VITAL INFO - Alternative TB TEST! (blood test)
ASK FOR THIS TEST instead of getting the PPD or other TB test! (PPD has TB
in it and can be just as dangerous as a vaccine - I know several children
who regressed back into autism after receiving a TB test)
From one of my students.....
"They just draw a tube of blood, which I have no problem with. No ppd. I've
got an email in to my Kaiser dr. asking for this. If they don't do it or
the cost is prohibitive,
the SF health dept. does it for $13"
* The QFT-G should be used in all settings in which the TST is
currently used, including contact investigations, evaluation of recent
immigrants with BCG vaccination, and TB screening of healthcare providers.
* Advantages of the QFT-G vs the TST include specificity for
individuals with a history of BCG vaccine and convenience of
administration. Data on the sensitivity of the QFT-G for children,
immunocompromised individuals, and its ability to predict disease
progression are needed.
Tuberculosis Testing - What is the QuantiFERON-TB Test?
From Stacey Lloyd,Your Guide to Lung Diseases.
Tuberculosis Testing Choices
In 2001, the Food and Drug Administration (FDA) approved the tuberculosis
test called QuantiFERON-TB (QFT). This tuberculosis test measures the
release of interferon-gamma (IFN-g) in whole blood in response to
stimulation of the purified protein derivative from M. tuberculosis. In
laymen's terms, the QFT tuberculosis test measures a person's immune
reactivity to Mycobacterium tuberculosis, the bacterium that causes
How Does the QFT Tuberculosis Test Work?
A blood sample is drawn from the patient. The blood is mixed with antigens
- the protein substances that produce an immune response - and controls.
The antigens include tuberculin, which is purified protein derivative (PPD)
from M. tuberculosis, and avian sensitin, which is purified protein
derivative from My avium complex. Then the blood is incubated for 16 to 24
At the end of the incubation period, the QFT tuberculosis test is read. If
the patient tests positive for tuberculosis, i.e. the patient is infected
with M. tuberculosis, the blood cells would have released a larger
proportion of IFN-g in response to the tuberculin than that released in
response to the avian sensitin or the controls. However, in order to
confirm or exclude a tuberculosis diagnosis, additional testing, such as a
chest x-ray, is required. (Read What You Need to Know Before Getting A
Advantages of QFT Tuberculosis Test
# Only one doctor visit is required
# The test assesses responses to multiple antigens simultaneously
# Eliminates the concern of the booster phenomenon as seen with the PPD
tuberculosis skin test
# Reduced risk of testing interpretation errors and bias
Disadvantages of QFT Tuberculosis Test
# Time limit (12 hours) for testing of the drawn blood
# Limited knowledge and experience with QFT tuberculosis test
# The QFT's ability to predict the progression of tuberculosis infection to
tuberculosis disease has not been evaluated
# Additional testing required to confirm or exclude tuberculosis diagnosis
Return to Fact Sheets Main Menu
QuantiFERON®-TB Gold Test
What is it?
The QuantiFERON®-TB Gold test (QFT-G) is a whole-blood test for use as an
aid in diagnosing Mycobacterium tuberculosis infection, including latent
tuberculosis infection (LTBI) and tuberculosis (TB) disease. This test was
approved by the U.S. Food and Drug Administration (FDA) in 2005.
How does it work?
Blood samples are mixed with antigens (substances that can produce an
immune response) and controls. For QFT-G, the antigens include mixtures of
synthetic peptides representing two M. tuberculosis proteins, ESAT-6 and
CFP-10. After incubation of the blood with antigens for 16 to 24 hours, the
amount of interferon-gamma (IFN-gamma) is measured.
If the patient is infected with M. tuberculosis, their white blood cells
will release IFN-gamma in response to contact with the TB antigens. The
QFT-G results are based on the amount of IFN-gamma that is released in
response to the antigens.
Clinical evaluation and additional tests (such as a chest radiograph,
sputum smear, and culture) are needed to confirm the diagnosis of LTBI or
What are the advantages?
