How do they diagnose TB?
1. Medical History and Physical Examination:
- Doctors inquire about symptoms, such as persistent cough, fever, night sweats, and weight loss.
- A physical exam may reveal signs like lung abnormalities or swollen lymph nodes.
2. Sputum Smear Microscopy:
- This is a common initial diagnostic test for TB.
- Patients cough up sputum (phlegm from the lungs) into a container.
- The sputum sample is smeared onto a glass slide, stained, and examined under a microscope for the presence of acid-fast bacilli (AFB), which are TB bacteria.
3. Sputum Culture:
- If AFB are detected in the sputum smear, or if there is a strong suspicion of TB, a sputum culture is performed.
- The sputum sample is cultured in a laboratory to grow TB bacteria, allowing for identification of the specific bacterial strain and its antibiotic susceptibility profile.
4. Chest X-ray:
- An X-ray of the chest can reveal abnormalities in the lungs, such as the presence of nodules, infiltrates, or cavities, which may suggest TB infection.
5. Tuberculin Skin Test (Mantoux Test):
- This test involves injecting a small amount of tuberculin (a protein derived from the TB bacteria) into the skin.
- After 48-72 hours, the injection site is examined for a raised, hardened area (induration), indicating a positive reaction. A positive tuberculin skin test suggests previous exposure to TB bacteria, but it doesn't necessarily mean active infection.
6. Interferon-Gamma Release Assay (IGRA):
- Similar to the tuberculin skin test, IGRA blood tests (e.g., QuantiFERON-TB Gold, T-SPOT.TB) measure the immune response to TB antigens.
- A positive IGRA result suggests TB infection, but further tests may be needed to determine if it's active or latent TB.
7. Molecular Tests (PCR):
- Polymerase chain reaction (PCR) tests can detect TB bacteria's genetic material (DNA) in sputum or other samples.
- PCR tests can rapidly identify TB and provide information about certain genetic mutations that affect drug susceptibility.
8. Biopsy:
- In some cases, a biopsy of affected tissue (e.g., lymph node, lung tissue) may be necessary to diagnose TB.
- A tissue sample is collected and examined under a microscope for the presence of TB bacteria or granulomas (collections of immune cells that form in response to TB infection).
A combination of tests and clinical findings is typically used to confirm a diagnosis of TB, and further diagnostic procedures might be required in certain situations.