Investigations for Abdominal Tuberculosis

1. Routine Blood Tests

• CBC: Mild normocytic anaemia, normal or mildly elevated WBC; lymphocytosis may be present
• ESR / CRP: Elevated (non-specific, supports active infection)
• Serum albumin: Often low (chronic disease, malnutrition)
• LFTs: Assess hepatic involvement in disseminated disease

2. Tuberculin Skin Test (TST) / IGRA

• Mantoux (TST) or Interferon-Gamma Release Assay (IGRA) — detect M. tuberculosis infection, not active disease
• A positive result does not confirm active intestinal TB; a negative result does not exclude it (especially in HIV-positive patients, elderly, or malnourished)
• These are adjunctive, not diagnostic on their own

"A positive tuberculin skin test or IGRA is not very helpful because a positive test does not necessarily mean active disease. Many patients, especially older persons and those with HIV infection, have a negative skin test in the face of active intestinal TB." — Sleisenger and Fordtran's Gastrointestinal and Liver Disease

3. Stool Examination

• Stool for AFB (Ziehl-Neelsen stain): Low sensitivity
• Stool PCR for M. tuberculosis: More sensitive (~65%) — useful when endoscopy is not feasible

4. Imaging

Chest X-Ray

• Mandatory in all cases; active/prior pulmonary TB supports the diagnosis
• Note: chest X-ray is normal in most cases of isolated intestinal TB

Contrast-Enhanced CT Abdomen (most useful single imaging modality)

• Ileocecal thickening with involvement on both sides of the ileocecal valve (valve incompetence)
• Asymmetric bowel wall thickening
• Massive mesenteric/retroperitoneal lymphadenopathy with central low attenuation (caseous necrosis) — highly characteristic
• Peritoneal thickening and ascites (in TB peritonitis)
• Calcified mesenteric lymph nodes (chronic/healed disease)
• Contracted cecum (conification)

Barium Studies (now largely replaced by CT/endoscopy)

• Barium enema / Small bowel follow-through: Shows mucosal fold distortion, ulceration, strictures, bowel stenosis, pseudopolyps
• Stierlin sign: Conification/rapid emptying of the cecum — characteristic of TB on barium enema
• Distorted, incompetent ileocecal valve

Ultrasound Abdomen

• Can demonstrate ascites, lymphadenopathy, bowel wall thickening
• Useful as initial/bedside tool; less specific than CT

5. Colonoscopy with Biopsy (Most Useful Single Procedure)

"Colonoscopy with biopsy specimens for histopathology, acid-fast bacilli staining/PCR, and culture (with drug sensitivities) is the most useful procedure for diagnosis." — Sleisenger and Fordtran's Gastrointestinal and Liver Disease

• Histopathology (H&E stain): Caseating granulomas seen in 50–80% of cases
• Ziehl-Neelsen (AFB) stain: Positive in ~20% of mucosal samples — low sensitivity
• PCR for M. tuberculosis: More sensitive (~65%); can detect even when AFB stain is negative
• Mycobacterial culture with drug sensitivity testing: Gold standard but takes 4–8 weeks

6. Ascitic Fluid Analysis (for TB Peritonitis)

"The diagnosis of tuberculous ascites may be established definitively by demonstration of M. tuberculosis in ascitic fluid... Adenosine deaminase may be measured in ascitic fluid, with high levels observed in patients with tuberculosis." — Sleisenger and Fordtran's Gastrointestinal and Liver Disease

7. Laparoscopy + Peritoneal Biopsy

• Indicated when diagnosis cannot be confirmed by less-invasive methods
• Visualises peritoneal tubercles, omental thickening, adhesions
• Biopsy of peritoneum/omentum: Sent for histology (caseating granulomas), AFB stain, PCR, and culture
• Highest diagnostic yield for TB peritonitis

"If the diagnosis of tuberculous peritonitis is strongly suspected and cannot be confirmed with the methods described above, abdominal laparoscopy with histologic analysis of the peritoneum should be considered." — Sleisenger and Fordtran's Gastrointestinal and Liver Disease

8. Sputum AFB Smear & Culture

• Relevant when active pulmonary TB is suspected concurrently
• A positive sputum result supports but does not confirm abdominal TB

9. HIV Testing

• Mandatory in all cases — HIV markedly increases TB risk and alters management

Summary Table