Study of Diagnostic Yield of Nucleic Acid Amplification Test among Tuberculous Cervical Lymphadenitis in Immunocompetent Patients.

BACKGROUND

The most common form of extrapulmonary tuberculosis (TB) is tuberculous lymphadenitis, which constitutes about 30-40% of all extrapulmonary TB cases. A new diagnostic method like the nucleic acid amplification test (NAAT) is a very sensitive and rapid test for diagnosing tuberculous cervical lymphadenopathy. It also detects rifampicin sensitivity among positive patients.

OBJECTIVES

(1) To evaluate the diagnostic yield of TrueNAT for detecting Mycobacterium tuberculosis bacteria in the fine-needle aspirated samples of cervical lymph nodes compared with Ziehl-Neelsen (ZN) staining; (2) to evaluate the diagnostic yield of TrueNAT for diagnosis of tuberculosis through comparison with the cytology report of fine-needle aspiration (FNA) sample of cervical lymph node and with necrotic cervical lymph node on ultrasonography (USG) neck.

MATERIALS AND

METHODS

A total of 50 patients enrolled in this prospective study from January to December 2022. Demographic profile and clinical history were noted. Fine-needle aspirate samples were sent for TrueNAT assay, cytological examination, and ZN staining. USG neck was done for necrotic findings in the cervical lymph nodes.

RESULTS

The TrueNAT positivity rate was 70%. TrueNAT sensitivity and specificity were assessed according to the cytology report, acid-fast bacilli (AFB) positivity on ZN stain, and the finding of necrosis in the cervical lymph node on the USG neck. The sensitivity and specificity of the TrueNAT assay were 80.49 and 77.78%, respectively, in accordance with necrosis on FNA cytology; 17.14 and 93.33%, respectively, in accordance with AFB positivity on ZN stain; and 74.29 and 33.33%, respectively, in accordance with lymph node necrosis on USG neck.

CONCLUSION

The TrueNAT assay should be used as an adjunctive test in addition to the conventional cytological examination of the FNA sample of lymph nodes for the rapid diagnosis of tuberculosis. It also detects rifampicin resistance simultaneously.