* Requires a single patient visit to draw a blood sample.
* Results can be available within 24 hours.
* Does not boost responses measured by subsequent tests, which can
happen with tuberculin skin tests (TST).
* Is not subject to reader bias that can occur with TST.
* Is not affected by prior BCG (bacille Calmette-Guérin) vaccination.
What are the disadvantages and limitations?
* Blood samples must be processed within 12 hours after collection
while white blood cells are still viable.
* There are limited data on the use of QFT-G in children younger than
17 years of age, among persons recently exposed to M. tuberculosis, and in
immunocompromised persons (e.g., impaired immune function caused by HIV
infection or acquired immunodeficiency syndrome [AIDS], current treatment
with immunosuppressive drugs, selected hematological disorders, specific
malignancies, diabetes, silicosis, and chronic renal failure).
* Errors in collecting or transporting blood specimens or in running
and interpreting the assay can decrease the accuracy of QFT-G.
* Limited data on the use of QFT-G to determine who is at risk for
developing TB disease.
When should you use the test?
QFT-G can be used in all circumstances in which the tuberculin skin test
(TST) is currently used, including contact investigations, evaluation of
recent immigrants who have had BCG vaccination, and TB screening of health
care workers and others undergoing serial evaluation for M. tuberculosis.
However, caution should be used when testing certain populations because of
limited data in the use of QFT-G.
Before the QFT-G is conducted, arrangements should be made with a qualified
laboratory and courier service, if needed, to ensure prompt and proper
processing of blood.
What are the steps in administering the test?
* Confirm arrangements for testing in a qualified laboratory and
arrange for delivery of the blood sample in time for the laboratory to
initiate testing within 12 hours of blood collection.
* Draw a sample of whole blood from patient into a tube with heparin
anti-clotting agent, according to manufacturer's instructions.
* Schedule an appointment for the patient to receive test results and,
if then needed, medical evaluation and possible treatment for TB disease or
How do you interpret test results?
Interpretation of QFT-G results is based on IFN-gamma concentrations in
test samples. Each QFT-G result and its interpretation should be considered
in conjunction with other epidemiological, historical, physical, and
A positive result suggests that M. tuberculosis infection is likely; a
negative result suggests that infection is unlikely; and indeterminate
result suggests QFT-G results cannot be interpreted as a result of low
mitogen response or high background response.
A diagnosis of LTBI requires that TB disease be excluded by medical
evaluation, which should include checking for signs and symptoms suggestive
of TB disease, a chest radiograph, and, when indicated, examination of
sputum or other clinical samples for the presence of M. tuberculosis.
Centers for Disease Control and Prevention. Guidelines for the
investigation of contacts of persons with infectious tuberculosis and
Guidelines for using the QuantiFERON®-TB Gold test for detecting
Mycobacterium tuberculosis infection, United States. MMWR
2005; 54 (No. RR-15).
Centers for Disease Control and Prevention. Guidelines for Preventing the
Transmission of Mycobacterium tuberculosis in Health-Care Settings, 2005.
MMWR 2005; 54 (No.RR-17).
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1: Kekkaku. 2004 Nov;79(11):637-43. Related Articles, Links
[Usefulness of a novel diagnostic method of tuberculosis infection,
QuantiFERON TB-2G, in an outbreak of tuberculosis]
[Article in Japanese]
Harada N, Mori T, Shishido S, Higuchi K, Sekiya Y.
Immunology Division, Research Institute of Tuberculosis, JATA, Tokyo,
OBJECTIVE: The purpose of this study was to evaluate QuantiFERON TB-2G
(QFT), a novel method of detecting tuberculosis infection among contacts of
a tuberculosis patient by determining the whole-blood interferongamma
response to the specific antigens. SUBJECTS AND METHODS: A teacher of a
college who had been coughing for the preceding two months was diagnosed
with smear-positive tuberculosis. About 270 students of the college were
considered to have been exposed to tuberculosis infection, of whom 73 were
in closer contact with the index case because they participated in a
one-week group excursion attended by the teacher. Two of the contact
students developed active tuberculosis shortly thereafter. Tuberculin tests
were conducted to almost all students, and QFT was performed for only those
with tuberculin reactions having erythema diameters of 30 mm or larger.
