مقایسه روش های میکروسکوپی فلورسنت و زیل - نلسن در تشخیص باسیل مقاوم به اسید و الکل

Background and Aim: Nowadays new methods are used to detect TB. But due to their costs and technological limitations for all, we compare two old staining methods, Ziehl-Neelsen (ZN) and fluorescence, and their diagnostic values in detection of TB. Materials and Methods: This descriptive analytical study was done in two steps. First, 1430 patients of suspected having TB who were referred to central TB laboratory of Birjand and 3125 specimens were collected between April 1995 and April 2002. These specimens were stained by carbolfuchsin (Ziehl-Neelsen) and auramin – 0 (fluorochorom) to detect acid fast bacilli (AFB). In the second step 500 patients out of 1430 cases were studied applying ZN and FM methods. Among these, 30 cases of FM and 26 cases of ZN had positive smear. On the whole, 37 cases were positive, using either method. The gathered data were analyzed by means of kappa agreement multiplex statistical test. Results: In this study 116 patients (8.1%) were smear positive with fluorescence microscopy (FM) and 41 patients of this group (2.9%) were also positive with ZN. ZN staining showed 35% sensitivity in positive FM specimens. When the first and second specimens, were simultaneously studied, sensitivity of ZN rose from 35% to 42%. The 500 patients were studied with both ZN and FM. 30 specimens were positive with FM, and 26 were positive with ZN, and in addition 37 specimens were positive with both techniques. Agreement multiplex kappa for these detective methods-ZN and FM- was 0.660 (P<0.001). In this study by setting FM as a basement, ZN sensitivity was 77.3%, specificity was 98.5%, positive predictive value 85%, and negative predictive value 97.6%. Conclusion: These results showed that due to high agreement between ZN and FM, both FM and ZN methods have detective value for the diagnosis of TB, but when only one specimen is available, FM is preferred. So, we suggest that, where possible, suspected specimens are first stained by FM [to improve velocity and sensitivity] then positive specimens be checked with ZN staining.