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without also including the detection and treatment of LTBI 1 How should screening for TB and LTBI be prioritized Prioritized or targeted TB screening focuses on screening individuals and populations at highest risk of being infected progressing or reactivating TB disease or having both risks present The purpose of TB screening is to find
Table of Contents,About TB 6, What is latent TB And how is it different from active TB disease 6. What is the meaning of remote TB infection and can QFT distinguish 7. between remote and recent infection,Why is latent TB infection important 7. How should screening for TB and LTBI be prioritized 7. Is latent TB contagious 9, Doesn t everybody in high incidence countries have latent TB 9. About QFT 9,What is QFT 9,What is QFT s intended use 9. What are the clinical situations in which QFT can be used 10. Can QFT distinguish between active TB and LTBI 11,How does it work 12. Why measure interferon gamma 12,How does QFT differ from the TST 12. How long does it take to get QFT results 13,Does a prior TST influence a QFT result 13. What is the minimum time necessary to wait between exposure to 14. M tuberculosis and QFT testing, Why do you include a positive control How does this work 14. What approvals does QFT have 14,What is the evidence supporting QFT 14. Sensitivity and specificity of QFT 15, What is the specificity and sensitivity of QuantiFERON TB Gold 15. Why is it important to have a test with high specificity 15. QFT use in children and the immune suppressed 15, Can IGRA tests be used for infants and children 15. What is the sensitivity of QFT in HIV positive individuals 16. What about indeterminate results in HIV positive individuals 16. FAQ Health Professionals 10 2016 3,QFT procedure 16. What are the steps in administering the test 16, Do the QFT tubes need to be collected in a specific order 17. Why can filling of the tubes occur slowly 17, Why it is necessary to shake the tubes immediately after blood collection 17. What is the effect of incubating the tubes for longer than the 17. recommended time ie if accidently left over the weekend. Interpretation of test results 17,How are QFT test results interpreted 17. How was the cut off value of 0 35 IU ml established 18. Can the amount of IFN measured be correlated to the stage or 18. degree of TB infection,What constitutes a QFT conversion 18. How reproducible are QFT results 19, Why would I see false negative results in patients with active TB 19. Are the results affected by pregnancy 20, What should I do if the QFT result is indeterminate 20. How often does QFT yield an indeterminate result 20. What is the meaning of Mitogen negative responses in healthy individuals 20. Positive QFT results 21, Is a patient with a positive QFT response contagious 21. How should a QFT positive response without information about a recent 21. contact be interpreted, Does a positive QFT result mean there is a greater risk of progressing to 21. active TB than does a positive TST result, Can the level of a positive QFT result be used to give an indication 22. of the likelihood of active disease in the future, Can you explain the occasional change in QFT results for people with 22. responses close to the cut off when the test is repeated. Does a positive QFT result become negative after treatment 23. i e with Isoniazid therapy and if so how quickly does this occur. What does a positive QFT result mean in patients treated for active 23. disease a long time ago,4 FAQ Health Professionals 10 2016. Questions and answers, QuantiFERON TB Gold QFT is a whole blood test that measures the cell mediated immune response of tuberculosis. TB infected individuals Approved by the US Food and Drug Administration FDA and CE marked QFT like the. tuberculin skin test TST can be used as an aid in the diagnosis of latent tuberculosis infection and TB disease This. document has been compiled as a result of common questions posed by healthcare professionals on the use of QFT. Tuberculosis TB is an airborne disease caused by infection with Mycobacterium tuberculosis complex organisms. M tuberculosis M bovis and M africanum The transmission of TB occurs through the inhalation of droplets that are. either coughed or sneezed from an individual infected with active TB disease of the lung active pulmonary TB Not. everyone who becomes infected with TB bacteria develops active TB disease. What is latent TB And how is it different from active TB disease. Latent TB infection LTBI is considered a carrier state of M tuberculosis infection where an individual silently carries. the TB bacteria in their body In LTBI the infection is well contained by the host s immune system Hence unlike active. TB individuals with LTBI are asymptomatic and not contagious to others However this condition may progress or. reactivate to active disease in the future As the development of TB disease depends on a variety of risks and medical. conditions individuals with LTBI are commonly offered preventative therapy to prevent active disease from occurring. Preventative treatment is an important strategy to reduce TB morbidity and rates in many countries. Active TB is a disease state of uncontrolled M tuberculosis growth which occurs when TB bacteria are able to. overcome a person s immune system Active TB can affect any organ of the body but is most commonly a disease of. the lung