RESULTS: Tuberculin tests of students, all of whom had been vaccinated with
BCG at least once, revealed that the distribution of the close contact
group was slightly shifted to right (larger side) than those with less
close contacts. The QFT positive rate for close contacts was 45.5%, while
that for less close contacts was only 7.1%, which obviously indicates that
QFT is hardly affected by the tuberculin allergy due to past BCG
vaccination. The distribution of interferon-gamma measurements
(log-transformed) of the close contacts showed typical bimodality, one mode
representing the infected, another the non-infected. This was not clear for
the less close contacts. The correlation of interferon-gamma measurements
(log-transformed) with tuberculin reaction erythema size was weak, if not
non-significant. CONCLUSION: It was concluded that QFT was a useful method
for diagnosing tuberculosis infection and was unaffected by the BCG-caused
tuberculin allergy. In the case of the outbreak mentioned above, QFT
greatly reduced the indication of chemoprophylaxis, from 28% of all the
contacts solely based on tuberculin test to only 7%. Although there remains
some problems to be overcome for QFT to be widely used with high
confidence, this technology will provide a high possibility for wider and
more accurate indication of chemoprophylaxis and will be one of the
essential tools of tuberculosis control of the 21st century in Japan.
PMID: 15729888 [PubMed - indexed for MEDLINE]
CDC Issues Guidelines on Use of QuantiFERON TB Gold Test CME
News Author: Laurie Barclay, MD
Dec. 22, 2005 - The QuantiFERON TB Gold test (QFT-G) essentially can be
used in all cases in which the tuberculosis skin test is currently used,
according to new guidelines released by the US Centers for Disease Control
and Prevention (CDC) and published in the Dec. 16 issue of the Morbidity
and Mortality Weekly Report: Recommendations and Reports. These guidelines
are intended for public health officials, healthcare providers, and
laboratory workers with responsibility for TB control activities in the
"On May 2, 2005, a new in vitro test, QuantiFERON-TB Gold (QFT-G, Cellestis
Limited, Carnegie, Victoria, Australia), received final approval from the
U.S. Food and Drug Administration (FDA) as an aid for diagnosing
Mycobacterium tuberculosis infection," write Gerald H. Mazurek, MD, and
colleagues from the Division of Tuberculosis Elimination, National Center
for HIV, STD, and TB Prevention. "This test detects the release of
interferon-gamma (IFN-?) in fresh heparinized whole blood from sensitized
persons when it is incubated with mixtures of synthetic peptides
representing two proteins present in M. tuberculosis: early secretory
antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10). These
antigens impart greater specificity than is possible with tests using
purified protein derivative [PPD] as the tuberculosis (TB) antigen."
Direct comparisons have shown that the sensitivity of QFT-G was not
statistically different from that of the tuberculin skin test (TST) for
detecting infection in people with untreated culture-confirmed TB.
Currently, the diagnostic value of QFT-G for finding latent TB infection
(LTBI) is being evaluated in certain populations targeted by TB control
programs in the United States. To date, the ability of this test to predict
who will eventually have TB disease is unknown, and years of observational
research in large cohorts would be needed to determine this.
In July 2005, the CDC organized a meeting of experts to review scientific
evidence and clinical experience with QFT-G. This group concluded that
QFT-G may be used in all circumstances in which the TST is now used,
including contact investigations, evaluation of recent immigrants, and
sequential-testing surveillance programs for infection control, such as
those for healthcare workers. The CDC guidelines also list specific
cautions for interpreting negative QFT-G results in selected subgroups
populations and provide interim guidance for use and interpretation of QFT-G.
"Confirming or excluding TB disease and assessing the probability of LTBI
require a combination of epidemiologic, historic, physical, and diagnostic
findings that should be considered when interpreting QFT-G results," the
authors write. "This report is intended to assist public health officials,
clinicians, and laboratorians in their efforts to understand the use of
QFT-G for TB control."
