When should an abdominal computed tomography (CT) scan be ordered with or without contrast in patients with acute abdominal pain, suspected appendicitis, abdominal trauma, or other abdominal pathologies, considering factors such as history of contrast allergy, impaired renal function, pregnancy, or pediatric status?

When to Order Abdominal CT Scan With or Without Contrast

For most adults with acute abdominal pain, order CT abdomen/pelvis with IV contrast only—this provides optimal diagnostic accuracy (sensitivity 96-100%, specificity 93-95%) while avoiding unnecessary delays and radiation from oral contrast. 1, 2

Standard Protocol for Adults with Acute Abdominal Pain

Order CT with IV contrast alone for the following clinical scenarios:

• Nonlocalized abdominal pain with fever (suspected abscess, diverticulitis, cholangitis) 1
• Suspected appendicitis in non-pregnant adults 2, 3
• Acute abdominal pain requiring broad differential diagnosis 1
• Suspected complicated intra-abdominal infections 1, 3

The ACR Appropriateness Criteria explicitly state that precontrast images are not required for diagnosis in nonlocalized abdominal pain, and a single postcontrast phase is sufficient. 1 IV contrast increases sensitivity to 96% compared to 91% for unenhanced CT, and significantly expands the spectrum of detectable pathology. 1, 4

Why Skip Oral Contrast

Do not routinely use oral contrast—it requires 40 minutes to 2+ hours for bowel transit, is poorly tolerated by patients with nausea/vomiting, and provides no diagnostic advantage over IV contrast alone. 2 Multiple studies demonstrate that oral contrast does not improve diagnostic accuracy for appendicitis or other acute abdominal pathology. 2, 5 The ACR guidelines note that many institutions have abandoned routine oral contrast due to delays in scan acquisition without meaningful diagnostic benefit. 1

When to Order CT Without Contrast

Order unenhanced CT only when IV contrast is contraindicated:

• Severe contrast allergy (anaphylaxis history) 2
• Severe renal failure (eGFR <30 mL/min/1.73m²) 2
• Suspected urolithiasis (stones are better visualized without contrast)

Unenhanced CT still maintains reasonable diagnostic accuracy with sensitivity 90-96% and specificity 96-100% for appendicitis, though it has limitations in characterizing complicated appendicitis (perforation, abscess). 2, 4 For suspected renal stones, unenhanced CT is actually preferred as contrast obscures calcifications.

When to Order CT With Both IV and Oral Contrast

Rarely indicated in acute settings. The combination approximately doubles radiation exposure without improving diagnostic performance compared to IV contrast alone. 2 Consider only for:

• Suspected small bowel obstruction where oral contrast may help delineate transition points (though this is debated)
• Chronic abdominal pain workup (non-emergent)

Special Populations Requiring Different Approaches

Children and Adolescents

Start with ultrasound first (sensitivity 76%, specificity 95%) to avoid radiation exposure. 2, 3, 6 Only proceed to CT with IV contrast if ultrasound is equivocal/non-diagnostic and clinical suspicion persists. 2, 6 Point-of-care ultrasound by experienced emergency physicians achieves even higher accuracy (sensitivity 91%, specificity 97%). 3

Pregnant Patients

Start with ultrasound first. 2, 3 If ultrasound is inconclusive, proceed to MRI without IV contrast (sensitivity 94%, specificity 96%) rather than CT to avoid fetal radiation exposure. 2, 3 CT should be reserved only when MRI is unavailable and clinical urgency demands immediate diagnosis.

Elderly Patients

CT with IV contrast is strongly recommended due to higher rates of atypical presentations, complicated appendicitis, and mortality in this population. 3 Do not rely on clinical examination alone, as peritoneal signs may be blunted.

Clinical Decision Algorithm

High clinical suspicion (fever >38°C, guarding/rigidity, WBC >10,000 with left shift):

• Adults: CT abdomen/pelvis with IV contrast immediately 2, 3
• Children: Ultrasound first, then CT with IV contrast if equivocal 6
• Pregnant: Ultrasound first, then MRI if equivocal 2, 3

Intermediate clinical suspicion (some abdominal pain, mild tenderness, equivocal labs):

• Adults: CT abdomen/pelvis with IV contrast 2, 3
• Children: Ultrasound first 6
• Pregnant: Ultrasound first 2

Low clinical suspicion (minimal findings, normal labs):

• Consider observation without imaging 3
• If imaging needed, ultrasound in children/pregnant patients 6

Common Pitfalls to Avoid

Do not order CT with oral contrast for suspected appendicitis—this delays diagnosis by 1-3 hours without improving accuracy and is poorly tolerated by patients with nausea. 2

Do not skip IV contrast in adults unless contraindicated—unenhanced CT has lower sensitivity (91% vs 96%) and misses important findings like periappendiceal inflammation, abscess formation, and alternative diagnoses. 1, 4

Do not proceed directly to CT in children—ultrasound first significantly reduces radiation exposure while maintaining acceptable diagnostic accuracy. 6 Studies show ultrasound-first strategies decrease CT utilization without compromising outcomes.

Do not dismiss appendicitis based on negative imaging alone if clinical suspicion remains high—consider observation, repeat examination, or surgical consultation. 2, 3 Imaging has false-negative rates of 4-9%.

Do not order "CT with and without contrast" (pre- and post-contrast phases) for acute abdominal pain—this doubles radiation exposure and is unnecessary for diagnosis. 1 This protocol is reserved for specific oncologic indications, not acute abdominal pathology.

Impact on Clinical Outcomes

CT with IV contrast changes the leading diagnosis in 49% of emergency department patients with abdominal pain, alters admission decisions in 24%, and modifies surgical plans in 25%. 1 The use of CT has reduced negative appendectomy rates from historical 14.7% to current 1.7-7.7%. 3 These data strongly support liberal use of CT with IV contrast in adults with acute abdominal pain when clinical evaluation is inconclusive.