Comparison between direct smear by Ziehl-Neelsen and concentrated smear by fluorochrome stain

Abstract

For the purpose of supporting more completely our assertion that two times concentrated sputum smear tests by fluorochrome stain are more sensitive than or at least equal to 3 times direct smear tests by Ziehl-Neelsen stain, we compare the sensitivity of concentrated smear by stain (conc-smear) and direct smear by Ziehl-Neelsen stain (di-smear). Retrospective study of sputum acid-fast smear tests in our hospital with tuberculosis ward from Jan. 1, 2003 to Sep. 30, 2005. 170 of 899 sputums on which both conc-smear and di-smear were done, were smear positive by at least one of the two smear method. Of those 170, 167 (98.2%) were positive by conc-smear and 113 (66.5%) were positive by di-smear, and the difference was statistically significant (p<0.001). Of those 110 that were positive by both conc-smear and di-smear, in 65 (59.1%) smear grade by conc-smear were higher than that of di-smear, and in 3 (2.7%) smear grade by di-smear were higher than that of conc-smear. Smear grades in conc-smear were significantly higher than that of di-smear (p< 0.001). In sensitivity and smear grades, conc-smear was superior to di-smear. Together with previous report, 2 times conc-smear tests are supposed to be superior to 3 times di-smear.