What to do with a positive Quantiferon (QFT) result indicating latent tuberculosis (TB) infection?

From the Guidelines

A positive Quantiferon (QFT) test indicates latent tuberculosis infection (LTBI) and requires medical evaluation and likely treatment to prevent progression to active TB disease. First, active TB must be ruled out through symptom assessment, chest X-ray, and possibly sputum tests. If LTBI is confirmed, treatment should be initiated with one of several regimens: 3 months of once-weekly isoniazid plus rifapentine (3HP), 4 months of daily rifampin (4R), or 9 months of daily isoniazid (9H) 1. The 3HP regimen consists of isoniazid (15 mg/kg, max 900 mg) plus rifapentine (600-900 mg based on weight) weekly for 12 weeks. The 4R regimen uses rifampin 10 mg/kg daily (max 600 mg) for 4 months. The 9H regimen uses isoniazid 5 mg/kg daily (max 300 mg) for 9 months, with vitamin B6 (25-50 mg) to prevent peripheral neuropathy.

Some key points to consider:

• Shorter regimens like 3HP or 4R are generally preferred due to better completion rates 1.
• Regular monitoring for medication side effects is essential, particularly liver function tests for those with risk factors.
• Treatment is especially important for individuals with recent TB exposure, HIV infection, immunosuppression, or other conditions that increase the risk of progression to active TB.
• Treating LTBI reduces the risk of developing active TB disease by 60-90%, preventing both individual illness and community transmission 1.

It's also important to note that the QuantiFERON-TB Gold test has been approved by the FDA as an aid for diagnosing M. tuberculosis infection, and its use is recommended in certain circumstances, such as contact investigations and evaluation of recent immigrants 1. However, the test's ability to predict who will eventually develop TB disease has not been determined, and further research is needed to fully understand its utility in clinical practice 1.

From the FDA Drug Label

Isoniazid is recommended as preventive therapy for the following groups, regardless of age... Candidates for preventive therapy who have HIV infection should have a minimum of 12 months of therapy. Candidates for preventive therapy who have fibrotic pulmonary lesions consistent with healed tuberculosis or who have pulmonary silicosis should have 12 months of isoniazid or 4 months of isoniazid and rifampin, concomitantly.

With a positive Quantiferon (QFT) result indicating latent tuberculosis (TB) infection, preventive therapy is recommended. The preferred treatment options include:

• Isoniazid for at least 12 months, especially for those with HIV infection or fibrotic pulmonary lesions consistent with healed tuberculosis 2
• Alternatively, 4 months of isoniazid and rifampin may be considered for certain individuals, such as those with pulmonary silicosis 2 It is essential to consult a healthcare professional to determine the best course of treatment based on individual risk factors and medical history.

From the Research

Next Steps After a Positive Quantiferon Result

A positive Quantiferon (QFT) result indicates latent tuberculosis (TB) infection. The following steps can be considered:

• Consult a healthcare provider to discuss the results and determine the best course of action 3, 4
• Undergo a medical evaluation to rule out active TB disease, which may include a physical examination, chest X-ray, and sputum tests 5, 6
• Consider treatment for latent TB infection, especially if recently infected or at high risk of progressing to active TB disease 3, 7

Risk of Progressing to Active TB

The risk of progressing to active TB disease after a positive QFT result depends on various factors, including:

• Recent infection with Mycobacterium tuberculosis 7
• Exposure time to the bacteria 7
• Presence of risk factors, such as immunosuppression or recent travel to a TB-endemic country 4, 6
• Studies have shown that the risk of progression to active TB is higher in individuals with a positive QFT result, especially if they decline preventive treatment 7

Monitoring and Treatment

Monitoring and treatment options for latent TB infection include:

• Isoniazid preventive therapy, which can reduce the risk of progressing to active TB disease 3, 6
• Regular follow-up appointments with a healthcare provider to monitor for signs and symptoms of active TB 6
• The QFT test should not be used to monitor the effect of preventive therapy, as most patients remain QFT positive after treatment 6