A person with active TB will often have symptoms which are not specific for tuberculosis e g a cough night. sweats and weight loss Direct detection of M tuberculosis bacilli in sputum or specimen culture is the hallmark of. disease and is considered the gold standard of TB diagnosis A person who has active pulmonary TB and is coughing. with the presence of M tuberculosis in their sputum is infectious. QFT is an assay that detects TB infection by measuring the cell mediated immune response to TB specific antigens It. can be used as a diagnostic aid for M tuberculosis complex infection whether active tuberculosis disease or LTBI. however when using QFT in a person suspected of having active TB it should not replace appropriate microbiological. and molecular investigation QFT cannot distinguish between active and latent TB infection and should therefore never. be used as a sole diagnostic test,FAQ Health Professionals 10 2016 5. What is the meaning of remote TB infection and can QFT distinguish between remote and. recent infection, The term remote infection is an ill defined term that is increasingly being used in the TB community For most it. appears that remote infection relates to old TB infection that may have been cleared by the individual however. some may interpret it as meaning old TB infection that can still reactivate to TB disease As with the TST QFT cannot. distinguish between remote and new infection Individuals with LTBI are asymptomatic and not contagious to others. However this condition may progress or reactivate to active disease in the future As the development of TB disease. depends on a variety of risks and medical conditions individuals with LTBI are commonly offered preventative therapy. to prevent active disease from occurring Preventative treatment is an important strategy to reduce TB morbidity and. rates in many countries,Why is latent TB infection important. It is estimated that up to 10 of people infected with M tuberculosis will develop active TB in their lifetime With an. estimated 2 billion people or one third of the world s population infected the large global reservoir of LTBI represents. a huge pool of contagious disease, Diagnosing LTBI and preventive treatment can significantly reduce the risk of disease and prevent outbreaks from. recent transmission On a global level achieving a significant reduction in the burden of TB cases cannot be achieved. without also including the detection and treatment of LTBI 1. How should screening for TB and LTBI be prioritized. Prioritized or targeted TB screening focuses on screening individuals and populations at highest risk of being infected. progressing or reactivating TB disease or having both risks present The purpose of TB screening is to find cases at. an early asymptomatic phase that is easily curable and find LTBI among individuals who may benefit from preventive. treatment Targeted testing can be applied as follows. 1 Contact investigation Identifying newly infected contacts tops the priority list as the risk of infection is high and. new infection carries a much higher risk of disease progression compared to old or chronic infection 2 Contact. investigation is a WHO recommendation 3,6 FAQ Health Professionals 10 2016. 2 Congregate settings Congregate settings are places where transmission of communicable diseases is a real risk. Focused screening for disease and LTBI prior to entry into congregate settings reduces TB transmission through. early identification of TB and preventive treatment of those at risk of developing disease in that setting. Congregate settings may include, hospitals healthcare institutions higher educational facilities. residential facilities military barracks, prisons correctional facilities certain settings of employment such. renal dialysis units as the mining industry,homeless shelters. 3 Populations with high prevalence of TB infection Targeted screening of individuals that are at high risk of being. infected such as individuals from TB endemic countries entering low burden countries or known populations with. higher TB prevalence such as impoverished homeless persons can make a significant individual and public health. impact especially when TB prevention is focused on those with LTBI that have clinical conditions that increase the. risk of TB disease progression or reactivation, 4 Clinical conditions that increase the risk of developing TB disease Prevention of disease in these individuals with. LTBI prevents the need for long multi drug treatment regimens and protects against developing lung and organ. destruction long term disability death economic loss and transmission of disease to family and those close to the. individual see list below,Medical risks of reactivation. Relative risk reactiviation of TB in various clinical settings. AIDS 110 170 times,HIV Infection 50 110,Solid organ transplant 20 74. Silicosis 30,Recent TB infection 2 years 15,Chronic renal failure 10 25. Carcinoma of head and neck 16, Abnormal chest radiograph with upper lobe fibro nodular disease. typical of healed TB infection,TNF Alpha inhibitor therapy 1 7 9. Glucocorticoid therapy 4 9,Children less than 4 years old 2 2 5. Diabetes mellitus 2 3 6,Underweight BMI 20 2 3,Smoker 1 pack day 2 3. Normal healthy individual 1,Chart adapted from Lobue et al 2. FAQ Health Professionals 10 2016 7, Individuals with LTBI and medical co morbidities should be targeted for