Evaluation of sputum staining by modified cold method and comparison with Ziehl-Neelsen and fluorochrome methods for the primary diagnosis of tuberculosis.

ABSTRACT

An improved acid-fast staining technique for sputum examination for the primary diagnosis of tuberculosis is described. The technique was modified and simplified by the elimination of heating and by combining the stages of counterstaining making the technique easier and safer, with less risk of phenol aerosols. The efficiency of this method was evaluated by comparison with two conventional methods, Ziehl-Neelsen (ZN) staining and fluorochrome staining; culture was deemed the gold standard for tuberculosis diagnosis. Of the 392 sputum samples examined, 22.7%, 19.4% and 22.9% were positive by the ZN, fluorochrome and modified cold (MC) staining methods respectively. In comparison with culture results, the sensitivities of ZN, fluorochrome and MC methods were 68.9%, 59.7% and 70.6% respectively; the specificities were 97.4%, 98.2% and 97.8% respectively and the efficiencies were 88.8%, 86.5% and 89.5% respectively. The fluorochrome method was statistically less sensitive than the ZN and MC (p < 0.05), but no significant differences between the ZN and MC were found (p > 0.05). The results of the MC and ZN methods were in close agreement (97.2%); the slides stained by these techniques could be stored for a long time and the staining reagents were stable for several weeks. In conclusion, the MC method proved to be a valuable alternative to ZN staining for the primary diagnosis of tuberculosis.