Study of quality of sputum being submitted for smear examination

Background: One of the key factors influencing the results of sputum smear microscopy is the quality of sputum being submitted. Methods: This is a prospective study of quality of sputum specimens being submitted for smear examination under Revised National Tuberculosis Control Programme and its impact on diagnostic yield of sputum smear microscopy. Based on sputum Gram's staining results, the submitted specimen was classified as 'sputum' and 'saliva'. Results: During the period 21 April to 20 June 2012, 238 sputum specimens submitted for evaluation were studied. Of these, 196 (82%) specimens were submitted for diagnosis and 42 (18%) specimens were obtained during follow-up evaluation. Overall, 42/238 (17.6%) specimens were in fact 'saliva' and not sputum. Among specimens submitted for diagnosis (n = 196), 28/167 (16.8%) specimens reported as 'sputum acid-fast bacilli (AFB) negative' were in fact saliva. Among the specimens submitted on follow-up examination (n = 42), 14 of the 38 (36.8%) specimens reported as 'sputum AFB negative' were actually saliva. A significantly higher proportion of sputum smears submitted on follow-up examination were actually 'saliva' as compared to specimens submitted for diagnosis (14/42 [33.3%] vs. 28/196 [14.3%], χ2 = 6.738; P = 0.014). None of the saliva samples were reported to be 'sputum positive'. Conclusions: The fact that a significant proportion of specimens that are reported smear negative are in fact saliva and not sputum highlights the importance of sputum quality in smear microscopy results. Follow-up specimens are more likely to be saliva possibly because directly observed therapy (DOTS) treatment would have resulted in clinical improvements and patients may not be producing significant sputum anymore.