Gastrointestinal tuberculosis: Diagnostic approaches for this uncommon pathology

Table 1 Summary of diagnostic tools useful in abdominal tuberculosis

Diagnostic tools
Clinical signs	Vary according to site of infection (luminal, visceral, peritoneal)
	Non-specific and may only be present in late stage of disease
Imaging	Ultrasound is useful as a non-invasive imaging modality and can guide fine needle aspiration to obtain tissue for diagnosis of visceral TB, but has low sensitivity and specificity
	Cross-sectional abdominal imaging is non-specific but recommended to assess extent of TB infection and identify complications
Endoscopy	Gross endoscopic appearance may mimic other diseases such as Crohn’s (Figure 1)
	Facilitates targeted tissue biopsy for histological and microbiological examination
Histopathology	Characteristic tissue features include granulomas with caseating necrosis, Langerhans giant cells, chronic ulcers lined by conglomerate epithelioid histiocytes and disproportionate submucosal inflammation
Conventional microbiology	Ziehl Nelsen staining of acid-fast bacilli provides rapid diagnosis with high specificity
	Both staining and culture have low sensitivity
	Due to slow growth rate of M. tuberculosis, culture may require 6-8 weeks
Molecular	PCR provides very high specificity across all specimen types
	PCR sensitivity is superior in tissue compared to ascitic fluid or paraffin-embedded specimens
	Stool PCR and cell-free DNA have potential as alternative, non-invasive tests but require further evaluation to confirm diagnostic performance
Serology	T-cell based IGRA, including QuantiFERON® and T-SPOT® on blood or ascitic fluid cannot differentiate between latent and active infection but can complement other diagnostic modalities
	Poor sensitivity in patients who are immunocompromised or who have disseminated disease

TB: Tuberculosis; IGRA: Interferon-gamma release assays; M. tuberculosis: Mycobacterium tuberculosis.