False Positivity and False Negativity in Microscopy

False result: It’s a situation where the test result is different from the truth.

Types of False Results

• False Positive: When the test result is positive but the patient does not have TB.
• False Negative: When the test result is negative but the patient has TB.

Both cases will lead to wrong categorization and incorrect treatment. The consequences of false results are shown in the figure below:

Figure: Consequences of False Results in Sputum Smear Microscopy; Source: Quality Assurance of Sputum Microscopy in DOTS Programmes.

Resources

• RNTCP Module for Laboratory Technicians, CTD, MoHFW, 2005.
• Quality Assurance of Sputum Microscopy in DOTS Programmes Regional Guidelines for Countries in the Western Pacific, WHO, 2003.

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