The Morphological Index (MI) is a semiquantitative measure of the effectiveness of a therapy in a patient with leprosy. A mycobacterium that is completely intact is presumed to be viable.
Parameters:
(1) total number of mycobacteria counted
(2) number of acid fast bacilli that are perfectly intact
morphological index in percent =
= (number of mycobacteria that are acid fast and intact) / (total number counted) * 100%
Interpretation:
• The morphological index should become very low then negative once effective therapy has been initiated.
• A stable or increasing MI suggests antibiotic resistance or nonadherence to therapy.
Limitations:
• There is considerable inter-observer variability.
• Counting can be difficult if only small numbers are present.
• Careful staining is needed for reproducible results.
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