Induration Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Induration and links to relevant pages within the course.
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| Records and Results Skin tests are read 48-72 hours after injection by a trained health-care worker such as a physician or nurse.The diameter of any induration is measured in millimeters.Records of the test are kept in the individual's health record for future reference. | View Page |
| TST Interpretation and Classification The TST interpretation depends on the measured diameter of the induration and the clinical status of the patient.An induration of 15 or more millimeters is considered positive in all persons.An induration of 10 or more millimeters is considered positive in patients in the high risk progression groups and in mycobacteriology laboratory workers.An induration of 5 or more millimeters is considered positive in the high risk infection groups. | View Page |
| False Positive TST reactions A false positive reaction is a TST induration >5 millimeters even though the person is not infected with Mycobacterium tuberculosis. Some causes are:
previous BCG vaccination,infection with nontuberculosis mycobacteria,incorrect TST administration or interpretation. | View Page |
| TST False Negative Reactions A false negative reaction is no induration after a TST even if the person is infected with Mycobacterium tuberculosis. Some causes of this are: weakened immune system,recent, old or overwhelming TB infection,immature immune system (<6 months of age),some viral illnesses,recent live-virus vaccinations,incorrect TST administration or interpretation. | View Page |