Table 1 Guidelines of reporting sputum smear microscopy adopted by National Tuberculosis Control Programme in India

IUATLD/WHO scale (1000 × field = HPF*) Grades

Ziehl Neelsen (ZN) microscopy (1000 × magnification: 1 length = 2 cm = 100 HPF)

LED-Fluorescence microscopy (400 × magnification: 1 length = 40 fields = 200 HPF)

Negative

Zero AFB/1 length

Zero AFB/1 length

Positive

Scanty

1–9 AFB/1 length or 100 HPF

1–19 AFB/1 length or 100 HPF

1+ grade

10–99 AFB/1 length or 100 HPF

20–199 AFB/1 length

2+ grade

1–10 AFB/1 HPF on average

5–50 AFB/1 HPF on average

3+ grade

>10 AFB/1 HPF on average

>50 AFB/1 HPF on average