Making the smear

The National TB Elimination Programme (NTEP) has a standard procedure for sputum smear preparation, the steps for which are listed below:

The tools required for smear preparation include a clean work surface, new and clean glass slides, a discard bucket or a foot-operated bin with a plastic liner, bamboo or wooden applicator sticks or sterile wire loop, spirit lamp and a rack for drying smears.

• Use new, clean, unscratched glass slides and label the slide with the laboratory serial number. 
• Prepare the smear in the centre of the slide covering 3 cm X 2 cm

The smear is prepared by using either a wooden stick (Figure 2) or a sterile wire loop (Figure 3).

Steps for Smear Preparation Using a Wooden Stick

• Break the wooden stick into two halves with uneven ends.

• Using the uneven end, select and pick purulent portions of the sputum specimen and transfer onto a new, clean, labelled, glass slide.

• Using the wooden stick, spread the sputum evenly, in a continuous rotational movement, to cover two-thirds of the central portion of the slide. Smear preparation should be done near a flame. This is required as approximately 6 inches around the flame is considered as a sterile zone which coagulates the aerosols raised during smear preparation.
• Discard the used wooden sticks in the discard bucket or a foot-operated bin with a liner and disinfectant. A different broomstick is used for each smear so that one patient's sputum is not mixed with another patient's sputum.

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• Air-dry the smear slide on the rack for 30 minutes
• After air-drying, heat-fix the smear, using a lighted spirit lamp.

Steps for Smear Preparation Using a Wire Loop

• Take a nichrome wire loop or a disposable loop.

• Using the loop, select and pick purulent portions of the sputum specimen and transfer onto a new, clean, labelled, glass slide.
• Using the loop, spread the sputum evenly, in a continuous rotational movement, to cover two-thirds of the central portion of the slide.

• After use, sterilize the loop in an electric loop sterilizer or flame the loop to red-hot.

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• Air-dry the smear slide on the rack for 30 minutes.
• After air-drying, heat-fix the smear using a lighted spirit lamp.

Resources

• Module for Laboratory Technicians (RNTCP), Central TB Division, MoHFW, 2005.
• Laboratory Diagnosis of Tuberculosis by Sputum Microscopy, GLI Initiative.

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