Tuberculosis (TB) Testing FAQ

This is actually two skin tests that are ideally separated by 1-3 weeks, but can be separated by up to twelve months.

2 Step testing is useful for the initial skin testing of adults who are going to be retested annually, such as health care workers or nursing home residents. This two-step approach provides a more accurate baseline of TB infection status. This more accurate baseline reduces the likelihood that a subsequent positive TB skin test will be misinterpreted as a recent (new) infection.

A student who has a TB skin test that is evaluated as 'positive', should contact Dr. Smachlo for further evaluation.

For anyone who has had a severe reaction to a TB skin test, make an appointment to see Dr. Smachlo, otherwise, start with a TB skin test.

Yes. You should postpone your TB skin test if you have had a live vaccine (MMR, oral polio, oral typhoid, varicella, yellow fever) in the past 4-6 weeks. Do not have a TB skin test if you had a positive documented test in the past.

A negative X-RAY indicates lack of TB lung disease. It is does not indicate whether a person is infected with TB or not. Thus, infected persons who are at risk of developing disease are not identified. Persons infected with TB should consider therapy for their infection.

Most people with a BCG vaccine at birth will not have a resultant positive PPD as an adult, but a few will. If you have a positive result, a blood test, which is not affected by the BCG vaccine, can be arranged by contacting Dr. Smachlo.

These are Interferon-Gamma Release Assays (IGRAs). The 2 FDA- approved are the T-SPOT.TB (T-SPOT) and QuantiFERON-TB Gold- In-Tube (QFT-GIT, or Quantiferon). They, like skin tests, are used to diagnose TB infection, and like skin tests, they cannot differentiate between infection and disease.

Both tests have about the same sensitivity, 80-90%. Unlike the skin test, the blood tests will not give a false-positive in a person who has had a BCG vaccine, which sometimes occurs, especially in persons who received a BCG after the first year of life. Also, they are not affected by some non-Tuberculous Mycobacterium that exist in some environments.

A person who has a positive TB skin test.

In the United States, most insurance companies will not cover the cost of a TB blood test unless there is a history of a past positive TB skin test.

The Case Student Medical Plan requires a history of a past positive TB skin test before it will cover the cost of a TB blood test.

If you are in a health related program that requires annual TB testing, and you start with a TB blood test, but cannot continue with TB blood testing, you will need a '2 Step' TB skin test a year later.

TB skin testing is provided at University Health Service at no charge for currently enrolled students.

TB blood testing cost varies depending on where it is done.

If you are in a health related program that requires annual TB testing, and your TB blood test result is negative, you should have the TB blood test every 12 months to assure you have not been exposed to TB through your clinical activities.

A positive TB blood test result may indicate a tuberculosis infection. A student with a positive TB blood test should contact Dr. Smachlo, at the University Health Service, for clinical evaluation and treatment advice.