Prevention of Some Common Issues Encountered During Smear Microscopy at the DMC

Operational conditions, including the safety of the laboratory and personnel, adequate laboratory supplies are important in sputum smear microscopy.

The manpower should be adequately trained to perform sputum smear microscopy.

The designated microscopy centre (DMC) should have quality aspects in place, follow internal quality control measures and should be covered under external quality assurance (EQA) under NTEP.

To avoid common issues, it is important to ensure the following:

Operational aspects:

• Ensure availability of adequate reagents, consumables and well-functioning equipment for sputum smear microscopy
• Space and layout of the DMC should be in accordance with NTEP guidelines
• Availability of trained manpower
• Availability of water
• Follow laboratory biosafety measures including air borne infection prevention
• Follow biomedical waste management procedures and guidelines
• DMC should be supervised by a higher laboratory

Technical aspects:

• Label sputum containers, slides, and laboratory forms accurately
• Label the walls of the sputum containers and not the lid
• All sputum containers should be used only once
• Make sure there are no food particles in the sputum sample
• Always use new, unscratched slides
• Use a separate wooden stick for each sample
• Select thick, purulent portion to make the smear
• Prepare smears correctly-not too thick, too thin or too little material
• Slides should be air-dried, do not use a flame to dry slides
• Fix the slide for the correct length of time, not too short or too long
• Always use filtered carbol fuchsin
• Do not allow the carbol fuchsin to dry during staining, do not allow the carbol fuchsin to boil
• Decolourize adequately with sulphuric acid
• Never examine a slide while it is wet as examining a wet slide may damage the microscope
• Never allow the oil immersion applicator to touch a slide
• Never allow the oil immersion lens to touch a slide
• Examine every smear for at least five minutes before recording it as negative
• Cross-check the label on the laboratory form and sputum container before recording
• Clean the lens after reading the slides so that the microscope remains in good working condition
• Never use spirit or alcohol to clean the lens, use lens paper
• Store microscope properly to prevent fungal growth

Quality aspects:

• The laboratory technician should prevent both false-negative and false-positive results
• Collect good quality sputum samples
• Follow internal quality control for reagents and staining procedures
• Reagents should be used within the expiry period
• The microscope should be covered under an annual maintenance contract
• Record and report the results accurately
• DMC should participate in EQA for sputum smear microscopy

Resources

• Laboratory Diagnosis of Tuberculosis by Sputum Microscopy
• Guidelines for Quality Assurance of smear microscopy for diagnosing tuberculosis

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