From the Guidelines
For a patient with a positive PPD test but negative Quantiferon test, treatment for latent tuberculosis infection (LTBI) is generally not recommended unless the patient has specific risk factors. In this discordant result scenario, the negative Quantiferon test is typically considered more reliable as it has higher specificity and is less affected by prior BCG vaccination 1. However, treatment should be considered if the patient has significant risk factors such as recent close contact with active TB cases, immunosuppression, HIV infection, or radiographic evidence of prior TB.
When treatment is deemed necessary, the preferred regimens are:
- 3 months of once-weekly isoniazid plus rifapentine
- 4 months of daily rifampin
- 3 months of daily isoniazid plus rifampin, as these short-course rifamycin-based treatment regimens are preferred over longer-course isoniazid monotherapy for treatment of LTBI 1. The decision to treat should be individualized based on the patient's complete clinical picture, weighing the risk of TB reactivation against potential medication side effects. Patients should be monitored for hepatotoxicity during treatment with baseline and periodic liver function tests.
Key considerations in the treatment decision include the patient's overall health status, the presence of any underlying medical conditions, and the potential for drug interactions. It is essential to carefully evaluate the patient's risk factors and medical history to determine the most appropriate course of treatment. According to the guidelines from the National Tuberculosis Controllers Association and CDC, published in 2020 1, these updated guidelines can be used by clinicians to adapt them to fit individual clinical circumstances.
From the Research
Diagnosis and Treatment of Latent Tuberculosis Infection
- The patient has a positive Purified Protein Derivative (PPD) test but a negative Quantiferon test for latent tuberculosis infection (LTBI) 2.
- The PPD test has low specificity due to cross-reactivity with Bacillus Calmette-Guerin (BCG) vaccination or non-tuberculous mycobacterium (NTM) infections 3.
- The Quantiferon test, on the other hand, uses specific antigens (ESAT-6 and CFP-10) to stimulate whole blood and diagnose LTBI, reducing cross-reactivity with BCG vaccination or NTM infections 3.
Treatment Options for LTBI
- The recommended treatment for LTBI is isoniazid daily for 9 months, but this regimen has been associated with hepatotoxicity and low treatment completion rates 4.
- Alternative treatment regimens, such as 12 weekly doses of isoniazid and rifapentine (INH-RPT), have shown high completion rates and good tolerability 4, 5.
- However, the choice of treatment regimen should be individualized based on patient factors, such as liver function and potential drug interactions.
Clinical Considerations
- Patients with a positive PPD test and a negative Quantiferon test may still be at risk for LTBI, particularly if they have a history of BCG vaccination or exposure to TB 2, 6.
- Clinical judgment and additional testing, such as chest radiography and clinical assessment, may be necessary to determine the need for treatment 6.
- The agreement between LTBI diagnosis using standard methods and IGRA by QFT was poor in kidney transplant recipients, highlighting the need for careful evaluation and individualized decision-making 6.