Introduction: Reports indicate that fluorescent staining of smears increases sensitivity of direct microscopy;so ZN staining is being replaced with fluorescent microscopy in RNTCP in India. Chemical processing and spu...Introduction: Reports indicate that fluorescent staining of smears increases sensitivity of direct microscopy;so ZN staining is being replaced with fluorescent microscopy in RNTCP in India. Chemical processing and sputum concentration may also improve sensitivity of microscopy. Objective: To compare the sensitivity and specificity of microscopy for AFB using ZN and fluorescent stains in direct and concentrated specimen with culture as gold standard. Methods: Morning sputum specimen of patients, suspected of having pulmonary tuberculosis, over a period of 6 months was subjected to direct microscopy using fluorescent stain;the same slide was over-stained with ZN stain. Same sputum sample was concentrated by Petroff’s method and subjected to fluorescent microscopy followed by ZN microscopy and finally to culture for AFB. Results: Sensitivity of fluorescent stained concentrated sputum samples was maximum and of ZN stained unprocessed sputum samples was minimum. Specificity of three of the methods was equal at 0.96 but of ZN stained concentrated sputum smears was 0.97. Sensitivity of total fluorescent stains was 0.85 (Specificity 0.96) and sensitivity of total ZN stained smears was 0.80 (Specificity 0.96). Discussion: We used same smear for fluorescent and ZN stains, so smear related variability is decreased. Blinding for microscopy was practically complete. Conclusion: The sensitivity of sputum microscopy for AFB can be increased by concentrating the sputum and using fluorescent microscopy. The specificity remains high in all the methods.展开更多
Background and objectives: With 2.2 million new cases every year, Tuberculosis (TB) continues to be an epidemic of large proportions in India. Conventional direct sputum smear microscopy, though limited in its sensiti...Background and objectives: With 2.2 million new cases every year, Tuberculosis (TB) continues to be an epidemic of large proportions in India. Conventional direct sputum smear microscopy, though limited in its sensitivity, is still the most common method of testing for TB. Newer techniques such as concentrated sputum microscopy, have shown some promise in improving this limited sensitivity. We have compared the efficacy of concentrated sputum versus the direct smear technique in 1000 sputum samples of patients suspected to be suffering from TB. Methods: A total of 1000 sputum specimens were collected for direct acid-fast bacilli (AFB) smear, concentrated AFB smear and culture from St. John’s Medical College and Hospital. 39 contaminated samples were (3.9%) omitted during the final analysis. Mycobacterial culture was used as the reference standard method for the detection of TB. Results: 184 and 198 of the 961 samples were found to AFB positive by direct smear microscopy and concentrated smear technique respectively. The measured sensitivity and specificity of direct smear microscopy were 69.86% and 95.82%, while that of concentrated smear microscopy was 76.71% and 95.96 % respectively. 33 samples found to be negative by the direct smear method turned out to be positive by the concentrated smear technique. Conclusions: Though our study suggests no significant statistical difference between the two techniques of detecting pulmonary tuberculosis, we recommend the use of the concentrated technique in centres such as ours, where facilities are already in place. In this way, the number of cases of TB that remain untreated may significantly come down.展开更多
文摘Introduction: Reports indicate that fluorescent staining of smears increases sensitivity of direct microscopy;so ZN staining is being replaced with fluorescent microscopy in RNTCP in India. Chemical processing and sputum concentration may also improve sensitivity of microscopy. Objective: To compare the sensitivity and specificity of microscopy for AFB using ZN and fluorescent stains in direct and concentrated specimen with culture as gold standard. Methods: Morning sputum specimen of patients, suspected of having pulmonary tuberculosis, over a period of 6 months was subjected to direct microscopy using fluorescent stain;the same slide was over-stained with ZN stain. Same sputum sample was concentrated by Petroff’s method and subjected to fluorescent microscopy followed by ZN microscopy and finally to culture for AFB. Results: Sensitivity of fluorescent stained concentrated sputum samples was maximum and of ZN stained unprocessed sputum samples was minimum. Specificity of three of the methods was equal at 0.96 but of ZN stained concentrated sputum smears was 0.97. Sensitivity of total fluorescent stains was 0.85 (Specificity 0.96) and sensitivity of total ZN stained smears was 0.80 (Specificity 0.96). Discussion: We used same smear for fluorescent and ZN stains, so smear related variability is decreased. Blinding for microscopy was practically complete. Conclusion: The sensitivity of sputum microscopy for AFB can be increased by concentrating the sputum and using fluorescent microscopy. The specificity remains high in all the methods.
文摘Background and objectives: With 2.2 million new cases every year, Tuberculosis (TB) continues to be an epidemic of large proportions in India. Conventional direct sputum smear microscopy, though limited in its sensitivity, is still the most common method of testing for TB. Newer techniques such as concentrated sputum microscopy, have shown some promise in improving this limited sensitivity. We have compared the efficacy of concentrated sputum versus the direct smear technique in 1000 sputum samples of patients suspected to be suffering from TB. Methods: A total of 1000 sputum specimens were collected for direct acid-fast bacilli (AFB) smear, concentrated AFB smear and culture from St. John’s Medical College and Hospital. 39 contaminated samples were (3.9%) omitted during the final analysis. Mycobacterial culture was used as the reference standard method for the detection of TB. Results: 184 and 198 of the 961 samples were found to AFB positive by direct smear microscopy and concentrated smear technique respectively. The measured sensitivity and specificity of direct smear microscopy were 69.86% and 95.82%, while that of concentrated smear microscopy was 76.71% and 95.96 % respectively. 33 samples found to be negative by the direct smear method turned out to be positive by the concentrated smear technique. Conclusions: Though our study suggests no significant statistical difference between the two techniques of detecting pulmonary tuberculosis, we recommend the use of the concentrated technique in centres such as ours, where facilities are already in place. In this way, the number of cases of TB that remain untreated may significantly come down.
