Add contrast only if intracranial infection, tumor, or inflammatory pathology suspected after initial non-contrast scan 2
• Common practice: perform non-contrast screening CT, then follow with contrast-enhanced study or MRI if occult pathology suspected 2

Suspected Malignancy

• CT chest with IV contrast is recommended for suspected malignant pleural effusion, acquiring images 60 seconds after contrast bolus to improve visualization 2
• CT abdomen/pelvis with IV contrast for staging colon cancer - contrast should be IV and oral when feasible 2
• Consider abdominal/pelvic MRI with contrast plus non-contrast chest CT if CT with IV contrast is contraindicated 2

Trauma Scenarios

Blunt Abdominal Trauma:

• IV contrast is essential for solid organ injury detection 2, 1
• Oral contrast is NOT necessary - studies show no diagnostic advantage and it causes significant delays (average 144 minutes), vomiting (23%), and aspiration risk 6, 7
• Portal venous phase imaging without oral contrast is sufficient 2

Chest Trauma:

• Non-contrast chest CT is adequate for rib fractures and pneumothorax 2
• Add IV contrast only if vascular injury suspected 2

Suspected Physical Abuse in Children:

• CT chest without contrast for rib fractures (more sensitive than radiography) 2
• CT abdomen/pelvis WITH IV contrast for suspected visceral injury 2
• Portal venous phase imaging is most helpful; delayed excretory phase only if genitourinary disruption suspected 2

Hydronephrosis Evaluation

• Initial imaging: Non-contrast CT if cause unknown - best for detecting stones 2, 3
• CT with IV contrast (or CTU) provides more comprehensive evaluation when stone disease excluded and other etiologies suspected 2
• Patients with moderate-severe hydronephrosis and renal colic may benefit from CT to assess stone passage likelihood 2

Pediatric Back Pain

• MRI spine without and with contrast is the modality of choice when infection, inflammation, or tumor suspected 2
• Contrast helpful when clinical or laboratory evidence supports these diagnoses 2
• CT with contrast only if MRI contraindicated or not feasible; performing both without and with contrast usually not indicated 2

Key Contraindications and Precautions

Renal Function Considerations:

• At eGFR <45 mL/min or <30 mL/min (depending on application), hydration and careful review of indication for contrast-enhanced CT is recommended 8
• Gadolinium contrast should be avoided in stage 4-5 chronic kidney disease due to nephrogenic systemic fibrosis risk 5

Allergy History:

• Previous anaphylactic reaction to iodinated contrast is a contraindication 1
• Consider non-contrast CT or alternative imaging (MRI, ultrasound) in patients with true contrast allergies 1

Pregnancy:

• Ultrasound is first-line for most indications 3
• If CT necessary, use lowest possible radiation dose 3
• Limited three-view intravenous urography recommended for urolithiasis if ultrasound negative/equivocal 5

Common Pitfalls to Avoid

• Don't routinely order both non-contrast AND contrast CT - if contrast study planned, non-contrast phase usually doesn't add diagnostic information for most indications 2
• Don't delay trauma CT for oral contrast - it provides no benefit in blunt abdominal trauma and causes significant time delays and aspiration risk 6, 7
• Don't assume contrast always needed for cancer staging - bone metastases and calcifications are better seen without contrast 1
• Don't order contrast-enhanced head CT as first-line for acute mental status changes - non-contrast is appropriate initial test 2
• Don't use contrast for suspected kidney stones - non-contrast CT is the gold standard with 97% sensitivity 3

Age-Specific Modifications

Pediatric Patients:

• Lower threshold for using ultrasound or MRI to minimize radiation exposure 2
• When CT necessary, use lowest possible radiation dose protocols 2
• Contrast decisions follow same principles as adults but with heightened attention to radiation minimization 2

Elderly Patients:

• Higher likelihood of renal impairment - check eGFR before contrast administration 8
• Increased risk of contrast-induced nephropathy - ensure adequate hydration 8
• Consider cumulative radiation exposure from prior studies 3