Table 2.

Bacterial index grading system used to describe the average number of AFB present over 15 hpfs, adapted from the Ridley scoring system used for cases of leprosy in humans.

Bacterial index grade	Bacterial index classification	Average number of AFB/hpf
0	Low	0
1	Low	0.01–0.1
2	Low	0.1–1
3	High	1–10
4	High	10–100
5	High	100–1000
6	High	Over 1000

Abbreviations: AFB, acid-fast bacilli; hpf, high-power field.