The Bacteriological Index (BI) is a means of estimating the bacterial load for a patient with leprosy. It is a logarithmic scale that is fairly simple to perform.
Specimen: skin slit smear with acid-fast stain that has been partially decolorized
Parameters:
(1) number of bacteria counted
(2) number of microscopic fields examined under oil immersion (1000x magnification)
Number of Bacteria
Number of Fields
BI
>= 1
100
1+
>= 1
10
2+
>= 1
1
3+
>= 10
1
4+
>= 100
1
5+
>= 1,000
1
6+
Limitations:
• There may be some variability in site selection, smear preparation and slide examination. This is somewhat compensated for by the 10 fold change between levels.
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