Assessing the Accuracy of Tuberculin Skin Test in Children

What is the accuracy of the tuberculin skin test?

A child was born abroad and has not received the BCG vaccine.
They are now in the first grade of elementary school.
Recently, the school conducted a tuberculin skin test, which resulted in a positive reaction.
No family members are infected, and both the parents and child have normal chest X-rays.
The child's growth is normal and tall for their age.
The child has a history of allergies and often experiences nasal congestion.
At the time of the tuberculin test, the child had post-nasal drip and mild cold symptoms.

Doctor, is the test result accurate under these circumstances? Could there be a false positive? What methods can be used to confirm whether the child is truly infected? Thank you!

Kaisi, 30~39 year old female. Ask Date: 2005/05/06

Dr. Liang Hongjian reply Pediatrics

Thank you for your letter, Miss Casey.
Generally, a positive tuberculin skin test indicates the following: 1.
For HIV-positive patients with significant fibrosis on their chest X-ray, a test result greater than 5 mm, and a history of exposure to an active TB patient, they may be considered as having TB.
2.
For individuals who have been in contact with TB patients, or have returned from endemic areas, or high-incidence regions, a test result greater than 10 mm is significant, especially in patients under 10 years old.
3.
A result greater than 15 mm is less likely to indicate exposure to TB.

As for the circumstances that warrant treatment: 1.
Recurrent fibrotic changes.
2.
HIV-positive status.
3.
Contact with recently diagnosed TB patients.
4.
Contact with TB-reactive individuals who are currently undergoing treatment, or those with substance abuse issues, or those receiving chemotherapy, or long-term steroid therapy.
5.
Patients with a risk factor of less than 35% in high-risk areas.

Given your current situation, the likelihood of TB is low, but for precautionary measures, you may consider visiting a nearby hospital or medical center for further evaluation.
As for the possibility of a false positive, that is difficult to determine.
Wishing you good health!

Reply Date: 2005/05/06

More Info

The tuberculin skin test (TST), also known as the Mantoux test, is a widely used method for screening tuberculosis (TB) infection, particularly in children. However, interpreting the results can be complex, especially in the context of a child who has not received the BCG vaccine, has a normal chest X-ray, and presents with mild respiratory symptoms.
In your case, the child tested positive for the TST, which indicates that there has been some exposure to the tuberculosis bacteria. However, several factors can influence the accuracy of this test, leading to potential false-positive results.
1. False Positives: The TST can yield false-positive results due to various reasons, including prior exposure to non-tuberculous mycobacteria, recent vaccinations (though this is less likely in your case since the child has not received the BCG vaccine), or even certain medical conditions that can cause immune responses. Given that your child has allergies and was experiencing mild cold symptoms at the time of testing, these factors could potentially affect the test's accuracy.
2. Interpretation of Results: The size of the induration (swelling) at the test site is crucial for interpretation. In children, a reaction of 10 mm or more is generally considered positive, especially if there are risk factors for TB exposure. However, the context of the child's health, exposure history, and other diagnostic results must be taken into account. Since your child has a normal chest X-ray and no known exposure to active TB cases, the likelihood of a true infection may be lower.

3. Confirmatory Testing: To ascertain whether the child has a true TB infection, further testing is often recommended. This may include:
- Chest X-ray: As already done, to check for any signs of active TB disease.

- Interferon-gamma release assays (IGRAs): These blood tests can provide additional information regarding TB infection and are not affected by prior BCG vaccination.

- Clinical evaluation: A thorough assessment by a healthcare provider, considering the child's symptoms, history, and family background.

4. Management: If there is still uncertainty regarding the child's TB status, it may be prudent to consult a pediatric infectious disease specialist. They can provide guidance on whether preventive treatment is necessary, especially considering the child's overall health and the absence of active disease in the family.

In conclusion, while a positive TST result in your child raises concerns about TB infection, the absence of symptoms, normal chest X-ray, and lack of known exposure to active TB significantly reduce the likelihood of a true infection. However, further evaluation through additional testing and clinical assessment is essential to confirm the diagnosis and determine the appropriate management plan. Always consult with a healthcare professional for personalized advice and treatment options.

Similar Q&A

Understanding Tuberculin Skin Tests in Young Children: What Parents Should Know

Doctor, my child is two years and two months old and has been in contact with a person who has open pulmonary tuberculosis for 48 hours. However, this individual has a very low bacterial load and is completely asymptomatic. My child had a chest X-ray that came back normal, and th...

Dr. Ma Yiqun reply Pediatrics
Definition of a positive tuberculin skin test: 1. >= 10mm: for children over 6 years old or those with risk factors for tuberculosis. 2. >= 15mm: for children 6 years old or younger without risk factors for tuberculosis. Although your child is under 6 years old and has rece...

Understanding Tuberculosis Testing: X-rays, Interferon, and More

Currently, the tests for tuberculosis (TB) include chest X-rays, tuberculin skin tests (TST), and other more accurate out-of-pocket tests. One such test is the Interferon Gamma Release Assay (IGRA), which is a blood test that detects the immune response to TB bacteria. Your chi...

Dr. Jian Shuntian reply Pulmonology
Hello, no test is 100% accurate, so it is necessary to consider all examinations to make a judgment on whether preventive medication is needed. The physician will explain the benefits and risks, but the final decision rests with the parents. Preventive treatment will only be admi...

Assessing Tuberculosis Transmission Risk in Young Children

If an adult's sputum smear test is negative but a bacterial culture shows a very low quantity of bacteria, and my two-year-old child has been in close contact with this adult for 48 hours, what is the likelihood of transmission? The child has had a normal chest X-ray, and we...

Dr. Xiao Kaiwen reply Pediatrics
Tuberculosis (TB) is not as easily transmitted as one might think. The likelihood of transmission depends on several factors, including the bacterial load of the infected individual, whether they have open pulmonary tuberculosis, the distance between individuals, personal immunit...

Understanding Skin Test Reactions for Tuberculosis: What to Expect

Hello, doctor. I had a skin test injection on Tuesday, and after 48 hours, the result was negative with only a slight erythema but no swelling. However, after the examination (which involved palpation) at 72 hours, it has become slightly red and swollen, approximately 10mm. This ...

Dr. Yang Wenda reply Pulmonology
1. Each individual's constitution is different, and the reaction time to a coin-sized stimulus can vary significantly. If the diameter of the reaction reaches approximately 10mm within 72 hours, this value should be used as a reference for assessment. 2. Theoretically, there...