How do you diagnose a blockage in the body?

Diagnosing Blockages in the Body

The diagnostic approach depends critically on the type and location of suspected blockage—the term "blockage" encompasses diverse pathologies requiring different testing strategies.

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Gastrointestinal Tract Blockages

Large Bowel Obstruction

CT abdomen and pelvis with IV contrast is the primary imaging study for suspected large bowel obstruction, with sensitivity of 93-96% and specificity of 93-100% for confirming obstruction, identifying the cause, and determining the site 1.

• Alternative imaging options 1:

  • Water-soluble contrast enema: sensitivity 96%, specificity 98% when CT unavailable
  • Abdominal ultrasound: moderate sensitivity (88%) as screening test
  • Plain abdominal X-rays: limited utility (sensitivity 74-84%, specificity 50-72%), use only when other modalities unavailable

• Special considerations: If perforation is suspected, CT is recommended for stable patients to define cause and site, but should not delay surgical treatment in cases of diffuse peritonitis 1

Biliary Obstruction (Gallstones/Bile Duct Blockage)

Trans-abdominal ultrasound combined with liver biochemical tests (ALT, AST, bilirubin, ALP, GGT) should be performed as first-line investigations 2.

• Risk stratification for common bile duct stones 2:

  • Very strong predictor: Direct visualization of CBD stone on ultrasound
  • Strong predictors: CBD dilation on ultrasound, bilirubin >4 mg/dL
  • Moderate predictors: Abnormal liver function tests, age >55 years, clinical gallstone pancreatitis

• Diagnostic performance: Normal liver biochemical tests have 97% negative predictive value for CBD stones, but only 15% positive predictive value 2

• Further imaging for moderate-risk patients: Consider MRCP, endoscopic ultrasound, intraoperative cholangiography, or laparoscopic ultrasound 2

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Cardiac Conduction Blockages (Heart Block)

Initial Evaluation

All patients require documented history, physical examination, ECG, and echocardiogram 3.

• First-degree AV block: ECG shows PR interval prolongation 3

  • If PR <0.3 seconds with normal QRS: no further testing needed unless structural heart disease suspected
  • If PR ≥0.3 seconds or abnormal QRS: obtain exercise stress test, 24-hour ambulatory monitor, and echocardiogram 3

• Second-degree AV block (Wenckebach/Type I): May be normal in endurance athletes 3

  • Assess for symptoms and structural heart disease with echocardiogram
  • If abnormal QRS or shortest PR ≥0.3 seconds: 24-hour ECG monitoring warranted 3

• Second-degree AV block (Mobitz/Type II): Always abnormal 3

  • Requires history, physical examination, and echocardiogram regardless of symptoms
  • Stress test or electrophysiologic study (EPS) may be needed to distinguish from 2:1 Wenckebach 3

Exercise-Induced Block

Exercise testing is indicated when syncope occurs during or shortly after exertion 3.

• Diagnostic criteria: Mobitz II second-degree or third-degree AV block developing during exercise is diagnostic even without syncope 3
• Monitoring: Careful ECG and blood pressure monitoring during both test and recovery phases 3

Advanced Testing

Electrophysiologic study (EPS) should be performed when 3:

• Wenckebach AV block coexists with bundle-branch block
• Any indication of risk for progression to higher-degree block
• Exercise-induced type I second-degree AV block appears (to evaluate for intra-His or infra-His block)

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Vascular Blockages

Deep Vein Thrombosis

Compression ultrasonography is the diagnostic standard, as history and physical examination alone have poor discriminative value (ROC area 0.68) 4.

• Clinical assessment limitations: Even in low-risk groups based on clinical scoring, DVT probability remains 15% 4
• Key predictors (though insufficient alone): male gender, duration of symptoms, malignancy, immobilization, leg trauma, pain when walking, edema, calf circumference difference, dilated veins 4

Coronary Artery Blockage

Cardiac catheterization with coronary angiography should be performed when myocardial ischemia or infarction is suspected 3.

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Urinary Tract Blockages

Clinical Recognition

Urinary obstruction presents with inability to completely empty the bladder, with mice/patients not urinating during handling or abdominal palpation 3.

• Physical findings: Bulge or swelling in caudal abdomen, enlarged bladder on palpation, in males may see distended/abnormally colored penis (dark red to purple) 3
• Complications: Often leads to hydronephrosis (kidney swelling) palpable in dorsal abdomen 3

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General Principles Across All Blockage Types

History and Physical Examination

A documented history and physical examination must be performed for all patients, though these alone have limited diagnostic value and require objective testing 3, 4, 5.

• History should include: chronology and symptomatology of presenting complaints, onset, quality, intensity, distribution, and duration 3
• Physical examination: focused on the suspected organ system with attention to specific findings (e.g., abdominal palpation for masses, cardiac auscultation for murmurs) 3, 5

Imaging Selection

The choice of imaging modality should be guided by the suspected location and type of blockage, with CT generally offering superior sensitivity and specificity for most anatomical blockages 1.

Common Pitfall

Avoid relying solely on clinical assessment or basic screening tests when objective blockage is suspected—the predictive value of history and physical examination is consistently low across multiple organ systems, necessitating definitive imaging or specialized testing 4, 5.