How do you Diagnose Drug-Resistant Tuberculosis?

Tuberculosis can be detected by several types of tests. Some tests help in diagnosing TB, whereas some tests help to detect if the TB bacterium is susceptible to TB drug treatment. If the bacteria are susceptible or vulnerable to treatment, one can expect positive treatment results. If the bacteria are resistant to treatment, it is drug resistant bacteria. The TB test which helps in finding if a person has drug resistant TB, is known as the drug susceptibility test.


TB tests take a long time to yield results. Some tests are not very accurate and some have low sensitivity or specificity. These can lead to “false negative” results.

1. TB culture test is the most accurate TB test. It involves evaluating the sputum sample; however, it can take several weeks to get results.

2. TB skin test: This test involves injecting a liquid, tuberculin, under the skin in the arm. The response to this test is observed between 48 to 72 hrs. If response is seen as a swelling or hard area, it is positive test and indicates the person is infected with TB bacteria. This test is also known as Mantoux test; however, this test can give false results.

3. TB Interferon Gamma Release Assays (IGRAs): This is a new and accurate type of test. It is a blood test that measures immune response of a person to the TB causing bacteria. There are two types of IGRA tests - QuantiFERON TB Gold Test and the T-Spot TB test.

4. TB Molecular tests: These are new tests and are relatively expensive compared to the other tests.

  • GeneXpert test: This is a test which detect if the presence of TB bacterium as well as its resistance to Rifampicin. Sputum sample is used and results are received in less than 2 hours
  • TrueNat TB test: This is a newer molecular test which gives results in about 1-2 hours. It detects the presence of TB bacteria as well as its resistance for the drug Rifampicin

5. Chest X-ray: This helps to diagnose clinically active TB infection

References:

  1. Drug-Resistant TB - (https://www.cdc.gov/tb/topic/drtb/default.htm)
  2. Drug-Resistant Tuberculosis - (https://www.tbalert.org/about-tb/global-tb-challenges/drug-resistant-tb/)
  3. What Is Multidrug and Extensively Drug Resistant TB? - (https://www.lung.org/lung-health-and-diseases/lung-disease-lookup/tuberculosis/drug-resistant-tb.html)
  4. Drug Resistance Mechanisms in Mycobacterium tuberculosis - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4790366/)
  5. Non-Steroidal Anti-inflammatory Drugs As Host-Directed Therapy for Tuberculosis: A Systematic Review - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5492311/)
  6. What is multidrug-resistant tuberculosis (MDR-TB) and how do we control it? - (http://www.who.int/features/qa/79/en/)

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