LTBI treatment after active tuberculosis has been. excluded by thorough medical evaluation and radiography Similarly patients with TB infection should be targeted for. LTBI treatment before initiation of immune suppressive therapy. This also applies to individuals newly infected from recent exposure to TB such as contacts of known active TB cases. especially child contacts under 5 years of age,Is latent TB contagious. No TB in its latent form cannot spread However it can become active pulmonary TB which is contagious often. before the individual is aware that they have it, Doesn t everybody in high incidence countries have latent TB. No this is a common misconception 1 in 3 people worldwide is thought to be infected with LTBI 4 although there is. significant variance in high incidence countries based on the demographics of the population being studied. What is QFT, QuantiFERON TB Gold QFT is an in vitro laboratory test that measures responses to TB specific peptide antigens in. whole blood It is an indirect test for M tuberculosis infection A modern replacement to the tuberculin skin test TST. QFT provides clinicians with an accurate reliable and efficient tool for aiding the diagnosis of TB infection. QFT is highly specific and sensitive a positive result is strongly predictive of true infection with M tuberculosis. However like the TST and other Interferon gamma release assays IGRAs QFT cannot distinguish between active. tuberculosis disease and LTBI and is intended for use in conjunction with risk assessment radiography and other. medical and diagnostic evaluations,What is QFT s intended use. QFT is an in vitro laboratory diagnostic test using a whole blood specimen It is intended for use as a diagnostic. aid for M tuberculosis complex infection whether active tuberculosis disease or LTBI and is intended for use in. conjunction with risk assessment radiography and other medical and diagnostic evaluations Like the TST or any. diagnostic aid QFT should never be used as a stand alone test for diagnosis or treatment of active tuberculosis. and a negative QFT result should be used with caution when the patient is suspected of having active TB or is. immunosuppressed Like any other diagnostic aid QFT cannot replace clinical judgement. 8 FAQ Health Professionals 10 2016, What are the clinical situations in which QFT can be used. QFT can be used for those being evaluated for possible M tuberculosis infection whether active disease or LTBI. According to the US Centers for Disease Control and Prevention CDC 4 QFT can be used in many situations. CDC Specific Recommendations, IGRAs may be used in place of but not in addition to a TST in all situations in which the CDC recommends TST as. an aid in diagnosing M tuberculosis infection, IGRAs is preferred for testing persons from groups that historically have poor rates of return for TST reading. IGRAs is preferred for testing persons who have received Bacille Calmette Guerin BCG as a vaccine or for cancer. Either an IGRA or a TST may be used without preference to test recent contacts of persons with infectious. tuberculosis with special considerations for follow up testing In contact investigations negative results obtained prior. to 8 weeks typically should be confirmed by repeat testing 8 10 weeks after the end of exposure. Either an IGRA or a TST may be used without preference for periodic screening that addresses occupational. exposure to TB eg surveillance programs for healthcare workers HCW with special considerations regarding. conversions and reversions see full CDC guideline 4 Two step testing is not required because IGRA testing does. not boost subsequent test results, TST is preferred for testing children younger than 5 years old due to the relatively few published reports. documenting the performance of IGRAs in young children However use of an IGRA in conjunction with TST may. increase diagnostic sensitivity in this age group, While routine testing with both TST and an IGRA is not recommended results from both tests may be useful in the. following situations when the initial test is NEGATIVE. hen the risk of infection the risk of progression and the risk of a poor outcome are increased such as when. persons with HIV infection or children 5 years old are at increased risk for M tuberculosis infection or. hen there is clinical suspicion of active tuberculosis such as in persons with symptoms signs and or. radiographic evidence suggestive of active tuberculosis and confirmation of M tuberculosis infection is desired. While routine testing with both TST and an IGRA is not recommended results from both tests may be useful in the. following situations when the initial test is POSITIVE. dditional evidence of infection is required to encourage compliance such as in foreignborn healthcare workers. who believe their positive TST is due to BCG or, in healthy persons who have a low risk of both infection and progression. Repeating an IGRA or performing a TST may be useful when the initial IGRA result is indeterminate and a reason for. testing persists,FAQ Health Professionals 10 2016 9. Decisions should not be based on IGRA or TST results alone A diagnosis of M tuberculosis infection and the. decisions about medical or public health management should include epidemiological historical and other clinical. information when using IGRA or TST results, Persons with a positive TST or IGRA result should be