+ TB Skin Testing
- What is TB or Tuberculosis?
- Who needs to be tested?
- How is the test performed?
- What does a negative or positive TB skin test mean?
- What does a positive TB skin test result mean?
- What is the difference between a TB infection and TB disease?
- Is there a fee?
TB is a highly contagious disease which is caused by the spread of active TB germs known as Tubercle bacilli. Only people who are sick with pulmonary TB are infectious. The disease primarily affects the respiratory system and is transmitted like the common cold by coughing, sneezing and spitting of active TB germs.
A TB or tuberculin skin test can determine if a person has ever been "infected" by TB germs.
Testing for TB is done for several reasons:
1. The test should be performed on people who have had close daily contact with someone who has active TB disease. This could be a co-worker, friend or family member.
2. People who have symptoms of TB, such as:
- A persistent cough
- Fever
- Weight loss
- Night sweats
- Fatigue
- Loss of appetite
3. People who have to be tested for school or a job.
A small amount of a harmless substance called PPD tuberculin is placed just under the top layer of the skin of a person's arm with a very small needle and syringe. The skin test reaction must be read by a health care professional two to three days later (48 - 72 hrs.). The skin test reaction is measured and the results are noted. The test is determined to be positive or negative depending on the measurement of the skin reaction.
What does a negative TB skin test mean?
A negative result in most cases means that the person has not been infected with TB germs. In some cases, where a person has been exposed to someone with active TB, this can mean that the person was tested too soon after breathing in the germs. It may take many weeks after being infected for the body to react to the skin test. To ensure that the result is accurate, the test will have to be repeated again after 3 months.
What does a positive TB skin test result mean?
A positive result means that TB germs are present in the body. Although the person is infected by TB germs, it does not necessarily mean that he/she has TB disease. The infected person will be sent for a chest x-ray to determine if any damage has been done to the lungs. If the x-ray is normal, the TB germs are most likely inactive and TB disease is not present. TB medication may be given to prevent the development of active TB disease in the future.
What is the difference between a TB infection and TB disease?
TB Infection (Inactive TB)
In most cases, after the TB germs enter the body, the body's immune system recognizes the invasion of the TB and initiates an immune response. The cells of the lungs begin to multiply and form a wall around the invading germs. This prevents the TB from spreading, the bacteria no longer affect the body and therefore it is deemed as being in an "inactive state."
TB Disease (Active TB)
The TB germs can stay alive within the walls of the lungs for several years, and may become active if the body's immune system weakens, due to aging, serious illness, drug or alcohol abuse or HIV infection. When the TB germs become active, the result is TB disease.
Resources
A fee of $30 (first visit) and $15 (reading) will be charged if the TB testing is required for volunteering or for working within a hospital setting.