Sputum microscopy is the main casefinding tool in tuberculosis control programmes. The technique of smear preparation is an important step which needs to be simple for wide applicability. It is often stressed that smear should be prepared from the purulent portions of the sputum as they are likely to have more number of bacilli. It may not be possible for the microscopist/paramedical worker at the periphery to strictly follow this procedure. Hence, a study was conducted to compare the sensitivity of 4 methods of sputum smear preparation viz., direct smear prepared (i) blindly without making any selection of portions of sputum specimen, (ii) from portions of sputum material likely to contain the bacilli, (iii) after mixing up the sputum specimens thoroughly, and (iv) from centrifuged deposit after homogenization of sputum with sodium hydroxide and concentration by centrifugation. Culture was also done for Mycobacterium tuberculosis.

A total of 549 specimens were employed. Positivity rates by four methods were: 79.6% by method (i), 80.3% by method (ii), 80.7% by method (iii) and 77.2% by method (iv). There was no statistically significant difference in the number of positives obtained from different methods. Centrifuged deposit smears proved to be in no way better than the direct smears. The differences in the methods lay only in the classification of positive smear as of a low or high grade.