P-1409. Molecular Detection of Tubercular Lymphadenitis: Real World Evidence for a Novel PCR-Based Assay

TL;DR

This study evaluates a new PCR test, GeneXpert Ultra, for diagnosing tubercular lymphadenitis and finds it has high specificity and improved sensitivity compared to traditional methods.

Contribution

The study provides real-world evidence of GeneXpert Ultra's diagnostic performance in tubercular lymphadenitis, highlighting its value in paucibacillary cases.

Findings

GeneXpert Ultra showed 100% sensitivity and 64.7% specificity against MGIT culture.

Against the composite reference standard, Ultra had 61.1% sensitivity and 100% specificity for probable+definite LNTB.

Ultra demonstrated 83.3% sensitivity and 72.1% specificity for microbiologically confirmed LNTB cases.

Abstract

Tubercular lymphadenitis (LNTB) is the most common form of extrapulmonary tuberculosis (EPTB). GeneXpert Ultra, a cartridge-based nucleic acid amplification test, offers advancements over its predecessor, GeneXpert, including a larger reaction chamber and two additional multi-copy amplification target genes, promising to improve diagnostic accuracy. We conducted a two-year prospective observational study to evaluate the diagnostic accuracy of GeneXpert Ultra in 55 LNTB patients.Table 1.Diagnostic performance of LN GeneXpert Ultra against CRS : definite LNTBTable 2.Diagnostic performance of LN GeneXpert Ultra against CRS: probable+definite LNTB

Diagnostic performance of LN GeneXpert Ultra against CRS : definite LNTB

Diagnostic performance of LN GeneXpert Ultra against CRS: probable+definite LNTB

Participants underwent lymph node biopsy and samples obtained were subjected to Mycobacteria Growth Indicator Tube (MGIT) culture, Ziehl-Neelsen staining, and cytology/histopathology. Diagnostic accuracy of GeneXpert Ultra was assessed against a composite reference standard (CRS) incorporating clinical, histopathological, and microbiological findings. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of Ultra were calculated against both CRS and MGIT culture

Fifty-five participants were included (mean age 33.1 years; 55% female). Ultra was positive in 22 (40%) cases. Against MGIT culture, Ultra showed a sensitivity of 100%, specificity of 64.7%, PPV of 18.2%, and NPV of 100%. However, MGIT culture positivity was low (7.2%), consistent with prior studies reporting low culture yields in lymph node tuberculosis due to paucibacillary samples. Therefore, diagnostic performance was primarily assessed against CRS. Ultra showed a sensitivity of 61.1% (95% CI 43.5–76.9) and specificity of 100% (95% CI 82.3–100), against CRS (confirmed + probable LNTB), with a PPV of 100% and an NPV of 57.6%.When restricted to CRS-confirmed LNTB cases alone, Ultra demonstrated a sensitivity of 83.3% (95% CI 51.6–97.9) and specificity of 72.1% (95% CI 56.3–84.7)

GeneXpert MTB/RIF Ultra demonstrated high specificity and moderate overall sensitivity for diagnosing lymph node tuberculosis, with improved sensitivity among microbiologically confirmed cases. Despite low MGIT culture positivity, Ultra outperformed culture in case detection and represents a valuable diagnostic tool in paucibacillary tubercular lymphadenitis when interpreted alongside clinical and histopathological findings.

All Authors: No reported disclosures

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