Tuberculosis Skin Test Results and Follow-Up Options

Q: Tuberculosis Skin Test Results and Follow-Up Options

Hello： 1. Blood tests can be performed to measure interferon-gamma release assays (IGRA) for decision-making. 2. The chance of misdiagnosis is low; it is not uncommon to have a negative result on the first test and a positive result on the second. 3. Prior vac

Subcutaneous Tuberculin Test

On September 1st of this year, the first tuberculin skin test was negative, with normal blood tests and chest X-ray results.
On November 3rd, the second skin test showed a result of 13mm, indicating a positive reaction.
The health center issued a referral to the pulmonology department, where a chest X-ray was also normal, and the health center requested medication.

1.
Given the close timing of the two skin tests, is this correct? Could there be a misinterpretation of the results?
2.
If I do not wish to take medication, are there any testing methods available to confirm whether there is an infection?
3.
I am currently fifty years old and received the BCG vaccine in elementary school; could this affect the results of the skin test?
4.
If I choose not to take medication, what is the shortest time frame in which I can have another chest X-ray to confirm whether there is an infection?

Sid, 50~59 year old female. Ask Date: 2020/11/19

Dr. Jian Shuntian reply Pulmonology

Hello: 1.
Blood tests can be performed to measure interferon-gamma release assays (IGRA) for decision-making.
2.
The chance of misdiagnosis is low; it is not uncommon to have a negative result on the first test and a positive result on the second.
3.
Prior vaccination with BCG may have an impact, and the longer the interval since vaccination, the lesser the effect.
4.
If you prefer not to take medication, you can have a chest X-ray every six months to a year to monitor for disease or infection.

Reply Date: 2020/11/19

More Info

Understanding tuberculosis (TB) skin test results and the appropriate follow-up options is crucial for effective management and prevention of the disease. Let's break down your questions regarding the recent skin test results and the implications for your health.

1. Timing of Skin Tests: The first skin test being negative and the second test showing a positive result of 13mm within a short time frame (approximately two months) can be concerning. It is possible for a person to develop a positive reaction to the TB skin test (also known as the Mantoux test) if they were recently infected with the bacteria that cause TB. However, false positives can occur, especially in individuals who have received the Bacillus Calmette-Guérin (BCG) vaccine, which is commonly administered in childhood in many countries to provide some level of immunity against TB. The timing of the tests is not inherently incorrect, but it does warrant further investigation to rule out any misinterpretation or other factors influencing the results.

2. Alternative Testing Methods: If you are hesitant about starting treatment, there are alternative tests available to confirm TB infection. The Interferon Gamma Release Assays (IGRAs) are blood tests that can help determine if you have been infected with TB bacteria. These tests are not affected by prior BCG vaccination and can provide a more definitive answer regarding your TB status. Discussing these options with your healthcare provider can help you make an informed decision.

3. Impact of BCG Vaccination: As mentioned, having received the BCG vaccine in childhood can affect the results of the TB skin test. While the vaccine can provide some protection against severe forms of TB, it can also lead to false-positive results on the skin test. This is why healthcare providers often consider a person's vaccination history when interpreting skin test results. However, the IGRA tests are not influenced by prior BCG vaccination, making them a reliable option for assessing TB infection status in vaccinated individuals.

4. Follow-Up Chest X-Ray: If you choose not to start medication immediately, it is advisable to have a follow-up chest X-ray to monitor for any signs of active TB infection. The timing for this follow-up can vary, but generally, a repeat chest X-ray can be performed within a few months after the positive skin test. Your healthcare provider will consider your overall health, risk factors, and any symptoms you may have when determining the appropriate timing for this follow-up.

In conclusion, it is essential to have open communication with your healthcare provider regarding your concerns about TB testing and treatment. They can provide personalized advice based on your medical history, the results of your tests, and your preferences. Early detection and treatment of TB are critical in preventing the spread of the disease and ensuring your health and safety. If you have any further questions or concerns, do not hesitate to reach out to your healthcare provider for clarification and guidance.

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