Will a Kidney, Ureter, Bladder (KUB) imaging study detect a foreign body in the stomach or intestines?

KUB Imaging for Foreign Bodies in Stomach and Intestines

KUB (plain abdominal radiography) has significant limitations for detecting foreign bodies in the stomach and intestines, with false-negative rates reaching 47% for esophageal foreign bodies and up to 85% for non-radiopaque objects like food, fish bones, chicken bones, wood, and plastic—therefore, a negative KUB does not rule out foreign body ingestion, and CT scan should be performed in symptomatic patients or those with high clinical suspicion. 1, 2

What KUB Can Detect

• Radiopaque foreign bodies appear as oval or round opaque objects, sometimes surrounded by a gas halo, with reported sensitivity ranging from 74% to 100% for visible objects 3, 4
• Pneumoperitoneum indicating perforation can be identified on upright or lateral decubitus views 5
• General location and orientation of radiopaque objects when present 5

Critical Limitations of KUB

• False-negative rate of 47% for esophageal foreign bodies overall 1, 2
• False-negative rate up to 85% for food bolus, fish bones, chicken bones, and all non-radiopaque materials 1, 2
• Radiolucent objects are invisible, including most organic materials (wood, plastic, food), making plain films unreliable for excluding foreign bodies 1, 4
• Overlying bowel gas and fecal material can obscure visualization of foreign bodies 4

When to Proceed Directly to CT Scan

CT scan (without IV contrast) should be performed without delay in the following situations:

• Any symptomatic patient regardless of KUB findings 1, 2
• Suspected perforation (fever, peritoneal signs, persistent pain) 5, 2
• Persistent symptoms >24-48 hours despite negative plain films 1, 2
• High clinical suspicion for non-radiopaque object ingestion 1, 2
• Suspected complications including bowel obstruction, abscess, or free air 5, 1

CT Performance Characteristics

• Sensitivity of 90-100% for detecting foreign bodies 1, 2, 6
• Specificity of 93.7-100% for foreign body detection 1, 2
• Superior for non-radiopaque objects that are invisible on plain films 1, 2, 6
• Essential for evaluating complications including perforation, abscess formation, and bowel obstruction 5, 1, 2

Imaging Protocol Recommendations

For initial evaluation:

• Obtain anteroposterior and lateral views of chest, abdomen, and pelvis on plain films 5, 2
• Use contrast-enhanced CT only if perforation is suspected in hemodynamically stable patients 5, 2
• Use unenhanced CT for foreign body detection, as contrast can obscure visualization of ingested packets 3

Common Pitfalls to Avoid

• Do not rely on negative KUB to exclude foreign body ingestion in symptomatic patients 1, 2
• Do not delay CT imaging in patients with persistent symptoms or high clinical suspicion 1, 2
• Do not use contrast-enhanced CT as the primary modality for foreign body detection, as it may obscure visualization 3
• Do not delay surgical intervention for imaging in hemodynamically unstable patients 5, 2

Laboratory Workup When Indicated

Obtain the following if perforation is suspected or intervention is planned:

• Complete blood count (CBC) 1, 2
• C-reactive protein (CRP) and procalcitonin 5, 1
• Serum creatinine 5, 2
• Lactate and blood gas analysis 1, 2