144 / 276
Reading
Keep stained smears in the dark (box or folder), and read on the same day of
staining as the fluorescence is prone to fading with time.
To be able to focus with ease, better to read first a positive control smear stained
by auramine O
Use the objective 20x for focusing and read the slide using 40X objective (avoid
using oil and immersion 100X objective, inexperienced readers should ask
confirmation from a supervisor)
Scan the stained smear systematically from one side to the other, for one length
of the smear
Acid-fast bacilli appear bright yellow against the dark background material.
Store the slides in a slide box following the Laboratory Register Number as they
will be needed for EQA. Do not write the result on the slide.
Grading of smears
The table below depicts information on grading and the number of fields to be
examined in different situations:-
200-250x magnification:
1 length = 30 fields = 300
HPF
400x magnification:
1 length = 40 fields = 400
HPF
Grading
Result
No AFB per 1 length
No AFB per 1 length
0
Neg
1-29 AFB per 1 length
1-19 AFB per 1 length
Scanty*
Pos
30-299 AFB per 1 length
20-199 AFB per 1 length
1+
Pos
10-100 AFB per 1 field on
average
5-50 AFB per 1 field on
average
2+
Pos
More than 100 AFB per 1
field on average
More than 50 AFB per 1 field
on average
3+
Pos
137