What is the initial imaging study for a patient with new‑onset right upper quadrant (RUQ) pain?

Initial Imaging for Right Upper Quadrant Pain

Ultrasound of the abdomen is unequivocally the first-line imaging study for any adult patient presenting with new-onset right upper quadrant pain. 1, 2

Why Ultrasound First

The American College of Radiology assigns ultrasound the highest appropriateness rating of 9/9 ("usually appropriate") for RUQ pain evaluation, making it the clear initial choice over all other modalities. 1, 2 This recommendation holds regardless of whether you suspect biliary disease, hepatic pathology, or other causes. 1

Key advantages that make ultrasound superior as the initial test:

• 96% accuracy for detecting gallstones, the most common cause of RUQ pain 1
• No ionizing radiation exposure, critical for younger patients and those requiring repeat imaging 2
• Rapid study completion with immediate morphologic evaluation of the gallbladder, bile ducts, liver, and adjacent structures 1
• Identifies alternative diagnoses beyond biliary disease in more than one-third of cases 3
• Cost-effective and widely available in emergency settings 2, 4

When Ultrasound Performance Is Limited

Ultrasound has important limitations you must recognize:

• Critically ill patients commonly show gallbladder abnormalities (wall thickening, sludge) without true acute cholecystitis, reducing specificity 1, 2
• Sensitivity for acute cholecystitis is only 88% (compared to 97% for cholescintigraphy), meaning negative ultrasound does not exclude disease if clinical suspicion remains high 1
• The sonographic Murphy sign has relatively low specificity and is unreliable if the patient received pain medication before imaging 1

Escalation Algorithm When Ultrasound Is Nondiagnostic

If ultrasound findings are equivocal or negative but clinical suspicion remains high, proceed systematically:

For suspected acute cholecystitis specifically:

• Cholescintigraphy (HIDA scan) demonstrates 96% sensitivity and 90% specificity, outperforming ultrasound 2, 3
• Order HIDA when ultrasound shows only one finding (e.g., sludge alone) but clinical features suggest cholecystitis 2

For suspected complications or alternative diagnoses:

• CT abdomen/pelvis with IV contrast is rated 6-7/9 ("may be appropriate" to "usually appropriate") for second-line imaging 2
• CT is essential when you suspect perforation, abscess, gangrenous cholecystitis, or need to evaluate non-biliary causes 2
• CT detects acute non-gallbladder abnormalities missed by ultrasound in 32% of cases, including pancreatitis, appendicitis, colitis, and vascular emergencies 5

For pregnant patients with equivocal ultrasound:

• MRI without contrast is the preferred next step to avoid radiation 2

Critical Pitfalls to Avoid

Never skip ultrasound and proceed directly to CT unless the patient is hemodynamically unstable—CT has only 75% sensitivity for gallstones and exposes patients to unnecessary radiation. 2

Never order non-contrast CT for suspected cholecystitis—you cannot detect critical findings like gallbladder wall enhancement, pericholecystic hyperemia, or vascular complications without IV contrast. 2

Do not assume normal ultrasound excludes all pathology—if clinical suspicion is high (fever, leukocytosis, persistent pain, positive Murphy sign), proceed to HIDA scan or contrast-enhanced CT rather than discharging the patient. 1, 2

Do not rely on ultrasound alone in critically ill ICU patients—these patients frequently have acalculous cholecystitis or gallbladder abnormalities from other causes, requiring correlation with clinical findings and often additional imaging. 1, 2

Evidence Strength

This ultrasound-first approach is supported by the 2019 ACR Appropriateness Criteria 1 and reinforced by 2026 consensus guidelines 2, representing the highest level of imaging guideline evidence. While one 2020 retrospective study suggested CT is "noninferior" to ultrasound for cholecystitis diagnosis 5, this contradicts established guidelines and ignores radiation exposure, cost, and the ability of ultrasound to guide immediate bedside clinical decisions. The guideline consensus remains that ultrasound-first with selective escalation balances diagnostic accuracy with patient safety. 2