The FDA approved QFT-G as an in vitro laboratory test to assist in the
diagnosis of both TB disease and LTBI, both in clinical and in public
health settings, ideally in concert with the local or regional public
health TB control program. Instructions for the QFT-G assay are in the
package insert, and QFT-G test results can be calculated by using software
provided by the manufacturer. The guidelines also include a table for
interpreting test results. Laboratory reports should include interpretation
of QFT-G test results and indicate the concentration of IFN-? in each
Although some limitations of QFT-G appear to be similar to those of the
TST, they have not been studied extensively to date. In persons with
untreated, culture-confirmed TB, the sensitivity of QFT-G for detecting M.
tuberculosis infection is approximately 80% in published studies, but the
sensitivity in specific subgroups of TB patients, such as young children
and immunocompromised patients, is still unknown. For LTBI, QFT-G
sensitivity might be less than that of the TST, but the lack of a
confirmatory test makes this difficult to evaluate. Estimating the
sensitivity of any indirect test for LTBI by testing patients with TB
disease might be inaccurate because of differences between these
conditions, and the ability of QFT-G to predict risk for LTBI progressing
to TB disease is still undetermined.
Like the TST, QFT-G cannot distinguish infection associated with TB disease
from LTBI. For definitive diagnosis of LTBI, TB disease must be ruled out
by medical evaluation, which should include ascertaining history of
suggestive symptoms and signs, chest x-ray, and examination of sputum or
other clinical samples for M. tuberculosis when indicated. As for other
diagnostic tests, the prevalence of M. tuberculosis infection in the
population being tested affects the predictive value of QFT-G results.
"Each QFT-G result and its interpretation should be considered in
conjunction with other epidemiologic, historic, physical, and diagnostic
findings," the guidelines note. "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 presence of
symptoms or signs suggestive of TB disease increases the likelihood that M.
tuberculosis infection is present, and these circumstances decrease the
predictive value of a negative QFT-G or TST result."
Symptomatic individuals should have a medical evaluation including history
and physical examination, chest x-ray, bacteriologic studies, serology for
HIV, and other tests as indicated.
The sensitivity and rate of indeterminate results using QFT-G has not been
determined in immunocompromised persons with HIV infection, AIDS, current
treatment with immunosuppressive drugs, selected hematologic disorders, and
certain malignancies. These conditions or treatments are known or suspected
to decrease responsiveness to the TST, and they might also decrease
production of IFN-? in the QFT-G assay. As with a negative TST result,
negative QFT-G results alone might be insufficient to exclude M.
tuberculosis infection in these persons.
Practical limitations of the QFT-G include the need for venipuncture and
for transporting the 5-mL blood sample to a qualified laboratory in time
"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
[Bacille Calmette-Guérin] vaccination, and TB screening of health-care
workers and others undergoing serial evaluation for M. tuberculosis
infection," the authors write. "QFT-G usually can be used in place of (and
not in addition to) the TST. A positive QFT-G result should prompt the same
public health and medical interventions as a positive TST result."
The guidelines note that there is no reason to follow a positive QFT-G
result with a TST; instead, those with a positive QFT-G result, regardless
of their symptoms or findings, should be evaluated for TB disease before
LTBI is diagnosed. HIV counseling, testing, and referral is also
recommended because HIV infection increases the suspicion for TB and the
urgency for treating LTBI. Once TB has been ruled out, treatment of LTBI
should be considered.
"For persons with recent contact with persons who have infectious TB,
negative QFT-G results should be confirmed with a repeat test performed 8 -
10 weeks after the end of exposure, as is recommended for a negative TST
result," the authors conclude. "Studies to determine the best time to
retest contacts with negative QFT-G results have not been reported. Until
more information is available, the timing of QFT-G testing should be the
same as that used for the TST."
MMWR Morb Mortal Wkly Rep. 2005;54(RR- 15):49-55