CDC Guidelines for Use of QuantiFERON®-TB Gold Test Philip LoBue, MD Centers for Disease Control and Prevention Division of Tuberculosis Elimination

Outline Where to find 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

Where Can You Find the Guidelines? Print: Guidelines for Using the 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

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 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 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 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 QFT-G

An indeterminate QFT-G result does not provide useful information regarding the likelihood of M. tuberculosis infection Optimal follow up of persons with 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 In situations with serial testing for M. tuberculosis infection (e.g., health-care workers), initial two-step testing (necessary for TST) is not necessary for QFT-G In contrast to TST, there is no boosting with QFT-G

Future Research Needs

More data on performance of QFT-G in special populations (e. g More data on performance of QFT-G in special populations (e.g., children, immunocompromised) Longitudinal studies Subsequent TB disease incidence after LTBI has been either diagnosed or excluded with QFT-G Length of time after infection for QFT-G test result to become positive Changes in QFT-G results with therapy for TB disease and LTBI Economic evaluation and decision analysis comparing QFT-G with TST

Questions?