Comparison of the modified fluorescent method and conventional Ziehl-Neelsen method in the detection of acidfast bacilli in lymphnode aspirates

Abstract

Objectives: The objectives were to correlate the modified fluorescent method with the conventional Ziehl-Neelsen (ZN) method for the detection of acid-fast bacilli (AFB) and, also to study the efficacy and advantages of using the auramine-rhodamine stain on lymph node aspirates under fluorescent microscopy.

Methods: In 108 consecutive patients with a clinical suspicion of tuberculosis (TB) presenting with lymphadenopathy, fine needle aspirations were performed. Smears from the aspirates were processed for routine cytology, the conventional ZN method, and the modified fluorescent method. The significance of the modified fluorescent method over the conventional ZN method was analyzed using the chi-square test.

Results: Out of 108 aspirates, 102 were studied and remaining 6 were excluded from the study due to diagnosis of malignancy in 4.04% (4/6) and inadequate aspiration in 2.02% (2/6). Among the 102 aspirates, 44.11% (45/102) were positive for AFB on the conventional ZN method, 58.9% (60/102) were indicative of TB on cytology, while the smear positive increased to 81.37% (83/102) on the modified fluorescent method.

Conclusions: Fluorescent microscopy has the advantage of speed and ease of screening, and reduces observer fatigue. The modified fluorescent method was found to be more advantageous than routine cytology and conventional ZN method, particularly in paucibacillary cases. The bacillary positivity rates were higher in the modified fluorescent method than in the ZN method. Hence, the modified fluorescent method can be an adjuvant when used with routine cytology for the identification of AFB.

Keywords: Cytology; Ziehl–Neelsen stain; fluorescent method; tuberculosis.

Figure 1

Smear showing acid fast bacilli typically fluorescing as golden, slender, rod-shaped bacilli (single arrow head). Also seen are some naturally fluorescent particles (double arrow head) adjacent to bacilli (AR, ×1000)

Figure 2

Smear showing viable acid fast bacilli appearing with more intense fluorescence (double arrow head) when compared with some acid fast bacilli (single arrow head) appearing less fluorescence (AR, ×1000)