The collection of good sputum specimens is an art in itself and has been described in other books,2 Examination of a badly collected sputum specimen can give misleading results because of contamination with the normal bacterial flora present in the mouth and throat; “sputum” consisting of saliva and food particles should not be examined.
2 See, for example: Manual of basic techniques for a health laboratory, Geneva, World Health Organization, 1980; and Technical guide for sputum examination for tuberculosis by direct microscopy. Bulletin of the International Union Against Tuberculosis and Lung Diseases, Suppl. 2, 1978.
The sputum should be collected in a sterile wide-mouthed container with a secure, tight-fitting cover and sent to the laboratory without delay. If the sputum is allowed to stand after collection, overgrowth of contaminating bacteria may take place before the examination is carried out and the results of smears and cultures will be highly misleading. For this reason, it is not generally permissible to send sputum specimens to the laboratory by mail. The only exceptions are specimens for tuberculosis examination that may have to be sent to a district or regional laboratory. The local and national postal regulations for the transmission of infected (pathological) material must be strictly applied.