The Art of Sputum Expectoration for TB Diagnosis

January 22, 2013

Specimen quality is paramount for accurate laboratory, and therefore clinical diagnosis. The old adage “garbage in, garbage out” is true, for tuberculosis diagnosis too. Tuberculosis specimen quality criteria are outlined in the Guide to Services entry “Mycobacterium tuberculosis”, but this only outlines the requirements for the product of sputum expectoration i.e. sample should contain mucoid or mucopurulent material and the volume should be at least 5 ml etc.   There is also the art of successfully obtaining said product, and this entails taking time to explain to the patient what a good deep expectoration is (versus saliva or nasopharyngeal secretions) and why this is important. The best practice is to observe the expectoration, at least until the first successful sputum is produced, so that one has the opportunity to guide the process which will serve as a “training” session with the patient for when one is not present at the time of the second and third specimen production. Adequate education of TB suspects by the health care provider has been shown to result in a substantial increase in the quality of the sample, the number of positive samples and the density of acid fast bacilli (AFB) per sputum slide.   The following illustration is taken from the Provincial Disease Control Manual        


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