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

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.

A comparison of sputum examination for acid fast bacilli By modified cold stain and ziehl-neelsen stain for screening of pulmonary tuberculosis.

A comparative study of the conventional Ziehl-Neelsen (ZN) stain and a new modified cold (MC) stain was carried out to evaluate the efficiency of this staining method in sputum examination for acid fast bacilli (AFB). The MC technique was simplified by avoiding the need for heat and combining the stage of counterstaining to overcome the problem aerosolized phenol and the more laborious heating method. Of the 392 sputum samples examined, 84 were positive and 297 were negative on both staining techniques, with an agreement of 97.2%. In comparison with culture as the gold standard for the diagnosis of tuberculosis, the ZN stain exhibited a sensitivity, specificity, positive and negative predictive values and efficiency of 68.9, 97.4, 92.1, 87.8 and 88.8%, respectively. The same values for the MC stain were 70.6, 97.8, 93.3, 88.4 and 89.5%, respectively with no statistically significant differences (P > 0.05) between the 2 methods. The MC stain was also as reliable as the ZN stain in retaining the color of the stained slide after prolonged storage; an agreement with the first reading was 90% after 4 weeks storage and 80% after 16 weeks storage. The staining reagents had a long shelf life; with agreement between both staining methods of 100% at every time of re-stocking aliquots. To apply this new MC stain for future use at the peripheral level of the health care system, we made a survey by using questionnaires sent to 200 hospitals. Most of the respondants also accepted that the MC stain was easier to perform, more comfortable and much less expensive than the ZN stain. Together, these factors make the MC stain suitable for use as a practical and rapid sputum staining test for screening for patients with pulmonary tuberculosis and for assessment of their treatment.