evaluated for the likelihood of M tuberculosis infection for risks. of progression to tuberculosis disease if infected and for symptoms and signs of tuberculosis disease. Neither an IGRA nor TST can distinguish LTBI from TB disease A diagnosis of LTBI requires that tuberculosis disease. be excluded by medical evaluation which should include checking for suggestive symptoms and signs a chest. radiograph and when indicated testing of sputum or other clinical samples for the presence of M tuberculosis. In persons with symptoms signs or radiographic evidence of TB disease and in those at increased risk of. progression to tuberculosis disease if infected a positive result with either an IGRA or TST may be taken as evidence. of M tuberculosis infection However negative IGRA or TST results are not sufficient to exclude infection in these. persons especially in those at increased risk of a poor outcome if disease develops and clinical judgment dictates. when and if further diagnostic evaluation and treatment are indicated. Both the standard qualitative test interpretation and the quantitative assay measurements should be reported. together with the criteria for test interpretation. As with the TST IGRAs generally should not be used for testing persons who have a low risk of infection and a low. risk of disease due to M tuberculosis, IGRAs or TST should be used as aids in diagnosing infection with M tuberculosis These tests may be used for. surveillance purposes or to identify persons who are likely to benefit from treatment. IGRAs should be performed and interpreted according to established protocols using FDAapproved test formats. IGRAs should be performed in compliance with Clinical Laboratory Improvement Amendment CLIA standards. For BCG vaccinated persons who are not at increased risk for developing TB if infected TST reactions 15mm may. be reasonably discounted as false positives if the individual has a clearly negative IGRA result. If two different tests are performed a positive result from either test should be taken as evidence of infection for. those with suspected active TB or at high risk of progression. Can QFT distinguish between active TB and LTBI, Like the TST and other IGRA tests QFT cannot distinguish between active TB and LTBI Anyone testing positive should. be assessed for active TB with a medical evaluation chest radiograph and other tests indicated by the clinical. symptoms and medical evaluation,10 FAQ Health Professionals 10 2016. How does it work, QFT measures cell mediated immune CMI response in TB infected individuals T cells of these individuals are sensitized. to TB and respond to stimulation with peptides simulating those expressed by the TB causing bacteria by secreting a. cytokine called interferon gamma IFN, QFT uses peptides from three proteins made almost exclusively by M tuberculosis and the other mycobacteria of the. tuberculosis complex Those proteins are absent from all BCG vaccine preparations and from most non tuberculous. mycobacteria NTM with the exceptions of M kansasii M marinum and M szulgai 5. Special blood collection tubes coated with peptides from these three TB antigenic proteins are used for blood collection. and incubation of the patient s blood IFN is released when the blood from infected individuals is incubated with the. antigens 16 24 hours at 37 C This is not the case for individuals free from infection An ELISA laboratory test is. used to detect and quantify the amount of IFN that has been released. Why measure interferon gamma, M tuberculosis is an intracellular pathogen primarily residing within macrophages During the latent phase of the. infection little if any antigen is expected to leave the macrophages to be available to B cells to stimulate a humoral. antibody response However processed antigen is presented by infected macrophages to antigen specific T cells and. triggers a cascade of immune responses leading to the generation of specialized effector T cells which will circulate in. the individual s blood stream, When blood is taken from an infected individual and stimulated with M tuberculosis specific antigens effector T cells. release the cytokine IFN The production and subsequent measurement of IFN by a rapid ELISA forms the basis of. How does QFT differ from the TST,Sensitivity and specificity. The tuberculin purified protein derivative PPD used in the TST is an ill defined mix of proteins and protein fragments. of which some are specific for M tuberculosis complex However the vast majority have homologs that are shared. with environmental mycobacteria and BCG vaccine strains It is largely for this reason that the TST test has poor. specificity especially in BCG vaccinated individuals. The TST assesses in vivo delayed type hypersensitivity Type IV whereas QFT measures in vitro release of IFN The. TST measures response to PPD a polyvalent antigenic mixture whereas QFT measures responses to a well defined mix. of synthetic peptides simulating three antigenic proteins that are specific for tuberculosis. Unlike the TST an uninfected individual is not subject to boosting with QFT Moreover QFT is not confounded by BCG. vaccination and most common environmental NTM except M kansasii M marinum and M szulgai. FAQ Health Professionals 10 2016 11,Handling and interpretation. There are numerous differences between the TST and QFT. The TST requires skill in placing PPD whereas QFT requires routine