Download Follow up of Indeterminate QFT-G An indeterminate QFT

CDC Guidelines for Use of
QuantiFERON®-TB Gold Test
Philip LoBue, MD
Centers for Disease Control and Prevention
Division of Tuberculosis Elimination
Outline
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Background and purpose
Where to find guidelines
Methods for developing guidelines
Recommendations for QFT-G use
Guidance for follow up of
– Positive test result
– Negative test result
– Indeterminate test result
Special situations
– Contact investigation
– Serial testing (e.g., occupational)
Future research needs
Future guidelines
Background and Purpose
• QFT-G received final approval from FDA as
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an aid for diagnosing M. tuberculosis
infection in May 2005
CDC statement (published December 2005)
meant to provide interim guidance for use
and interpretation of QFT-G
Where Can You Find the Guidelines?
• Print: Guidelines for Using the
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QuantiFERON®-TB Gold Test for Detecting
Mycobacterium tuberculosis Infection, United
States, MMWR, December 16, 2005 / Vol. 54 /
No. RR-15, pp. 49-54.
Internet:
http://www.cdc.gov/nchstp/tb/pubs/mmwrhtml
/maj_guide.htm
Methods for Developing Guidelines
• Panel of expert consultants convened July
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2005
Reviewed published and unpublished data
In developing guidelines, CDC reviewed
scientific evidence independently and
considered opinion of consultants
Recommendations for Use of QFT-G
QFT-G can be used in all
circumstances in which
the TST is used, including
• Contact investigations
• Evaluation of recent immigrants who have
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had BCG vaccination
TB screening of health-care workers and
others undergoing serial evaluation for M.
tuberculosis infection
QFT-G usually can be used in place of
(and usually not in addition to) the TST
Follow up of Positive QFT-G
A positive QFT-G should prompt the same
health and medical interventions as a
positive TST result
• No reason exists to follow a positive QFT-G
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with a TST
Persons with a positive QFT-G result should
be evaluated for TB disease before LTBI is
diagnosed
After TB has been excluded, treatment of
LTBI should be considered
Follow up of Negative QFT-G
The majority of healthy adults who have
negative QFT-G results are unlikely to
have M. tuberculosis infection and do not
require further evaluation
Cautions and Limitations
• As with a negative TST result, negative QFT-G results
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should not be used alone to exclude M. tuberculosis
infection in persons with symptoms or signs suggestive
of TB disease
The performance of QFT-G has not been determined in
persons who, because of impaired immune function
(e.g., HIV infection), are at increased risk for M.
tuberculosis infection progressing to TB disease
As with a negative TST result, negative QFT-G results
alone might not be sufficient to exclude M. tuberculosis
infection in immunocompromised persons
Limited published data document the performance of
QFT-G in children aged <17 years
Follow up of Indeterminate QFTG
An indeterminate QFT-G result does not
provide useful information regarding the
likelihood of M. tuberculosis infection
• Optimal follow up of persons with
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indeterminate QFT-G results has not been
determined
Options are to repeat QFT-G with a new
blood sample, administer a TST, or do neither
Decision should be based on pre-test
likelihood of M. tuberculosis infection
Contact Investigations
For persons with recent contact to an
infectious TB patient, negative QFT-G
results should be confirmed with a repeat
test 8-10 weeks after exposure (end of
window period) as is recommended for a
negative TST
When “window prophylaxis” has been started
for high-risk contacts exposed to an infectious
TB patient, a negative QFT-G result at the end of
the window period should be interpreted in light
of all other clinical and epidemiologic data
• A full course of LTBI treatment should be
considered even with a negative result when the
rate of M. tuberculosis transmission to other
contacts is high or when a false-negative result is
suspected because of an immunocompromising
medical condition
Serial Testing
(e.g., Healthcare Workers)
In situations with serial testing for
M. tuberculosis infection (e.g.,
health-care workers), initial twostep testing (necessary for TST) is
not necessary for QFT-G
• In contrast to TST, there is no boosting with
QFT-G
Future Research Needs
• Performance of QFT-G in young children
• Performance of QFT-G in persons with impaired
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immunity (e.g., HIV)
Performance and practicality of QFT-G in
substantial numbers of persons who undergo
periodic screening
Determination of subsequent incidence of TB
disease after LTBI has been either diagnosed or
excluded with QFT-G
Length of time between exposure, establishment of
infection, and emergence of a positive QFT-G test
result
• Economic evaluation and decision analysis
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comparing QFT-G with TST
Changes in QFT-G results with therapy for
TB disease and LTBI
Ability of QFT-G to detect re-infection after
treatment for LTBI and TB disease
Performance of QFT-G in targeted testing
programs (e.g., recent immigrants from highincidence countries)
Future Guidelines
• Current guidelines will be modified or new
guidelines developed as
– Additional studies on QFT-G are published
– New versions of QFT and other interferongamma release assays become available