Role of Bleach Concentration Method for Detection of Acid-fast Bacilli (AFB) in Sputum using Conventional Ziehl-Neelsen (ZN) Staining Technique

Sputum microscopy is the most important tool for the detection of Mycobacterium tuberculosis in peripheral laboratories. Sodium hypochlorite concentration technique prior to sputum microscopy may improve the detection of AFB bacilli over direct Ziehl Neelsen's staining method. A prospective study was conducted at Kasturba Medical College, Manipal. Consecutive sputum samples were collected for 3 months. ZN stained smears were made directly of fresh specimens and of specimens that were processed with 3.5% sodium hypochlorite (NaOCl), from each patient. Then, ZN stained smears were observed under light microscopy. A total of 239 samples were collected. The yield of positive smears with ZN staining after NaOCl centrifugation was higher than that with microscopy after direct ZN stain. The percentage increase yield of ZN staining after NaOCl centrifugation over direct ZN staining was 3.3% (8/239). Bleach centrifugation can help in increasing the yield of positivity in sputum smear.