Prevention of False Negative Results During Smear Microscopy
To prevent false negative results during smear microscopy, each laboratory technician needs to:
Prevention of False Positive Results During Smear Microscopy
False positive results can be prevented by using the following measures:
Reporting and Recording results of Smear Microscopy (On paper)
Each Designated Microscopic Center (DMC) needs to maintain a National TB Elimination Program TB (NTEP) Laboratory Register which collects information of all presumptive TB patients who undergo tests or confirmed patients who undergo follow-up tests.
Smear Microscopic Examination: Different Grades of Smear Findings
Different grades of Acid-fast Bacillus (AFB) smear microscopy and its results are as follows:
|
EXAMINATION |
RESULT |
GRADING |
NO. OF FIELDS TO BE EXAMINED |
|---|---|---|---|
|
More than 10 AFB per oil immersion field |
Positive |
3+ |
20 |
|
1–10 AFB per oil immersion field |
Positive
|
2+ |
50 |
Purpose of Acid Fast Bacilli [AFB] Microscopy under NTEP
Tuberculosis is caused by Mycobacterium tuberculosis which is a unique acid-fast gram-positive bacterium.
It is unique because of the high lipid and mycolic acid content of its cell wall. It neither contains the phospholipid outer membrane, nor retains the dye.
Acid-fast Bacilli (AFB) Microscopy identifies tubercule bacilli and hence is used under National TB Elimination Program (NTEP) for: