Diagnosis
Tuberculin skin test (TST)
Intradermal injection of a combination of mycobacterial antigens that elicit an immune response (delayed-type hypersensitivity), represented by induration, which can be measured in millimeters. TST is used to diagnose M. tuberculosis infection.
Tuberculin skin test (TST) reaction
Induration > 5mm for individuals who are at great risk of developing tuberculosis if they become infected with M. tuberculosis. Induration > 10 mm for individuals who have normal or mildly impaired immunity and a high likelihood of being infected with M. tuberculosis but are without other risk factors that would increase their likelihood of developing the disease. Induration >15 mm for individuals with no risk factors for tuberculosis. These cut-offs might be modified depending on the clinical setting or for research purposes.
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).
Tuberculin
Purified protein derivative (PPD) – a mixture of antigens from a culture filtrate extract of M. tuberculosis that is used for skin testing; many of its antigens are non-species specific.
Tuberculin skin test (TST) conversion
A change from a negative test result to a positive test result. The size of the change in the induration needs to be considered, as conversion varies based on the baseline testing results and whether the person has a known exposure to a person with tuberculosis. A TST conversion typically is interpreted as presumptive evidence of new M. tuberculosis infection and poses an increased risk for progression to tuberculosis.
Symptom screen
In the tuberculosis context, procedure in which the patient is asked if they have experienced any signs or symptoms frequently found in persons with tuberculosis.
Systematic screening for tuberculosis
The systematic identification of people with presumptive tuberculosis in a predetermined target group, using tests, examinations, or other procedures that can be applied rapidly.
Screening test, examination, or procedure for tuberculosis
A test, examination or other procedure for tuberculosis that distinguishes people with a high likelihood of having tuberculosis from people who are highly unlikely to have it. A screening test is not intended to be diagnostic. People with positive results on a screening test should undergo full diagnostic evaluation.
Smear conversion
Change from sputum smear-positive to sputum smear-negative.
Scanty
In the tuberculosis context, result of examination of a sputum sample when fewer than 10 acid-fast bacilli (AFB) are observed.