phlebotomy. The TST requires a person to return to have their test read 48 to 72 hours after administration QFT requires only. one visit to a healthcare provider for blood collection. The TST is subjective in its interpretation in respect to both measuring the induration on the individual s arm and in. deciding what cut off to apply QFT is an objective laboratory based test with interpretation determined by analysis. of ELISA data by QFT analysis software, Positive QFT results can be provided confidentially whereas a positive inflammatory TST response can be a source. of stigma since it is often visible especially if redness accompanies the induration. Individuals can confound their own TST with something as simple as a hot shower or low dose over the counter. corticosteroid cream,How long does it take to get QFT results. This varies and depends on how frequently the laboratory in your area carries out the test Results can be available in. 24 hours Unlike the TST individuals do not need to return 2 3 days later in order to have the test read. Does a prior TST influence a QFT result, There is some conflicting evidence that suggests that a prior TST can induce a positive QFT result in an uninfected. individual One paper 6 based on the results from only 3 individuals speculates that boosting does occur but. this has not been supported in much larger studies 7 8 Reports by Leyten et al 7 and Richeldi et al 8 clearly. demonstrate that a TST placed 3 days prior to QFT and up to 12 weeks later does not induce positive responses in. those uninfected The largest study on the effect of the TST on a QFT response was part of a CDC US Military study in. Navy recruits Data from this study reviewed by the US FDA and presented in the QFT Package Insert found. that in 530 subjects tested twice 4 to 5 weeks apart the reproducibility of QFT was 98 5 Five recruits changed. from positive to negative and 3 became QFT positive. The above findings are in agreement with the general knowledge of how an immune response is generated It would. not be expected that uninfected individuals would mount a primary cellular immune response to the extremely small. amounts of the TB specific antigens used in QFT that are present in the aqueous tuberculin injected However it is. possible that even very small amounts of ESAT 6 CFP 10 and TB7 7 p4 may be present in tuberculin and could. boost responses of individuals infected with M tuberculosis but not from BCG vaccination There is evidence of this. possibility in the studies published to date To avoid a boosted response QFT should be administered concurrently or. no later than 3 days after a TST 9, In contrast to QFT boosting is a common phenomenon when a TST is repeated Injection of tuberculin for the TST can. boost subsequent TST responses due to remote TB infection as well as infection with NTM or vaccination with BCG. 12 FAQ Health Professionals 10 2016, What is the minimum time necessary to wait between exposure to M tuberculosis and QFT. Available data suggests that QFT returns a positive result at least as quickly as the TST following recent infection A. Japanese study concluded that the standard 3 month follow up used for the TST should be used for QFT In that study. individuals were tested at the time of diagnosis of the index and at 2 3 4 and 6 months Of those who developed. positive responses 2 contacts were positive at the time of diagnosis of the index 5 more were positive at 2 months. and 1 more at 3 months 10 In a contact investigation of Swiss military recruits 14 out of 15 contacts were positive. when tested 8 weeks after exposure 11, The CDC guidelines on the use of QFT recommend that recent contacts who test QFT negative prior to 8 weeks after. the end of exposure be retested 8 to 10 weeks later similar to the recommendations for the TST Many other national. guidelines recommend a similar approach, Why do you include a positive control How does this work. The Mitogen tube is used as an IFN positive control for each specimen tested The Mitogen tube also serves as a. control for correct blood handling and incubation The mitogen used is phytohaemagglutinin P PHA which is a non. specific stimulator of T cells While it is a direct activator of T cells unpublished data suggest that macrophages are. also required for it to activate T cells, A low IFN response to Mitogen 0 5 IU ml indicates an indeterminate result when a blood sample also has a. negative response to the TB antigens This pattern may occur with insufficient lymphocytes reduced lymphocyte activity. due to improper specimen handling or an inability of the patient s lymphocytes to generate IFN. What approvals does QFT have, QFT is approved for use by the FDA and has been CE marked allowing it to be sold freely in the EU The test has. also been granted regulatory approval in Japan Canada Korea and many other countries Some countries do not. require regulatory approval of in vitro diagnostic tests. What is the evidence supporting QFT, Over 1100 publications in numerous international journals support the use of QFT in different clinical settings. For a complete and up to date list of clinical papers and guidelines please refer to www gnowee net the online. QuantiFERON library,FAQ Health Professionals 10 2016 13. Sensitivity and specificity of QFT, What is the specificity and sensitivity of QuantiFERON TB Gold. The specificity of QuantiFERON TB Gold has consistently