Laboratory
Ziehl–Neelsen staining method
Standard laboratory method of staining sputum smears for tuberculosis diagnosis. It involves staining a heat-fixed smear with an aqueous solution of a dye (usually basic fuchsin) containing chemicals (usually phenol) to help the dye penetrate into the cell, washing the smear with acid, alcohol or acid/alcohol and then counterstaining (usually with methylene blue).
Sputum culture conversion
Two consecutive negative cultures from sputa collected at least 25 days apart.
Scanty
In the tuberculosis context, result of examination of a sputum sample when fewer than 10 acid-fast bacilli (AFB) are observed.
Smear conversion
Change from sputum smear-positive to sputum smear-negative.
Interferon-gamma release assay (IGRA)
In-vitro blood tests for cell-mediated immunity to M. tuberculosis that measure interferon-gamma (IFN-γ) released from peripheral blood T-cells or enumerate the number of IFN- producing T-cells following stimulation with synthetic peptides simulating M. tuberculosis proteins.
Drug-susceptibility testing (DST)
In vitro testing using phenotypic methods to determine whether M. tuberculosis is susceptible to a particular drug. Also known as antimicrobial susceptibility testing (AST).
Critical concentration (CC)
The lowest concentration of an anti-tuberculosis drug that will inhibit the growth of 99% of phenotypically wild type isolates of M. tuberculosis complex (MTBC) in vitro.
Acid-fast bacilli (AFB)
Bacteria that do not lose their stain when exposed to acid or acid–alcohol mixture during the staining process, i.e. bacteria of the Mycobacterium tuberculosis complex and all non-tuberculous mycobacteria
Weak positive culture
One to nine colonies of M. tuberculosis detected.
Smear conversion rate
Proportion of treated patients who convert from sputum smear-positive to sputum smear-negative within a specified period of time, usually after 2 or 3 months of the initial phase of tuberculosis treatment. It is not a true rate.
