Information on Two-Step TB Skin Test - College of Pharmacy

<strong>Information</strong> on Two-Step TB Skin Test
The two-step test is NOT the usual PPD skin test in which you receive an injection of PPD
and the test area is observed one time at specific time frame.
The two-step PPD test is used to detect individuals with past TB infection who now have
diminished skin test reactivity. This procedure reduces the likelihood that a boosted
reaction is later interpreted as a new infection.
The reason for the 2 stage PPD test appears to be the "booster phenomenon.” It occurs
in some people who were infected with TB in the past because the body loses its ability
to react to the tuberculin solution. Thus, when these people are tested many years after
the initial infection they may have a negative reaction. However, if they are tested a
second time within up to one year of the first test, they may have a positive reaction. This
positive reaction is due to a "boosted" ability to react to the tuberculin solution. To avoid
misinterpretation between a boosted response and a new infection, many facilities
employ the 2-step testing procedure. In this procedure a person is given a baseline PPD
test. If the test is negative, a second test is administered one to three weeks later. If the
second test is negative, the person is considered uninfected. If the second test is
positive, then the person is considered to have a "boosted" reaction to an infection that
occurred a long time ago.
Beyond that, secondary testing is useful to help offset potential false negative testing
results. The sensitivity of tuberculin testing in patients presenting with newly diagnosed
pulmonary tuberculosis can be as low as 80% in immuno-suppressed or otherwise
unhealthy or compromised patients. The 20 percent false-negative rate is due to a
combination of immuno-suppression of delayed hypersensitivity from cytokines as well as
factors relating to acute illness and/or poor nutrition. Even once these patients have
returned to normal health and nutrition status, such as those of the general population,
the sensitivity of tuberculin testing is still only approximately 95 percent. This one-in-twenty
false negative rate could certainly warrant the use of secondary testing, especially for
those subjects in a healthcare setting.
The second step must be completed within 12 months of the first step. However, the
College of Pharmacy would prefer that it be done within 72 hours.
The number of visits required may be reduced to three by using the following procedure.
However, if the health care agency does not want to follow this procedure, you must
follow their directions. At the UF Student Health Care Center, their protocol requires that
students come back at 48 hours of the first PPD test for a read. Thus, this requires four
visits rather than three visits as described below.
The Three Visit Approach
Visit 1, Day 1
The first skin test is applied and the individual returns in 7 days for the test to be read. If
the first test is positive, it indicates that the individual is infected with TB. A chest X-ray
and evaluation is necessary. If the individual is asymptomatic and the chest X-ray
indicates no active disease, the individual can enter patient care areas.
Visit 2, Day 7
A second skin test is applied on individuals whose first test was negative at 7 days.
Visit 3, Day 9 or 10

The second test is read. A positive test 2nd test indicates TB infection in the distant past.
The individual is referred for a chest X-ray and evaluation by a physician. An
asymptomatic individual, whose chest X-ray indicates no active disease may enter
patient care areas.
The majority of significant PPD skin test reactions will remain "positive" for 7 days after
application. Those that have diminished or disappeared by day 7 will be boosted back
to positive by the 2nd skin test. Reducing the number of visits from 4 to 3 will not reduce
the sensitivity of the two-step test.
The Four Visit Approach
Visit 1, Day 1
The PPD antigen is applied under the skin.
Visit 2, Day 3
The PPD test is read. If the first test is positive, it indicates that the individual is infected
with TB. A chest X-ray and evaluation is necessary. If the individual is asymptomatic and
the chest X-ray indicates no active disease, the individual can enter patient care areas.
Visit 3, Day 7
A second PPD skin test is applied to those individual in whom the PPD skin test is negative.
Visit 4, Day 9
The second test is read. A positive test 2nd test indicates TB infection in the distant past.
The individual is referred for a chest X-ray and evaluation by a physician. An
asymptomatic individual whose chest X-ray indicates no active disease may enter
patient care areas.
For those individuals who were vaccinated against TB with BCG vaccine, you still can be
tested with PPD after a 3-5 year period post the BCG vaccination. Positive PPD tests at
this point could indicate TB infection. Thus, a chest x-ray is necessary.
When a two-step PPD is indicated during the curriculum
(http://www.cop.ufl.edu/studaff/prac1.pdf) and a student has shown prior evidence of
either positive PPD or BCG vaccination*, an updated health statement by a physician
should be provided. It is the physician’s determination whether or not an additional
chest x-ray is warranted. Please provide a physician’s interpretation of a recent chest xray
(within a month of a deadline for this information) and/or a physician’s statement
that there is no clinical evidence of active TB infection and that you are permitted to
enter patient care environments. The physician’s statements about the chest x-ray
interpretation and/or clinical assessment of your status with regard to active TB should be
on the physician’s letterhead with the student’s full name and UFID.
*BCG vaccination can result in positive PPD tests for a period of approximately 3-5 years.
After this time, PPD skin tests can be administered. A positive PPD after this time frame
could still indicate possible reaction to the antigens in BCG vaccine or exposure to the
tuberculosis organism. A follow-up chest x-ray and clinical assessment as determined by
a physician may be necessary for a positive PPD under this circumstance.
H/Group/Student Affairs/Background Checks and Data Collection/TB/<strong>Information</strong> on Two Step PPD.doc
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