AFB staining in cytodiagnosis of tuberculosis without classical features: a comparison of Ziehl-Neelsen and fluorescent methods

Fine needle aspirates (FNA) were obtained from lymph node and other sites in 250 suspected cases of tuberculosis. Twenty-four cases proved to be non-tubercular on FNA smears and served as negative controls. Of the smears obtained from the remaining 226 cases, 233 were classified into five groups based on cytomorphological features, i.e. presence of necrosis and granulomas, necrosis alone or acute inflammatory exudate (AIE) with or without granuloma. Cases with AIE alone formed the largest group (n = 123). Staining for AFB was done by Ziehl-Neelsen (ZN) and fluorescent methods in all 250 cases. A correlation of AFB positivity and its semiquantitative scoring (1+ to 3+) with the cytomorphological spectrum was done. Overall AFB positivity by ZN staining was 33.5% and by fluorescent staining 45.4%. When the two methods were combined, AFB positivity was 58.7%. Fluorescent staining was superior to the ZN stain in the presence of a low bacterial load as seen in smears with diagnostic cytomorphological features of tuberculosis. In problem areas like AIE alone or with occasional granulomas, AFB positivity by ZN staining is nearly as good as the fluorescent method, because the bacterial load is high.