Test for Diagnosis of Tuberculosis

Tuberculosis is caused by Mycobacterium tuberculosis bacteria. It primarily affects the lungs but may involve other body parts. Several tests can be used to diagnose tuberculosis (TB), depending on the suspected site of infection. Read on to know more.

Screening Tests for Tuberculosis

This includes:

1. Tuberculin skin test (TST):

Also known as the Mantoux test, this test involves injecting a small amount of purified protein derivative (PPD) tuberculin into the skin of the forearm. The doctor will then check the injection site 48 to 72 hours for a raised, red bump, indicating a positive reaction.

2. Interferon-gamma release assays (IGRAs):

These blood tests measure the release of interferon-gamma by T-cells in response to specific TB antigens. Most health regulatory bodies recommend screening for specific high-risk populations, including:

• Those who spent time with the individual suffering from infectious TB.

• Individuals with HIV or with immune system disorders.

• The most recent immigrants from the regions with high TB incidence

Diagnostic Tests to Determine Active TB Disease vs. Latent TB Infection

If screening tests are positive, further testing is needed:

• Chest X-ray

Helps locate lung abnormalities and lesions caused by active TB.

• Sputum smear microscopy

Here, a sputum sample can detect the presence of actual TB bacteria under a microscope, which confirms active TB disease.

• Nucleic Acid Amplification Test

A quick method of identifying TB-causing bacteria in the lab by amplifying their DNA.

Why Testing for HIV Is Recommended When TB Is Diagnosed?

People with HIV have a very high chance of getting active TB. AIDS can tear down the immune system. WHO says HIV testing is mandatory with any diagnosis of TB. If the patient has both HIV and TB, doctors should decide the treatment plan accordingly, as both diseases and medications may interact with each other.

Starting Treatment for Tuberculosis After Diagnosis

If the tests show active TB, the standard treatment protocol is a 6-month course of multiple antibiotics to stop the growth and kill TB bacteria. Premature treatment discontinuation can give rise to drug resistance and TB recurrence.

Conclusion

Ranging from screening tests to identification of infection or active disease, accurate testing is the key to early diagnosis and treatment of TB. The choice of diagnostic test(s) depends on several factors and in many cases, a combination of tests may be used to establish a diagnosis of TB.

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Source: cdc.gov, tbcindia.gov.in, lung.org

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