If someone has tuberculosis, the tuberculosis bacteria are examined more closely in the laboratory. If the tests show that the medication is effective against the tuberculosis bacteria, the pathogen is referred to as drug-sensitive or drug-susceptible.

Initially, the four standard drugs that are usually used for treatment are tested: Isoniazid, rifampicin, pyrazinamide and ethambutol. If a drug is not sufficiently effective against the bacteria, this is referred to as resistance and the drug in question cannot be used.

These tests, also known as susceptibility or resistance tests, are important in order to quickly determine the best possible therapy. If resistance is present, the treatment of tuberculosis becomes more complicated, as the proven standard therapy can then no longer be used.

Thanks to modern molecular genetic testing methods, the first results of these tests are often available after just a few days. However, confirmation by longer-lasting culture methods is still necessary.