A persistent cough lasting more than two weeks, coughing up blood or discoloured sputum, and unexplained weight loss can all be signs of tuberculosis (TB). Sometimes, a person may not even know whether they’re infected as the disease can be asymptomatic or inactive. This is known as latent TB infection, where the bacteria remain dormant in the body without causing active disease. Speaking with the Only My Health team, Dr Ashish Bajaj, Consultant Microbiologist, Oncquest Pathlabs, Gurugram, discusses the range of tests one can take to diagnose TB early.
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How Long Can You Have TB Without Knowing?
Every year, TB accounts for one crore cases worldwide, says the World Health Organization (WHO), adding that although it is a preventable and curable disease, 10.5 lakh people still die from TB each year.
The US Centers for Disease Control and Prevention (CDC) suggests that many people who have latent TB infection never develop TB disease. While some people develop TB disease soon after becoming infected (within weeks), others may get sick years later when their immune system becomes weak for another reason.
So how do you know if you are infected?
Important Tests To Take
To diagnose tuberculosis, a range of tests can help:
Tuberculin Skin Test (TST)
The TST, also called the Mantoux test, involves injecting a small amount of tuberculin purified protein derivative (PPD) into the skin. A positive reaction indicates exposure to the tuberculosis bacterium but does not differentiate between latent infection and active disease. Newer Mtb antigen-based skin tests (TBST) have been developed to measure the cell-mediated immunological response to Mtb specific antigens.
Interferon-Gamma Release Assays (IGRAs)
IGRAs are blood tests that are based on the lymphocyte response to M. tuberculosis-specific antigens (ESAT-6 and CFP-10). These tests are more specific than TST.
Smear Microscopy
This test examines samples under a microscope to identify acid-fast bacilli (AFB), which are characteristic of tuberculosis. It is primarily used for diagnosing pulmonary tuberculosis.
Culture and Drug Sensitivity Testing
Mycobacterial culture involves growing M. tuberculosis from a clinical specimen, confirming the presence of the bacteria. Drug sensitivity testing helps determine which antimicrobial drugs are effective against the specific strain of tuberculosis, aiding in appropriate treatment selection.
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Molecular tests
Cartridge Based Nucleic Acid Amplification Test (CBNAAT) is a molecular assay, which permits rapid TB diagnosis through detection of the DNA of Mycobacterium tuberculosis. Line probe assay(LPA) and TB PCR can help in detection of drug resistance due to mutation in genes.
Imaging Studies
Chest X-rays, computed tomography (CT) scans, and magnetic resonance imaging (MRI) can be used to detect pulmonary and extrapulmonary manifestations of tuberculosis. They help visualise lung infiltrates, lymph node enlargement, bone destruction, or other organ involvement.
Biopsy and Histopathological Examination
In cases of suspected extrapulmonary tuberculosis, a biopsy may be performed to obtain a sample from the affected organ or tissue. Histopathological examination of the biopsy sample can reveal characteristic granulomas, caseous necrosis, and presence of acid-fast bacilli.
Bottomline
TB is an infectious disease. It is important to diagnose it early so as to get timely and effective treatment. It is a preventable disease and if caught early, can be cured. Ensure that you consult a doctor if you have a cough that lasts more than two weeks and get your tests.