From the Research
Diagnostic markers for non-pulmonary tuberculosis include microbiological, immunological, and radiological findings specific to extrapulmonary sites, with microbiological confirmation through culture or nucleic acid amplification tests (NAATs) like GeneXpert MTB/RIF from affected tissue samples providing definitive diagnosis. The most recent and highest quality study 1 highlights the utility of the GeneXpert MTB/RIF assay on paraffin-embedded biopsy tissue samples for detecting tuberculosis, with a detection rate of 26.3% in histopathologically diagnosed cases of TB.
Key diagnostic markers for non-pulmonary TB include:
- Microbiological confirmation through culture or NAATs like GeneXpert MTB/RIF from affected tissue samples
- Histopathological examination showing caseating granulomas, which is highly suggestive of TB
- Immunological tests, such as tuberculin skin tests (TST) and interferon-gamma release assays (IGRAs) like QuantiFERON-TB Gold, which indicate TB infection but cannot distinguish between active and latent disease
- Site-specific markers, including elevated adenosine deaminase (ADA) levels in pleural, peritoneal, or cerebrospinal fluid (>40 U/L in TB meningitis), and elevated CA-125 in peritoneal TB
- Radiological findings, which vary by site, such as spine TB (Pott's disease) showing vertebral destruction and paraspinal abscesses, lymph node TB presenting as matted nodes with central necrosis, and genitourinary TB showing calcifications and strictures
- Molecular markers, like lipoarabinomannan (LAM) in urine, which are useful in HIV-positive patients
These markers must be interpreted in clinical context, as non-pulmonary TB often presents with non-specific symptoms and can mimic other conditions, making diagnosis challenging without a combination of these diagnostic approaches 2, 3, 4. The GeneXpert MTB/RIF assay has been shown to be a rapid and accurate tool for detecting MTB in smear-negative sputum specimens 3 and has the capacity to improve the diagnosis of tuberculous meningitis cases 2.