What is the significance of TB antigen levels of 0.04, 0.05, and 0.03 IU/mL, a mitogen level of 0.070 IU/mL, and an indeterminate tbgp result in the context of tuberculosis testing?

From the Guidelines

The indeterminate QuantiFERON-TB Gold test result indicates that further evaluation is necessary to determine the presence of latent tuberculosis infection, and I recommend discussing these results with your healthcare provider at Valley Medical Group to decide on the best course of action, which may include repeating the test, performing alternative TB testing, or conducting additional evaluations like a chest X-ray, as suggested by the guidelines for using interferon gamma release assays to detect Mycobacterium tuberculosis infection 1. The indeterminate result is likely due to the low mitogen response (0.070 IU/mL), which suggests your immune system may not have responded adequately to the test. According to the guidelines for using the QuantiFERON-TB Gold test for detecting Mycobacterium tuberculosis infection 1, an indeterminate result does not provide useful information regarding the likelihood of M. tuberculosis infection, and the optimal follow-up has not been determined. Some possible next steps include:

• Repeating the QuantiFERON-TB Gold test with a newly obtained blood specimen
• Administering a tuberculin skin test (TST)
• Conducting additional evaluations like a chest X-ray, especially if you have symptoms or risk factors for TB It is essential to note that indeterminate results do not mean you have TB; they simply mean the test could not provide a clear answer, which can happen due to immunosuppression, improper sample handling, or technical issues with the test, as mentioned in the guidelines for using interferon gamma release assays to detect Mycobacterium tuberculosis infection 1. Follow-up is crucial to properly assess your TB status, particularly if you have TB risk factors or are being screened before starting immunosuppressive therapy, and the healthcare provider should consider the epidemiologic and medical history as well as other clinical information when making decisions about medical or public health management 1.

From the Research

Interpretation of Test Results

• The provided test results show the following values:
  • nil: 0.04 IU/mL
  • TB1 antigen: 0.05 IU/mL
  • TB2 antigen: 0.03 IU/mL
  • mitogen: 0.070 IU/mL
  • tbgp: INDETERMINATE negative
• These results are from the Valley Medical Group, dated 04-18-2025.

Treatment of Tuberculosis

• According to 2, the standard treatment for latent tuberculosis is nine months of isoniazid taken daily, or twice weekly under direct observation by a healthcare worker.
• For active or suspected tuberculosis, initial therapy should include isoniazid, rifampin, pyrazinamide, and ethambutol until susceptibility is known 2.
• The continuation phase of treatment for patients with drug-susceptible pulmonary tuberculosis should be a combination of isoniazid and either rifampin or rifapentine, taken for 4 or 7 months depending on risk factors 2.

Treatment Outcomes and Regimens

• A study published in 3 found that a 6-month regimen of isoniazid, rifampin, pyrazinamide, and ethambutol produced successful outcomes in patients with isoniazid-resistant tuberculosis.
• Another study 4 discussed the use of rifamycin-based regimens for latent TB infection, which have been shown to be safe and effective in preventing progression to TB disease.
• The treatment of multidrug-resistant tuberculosis should be individualized and based on susceptibility studies, with consultation from an expert in tuberculosis recommended 5.

Pharmacokinetics of Tuberculosis Drugs

• A study published in 6 evaluated the pharmacokinetics of rifampin, isoniazid, pyrazinamide, and ethambutol in a cohort of tuberculosis patients and found that several factors, including HIV infection, formulation factors, and patient characteristics, can affect drug concentrations.