Effect of washing sputum on detection of pneumococcal capsular antigen.

The effect of washing of sputum on detection of pneumococcal capsular antigen was investigated. A total of 357 sputa from 104 patients was tested. Antigen could be detected in 164 (46%) of the sputa in both the washed and unwashed portions, and could not be detected in either portion in a further 180 (50%) sputa. Four (1%) of the sputa agglutinated in the negative control, and were considered to be auto-agglutinating. In 9 (3%) sputa antigen could be detected in the unwashed portion, but not in the washed portion. There were no specimens in which antigen could be detected in the washed portion only. These data indicate that pneumococcal capsular antigen can be detected as reliably in washed sputum as in unwashed sputum.