Laboratory parameters of the 1st order – obligatory laboratory tests.
- Tuberculin skin test* * (THT) – this procedure involves injecting purified tuberculin into the skin; the test cannot distinguish between old and fresh infection. The test is recommended for children younger than 5 years of age and may also be used in children between 5 and 14 years of age.[False-positive results occur in patients who have previously received BCG vaccination or have otherwise been exposed to mycobacteria; false-negative results are possible in patients who have immune-mediated inflammatory diseases or are taking immunosuppressants]
- Interferon-gamma release assay (synonyms: γ-interferon assay; interferon-gamma release assay, IGRA) The test should preferably be used in adolescents aged 15 years and older and adults; is also considered suitable for tuberculosis screening (TB screening), e.g., before administration of TNF-α inhibitors in rheumatic. Diseases.[Specificity (probability that actually healthy people who do not have the disease in question are also detected as healthy in the test) for the detection of latent tuberculosis is higher than in the tuberculin skin test; the test result is not affected by a previous BCG vaccination].
- Bacteriological examination* (microscopic and cultural): sputum (morning sputum), tracheal secretion, gastric juice (3 samples on 3 consecutive days); urine, lymph nodes, other tissue (if necessary bronchoscopic material / material obtained by pulmonary lavungungl: bronchoalveolar lavage, protected brush, transbronchial biopsy); cultural detection takes 3 to 8 weeks.
- Molecular genetic methods (Tbc-PCR)* – this test method is based on the recognition of the genetic material of the pathogens; fastest detection: < 24 h.
- Resistogram (susceptibility testing)* – this procedure is performed to detect possible resistance of pathogens to various antibiotics (drugs against bacterial infections).
- Differential blood count* * [monocytosis]
- HIV diagnostics – to exclude an HIV-coinfected tuberculosis patient (esp. southern Africa).
Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.
- Determination of the species of pathogens* .
- Molecular typing* – also used to determine pathogen species.
* The direct detection of the pathogens “Mycobacterium tuberculosis/africanum, Mycobacterium bovis” is reportable under the Infection Protection Act (IfSG). Subsequently, the result of the resistance determination must also be reported; in advance also for the detection of acid-fast rods in the sputum.* Caution! Conventional tuberculosis tests for sputum fail in children.* * Tuberculin test in combination with a differential blood count is suitable to detect the transition from latent to active tuberculosis: highly positive tuberculin skin test with a diameter of the infiltrate ≥ 14 mm and additional monocytosis resulted in a hazard ratio of 8.46 (confidence interval 1.74 – 41.22).
Tolerance ranges for hepatic elevations during antituberculous therapy
Discontinuation of therapy if exceeded
| Baseline value before therapya | Laboratory parameters | Tolerance rangea | Tolerance range for symptomsb |
| < 2-fold | AST (GOT) | up to 5-fold | up to 3-fold |
| ALT (GPT) | up to 5-fold | up to 3-fold | |
| Bilirubin | up to 2-fold | no tolerance range |
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