What is the complete workup for Gastrointestinal (GI) Tuberculosis (TB), including daily orders?

Complete Workup for Gastrointestinal Tuberculosis

Initial Diagnostic Evaluation

The workup for GI TB requires obtaining tissue for histology and microbiology through endoscopy or imaging-guided biopsy, combined with radiologic assessment and microbiological confirmation using acid-fast bacilli smears, culture, and molecular testing. 1, 2, 3

Clinical Assessment

• Document abdominal pain characteristics, weight loss, fever, anorexia, change in bowel habits, nausea, and vomiting 2
• Assess for risk factors: immigration from endemic areas, HIV status, immunosuppression, homelessness, incarceration, or long-term care facility residence 2
• Examine for evidence of pulmonary TB (present in <50% of GI TB cases) 2

Laboratory Studies

• Complete blood count with differential 3
• Liver function tests (baseline AST, ALT, bilirubin, alkaline phosphatase) - essential before initiating treatment 4
• HIV testing within 2 months of diagnosis 5
• Tuberculin skin test (TST) or interferon-gamma release assay (IGRA) 6
• Ascitic fluid analysis if ascites present: cell count, protein, adenosine deaminase (ADA) - elevated ADA provides diagnostic specificity 3

Imaging Studies

• Chest radiograph to evaluate for pulmonary TB 6
• Abdominal CT or MRI to identify peritoneal involvement, lymphadenopathy, bowel wall thickening, strictures, or masses 3
• Ultrasound as initial imaging modality in resource-limited settings 3
• PET scan occasionally helpful for diagnostic uncertainty 3

Endoscopic Evaluation

• Upper endoscopy for gastroduodenal involvement: look for ulcers, strictures, masses, or fistulas 1
• Colonoscopy for ileocecal disease (most common site): obtain multiple biopsies from ulcer edges and elevated lesions 1, 3
• Deep biopsies or endoscopic mucosal resection for adequate tissue sampling 1
• Obtain at least 6-8 biopsy specimens from affected areas for both histology and culture 3

Microbiological Confirmation

• Acid-fast bacilli (AFB) smear from tissue specimens 6, 2
• Mycobacterial culture with species identification - gold standard but takes 6-8 weeks 6, 2
• Xpert MTB/RIF or similar PCR-based testing on tissue specimens (low sensitivity but rapid results) 1, 3
• Drug susceptibility testing on all initial isolates for isoniazid, rifampin, pyrazinamide, and ethambutol 6, 5

Histopathological Examination

• Look for granulomas with or without caseating necrosis 1, 3
• Identify ulcers lined by histiocytes 3
• Presence of AFB on histology 1

Treatment Initiation

Begin standard four-drug anti-TB therapy immediately once diagnosis is established or highly suspected, using isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months, followed by isoniazid and rifampin for 4 months (total 6 months). 5, 7, 1

Standard Regimen Dosing (Initial 2-Month Phase)

• Isoniazid: 5 mg/kg daily (max 300 mg) 5
• Rifampin: 10 mg/kg daily (max 600 mg) 5
• Pyrazinamide: 35 mg/kg daily for patients <50 kg; 2.0 g daily for patients ≥50 kg 5
• Ethambutol: 15 mg/kg daily 5

Continuation Phase (Months 3-6)

• Isoniazid and rifampin daily or 2-3 times weekly under directly observed therapy 5
• Discontinue ethambutol once susceptibility to isoniazid and rifampin confirmed 5

Modified Regimens for Special Circumstances

For isolated hyperbilirubinemia: Avoid pyrazinamide; use rifampin, ethambutol, and fluoroquinolone with weekly liver function monitoring 4

For drug-resistant TB: Use BPaLM regimen (bedaquiline, pretomanid, linezolid, moxifloxacin) for 6 months if MDR/RR-TB confirmed 8

Daily Orders During Hospitalization

Day 1-2

• NPO if obstruction suspected, otherwise regular diet as tolerated
• IV fluids: Normal saline at maintenance rate if NPO
• Anti-TB medications (as dosed above) - give daily in morning 5
• Pyridoxine (Vitamin B6) 25-50 mg daily to prevent isoniazid-induced neuropathy 5
• Monitor vital signs every 4 hours
• Daily weight
• Strict intake/output monitoring
• Airborne isolation precautions until pulmonary TB excluded 6

Ongoing Daily Orders

• Continue anti-TB medications daily
• Liver function tests: Weekly for first 2 weeks, then at weeks 4,6, and 8 4
• Discontinue ATT immediately if AST/ALT >5× upper limit of normal or bilirubin above normal 4
• Monthly sputum cultures if pulmonary involvement present 8
• Nutritional supplementation as needed for weight loss
• Physical therapy consultation for debilitated patients
• Social work consultation for directly observed therapy (DOT) arrangement 5

Monitoring for Complications

• Gastric outlet obstruction: Consider endoscopic balloon dilation if tight stricture develops 1
• Perforation or massive bleeding: Surgical consultation 3
• Hepatotoxicity: Hold all hepatotoxic drugs, reintroduce sequentially after normalization 4

Response Assessment

• Endoscopic re-evaluation at 2 months to assess mucosal healing - objective endpoint for response 3
• Resolution of ascites by 2 months if present initially 3
• Fecal calprotectin may be used as biomarker for intestinal TB response 3

Critical Pitfalls to Avoid

• Do not delay treatment waiting for culture results if clinical suspicion is high - cultures take 6-8 weeks and GI TB diagnosis is often delayed 6, 2
• Do not use rifampin-pyrazinamide combination for latent TB due to severe hepatotoxicity risk 6
• Do not continue pyrazinamide in patients with hyperbilirubinemia - it is the most hepatotoxic first-line agent 4
• Do not assume negative chest X-ray excludes TB - pulmonary disease absent in >50% of GI TB cases 2
• Do not confuse with Crohn's disease - GI TB closely mimics inflammatory bowel disease; obtain adequate tissue for diagnosis 3
• Do not use intermittent dosing without DOT - nonadherence results in larger proportion of missed doses 6, 5

HIV Co-infection Considerations

• Extend treatment to 9 months for HIV-positive patients with CD4+ <100 cells/mm³ 8, 5
• Use daily therapy during intensive phase, then daily or three times weekly during continuation 5
• Coordinate antiretroviral therapy timing with infectious disease specialist 5