Sputum Smear Preparation: Selecting the Best Portion of the Sputum Specimen for Microscopy

While doing sputum smear microscopy for presumptive TB patients, it is essential that the correct specimen part is tested for microscopy.

During smear preparation, each Laboratory Technician (LT) should identify a part of specimen that is either mucoid or purulent or mucopurulent, instead of thin saliva (Figure).

Acid-fast Bacilli (AFB) tend to be more in the purulent part of the smear.

Figure: Best Portion Selection for Performing Sputum Microscopy

The patient often provides saliva instead of sputum sample which results in false negative test results. Hence, counselling and guidance is of immense importance to get good quality sputum for proper diagnosis.

Resources

• Laboratory Diagnosis of Tuberculosis by Sputum Microscopy, WHO, Global Laboratory Initiative, 2013.

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