Comparison of CBNAAT and AFB screening using Ziehl Neelsen stain and fluorescent stain on FNAC sample for rapid diagnosis of tubercular lymphadenitis

Abstract

: Tuberculous lymphadenitis is the most common etiology of cervical lymphadenopathy in endemic countries. Fine needle aspiration of palpable lymph nodes is done for rapid diagnosis of tuberculous lymphadenitis This study presents a comparative evaluation of fine needle aspiration cytology (FNAC) with acid fast bacilli screening using Ziehl Neelsen stain, Fluorescent stain with Cartridge based nucleic acid amplification test (CBNAAT) for the rapid diagnosis of tubercular lymphadenitis.: An observational cross sectional study was done over a period of 15 months from January 2020 to March 2021. All newly diagnosed cases of tubercular lymphadenitis irrespective of age and sex were included. Fine needle aspiration was performed from the palpable lymph node. Smears were prepared using Giemsa, Papanicolaou, Ziehl Neelsen and Auramine O stain.Rest of the sample was used for Mycobacterial growth indicator test (MGIT) and CBNAAT. Statistical Analysis was performed using McNemar test. For gold standard, MGIT as well as a composite reference standard on parameters that included MGIT, radiological findings of tuberculosis, Positive Mantoux test and Positive response to ATT seen in the form of complete resolution of clinical and radiological findings.: The diagnostic value of CBNAAT differed with respect to the chosen gold standard. With MGIT as gold standard, CBNAAT had the highest sensitivity, specificity, positive predictive value and negative predictive value. The diagnostic accuracy of CBNAAT was also the highest. Using CRS (Composite Reference standard) as gold standard, CBNAAT showed the highest specificity and positive predictive value.: With CBNAAT showing statistically significant data of a higher diagnostic value in our study as well as showing rapid result, being automated and not subjected to observer interpretation, we conclude that CBNAAT is more efficient in the diagnosis of tubercular lymphadenitis as compared to AFB screening methods. The only limitation of CBNAAT in our study was its ability to show positive results for three atypical mycobacteria due to possible cross contamination.