shown to be 99 in low risk individuals 12 Specificity. is the probability that the test indicates a person does not have the disease or infection when that person is disease. The sensitivity of QuantiFERON TB Gold is as high as 92 in individuals with active disease but varies depending on. the setting and extent of TB disease 12 Sensitivity is the probability that the test indicates a person has the disease. or infection when in fact that person does have the disease. The TST has traditionally been used to screen populations for LTBI however there is no gold standard for diagnosing. LTBI All screening tests are designed to identify the possibility that a disease might be present and to prompt further. evaluation in those who screen positive For LTBI the only gold standard is the later development of active TB QFT has. been shown to be 4 times better than TST in detecting the individuals who will progress to active TB disease 13 and. this combined with its 99 specificity provides confidence that QFT is detecting those truly infected. Why is it important to have a test with high specificity. Specificity is defined as the probability that the test indicates an individual does not have the disease or infection. when in fact they are disease free QFT has been shown to have 99 specificity compared to lower than 70 for. the TST in some settings, In many countries targeted testing policies are in place to screen individuals who are at increased risk of having LTBI. such as those mentioned on page 7 Without high specificity in these situations there will often be more false positive. than true positive results and most people treated with latent TB drugs will be receiving drugs they do not need with. the potential for adverse side effects from unnecessary therapy Additionally this wastes valuable resources and funds. following up individuals who do not need treatment. QFT use in children and the immune suppressed,Can IGRA tests be used for infants and children. Evidence shows that QFT performs as well in children as it does in adults and there is no apparent loss of performance. in children under 5 years 14 18 For detection of LTBI QFT is as sensitive as the TST and more specific 17 In a. study of children who lived in close contact with smearpositive adult TB patients QFT detected more children infected. with TB than did the TST Positive QFT results showed significant correlation with smear status of the infected adults. whereas TST did not 17 QFT has also been shown to be more accurate than the TST in detecting who will progress. to active TB disease with very high accuracy among pediatric contacts 13. Disclaimer The performance of the USA format of the QFT test has not been extensively evaluated with specimens from individuals. younger than age 17 years,14 FAQ Health Professionals 10 2016. QFT has been shown to be effective in children less than 6 months of age and in children with bacteriologically. confirmed TB the sensitivity of QFT was 93 16 However caution is always needed when interpreting a negative. result in a young child suspected of having active TB. What is the sensitivity of QFT in HIV positive individuals. Studies suggest that QFT is more sensitive and specific than the TST for detecting M tuberculosis infection in HIV. positive people 19 21 In an HIV TB co infected population the sensitivity of QFT is 63 85 compared to. 15 46 for the TST 22 23, In HIV infected AIDS patients with CD4 T cell counts less than 200 l there may be an increase in the number of. people who do not respond to the Mitogen positive control 19 24 These people are deemed indeterminate by. QFT which means a result cannot be given which is appropriate if they do not have a sufficient immune response. to measure Most people with indeterminate responses due to low CD4 T cells counts test negative by the TST which. does not have a control for immune status Indeterminate results are usually treated as negative in sensitivity estimates. meaning that in studies of patients with low CD4 counts lower sensitivity estimates will be reported. What about indeterminate results in HIV positive individuals. Studies to date have shown that indeterminate QFT results are more prevalent in individuals with a CD4 count 200. l especially when the CD4 count is under 100 l 19 21 25 Indeterminate results are likely more frequent in HIV. patients with active TB than LTBI 25 Individuals with a CD4 count 100 l are severely immune suppressed and the. TST is also generally negative in these individuals independent of infection status. Disclaimer The performance of the USA format of the QFT test has not been extensively evaluated with specimens from individuals who. have impaired or altered immune functions such as those who have HIV infection or AIDS. QFT procedure,What are the steps in administering the test. 1 It is best to confirm arrangements for testing with a qualified laboratory which can deliver the necessary sampling. 2 Draw a 1 ml sample of blood from a patient directly into each of the three blood collection tubes following the. manufacturer s instructions The black mark on the side of the tubes indicates the 1 ml fill volume QFT blood. collection tubes have been validated for volumes ranging from 0 8 ml and 1 2 ml If the level of blood in any tube. is not close to the indicator line it is recommended to obtain another blood sample As a guide the picture on the. left illustrates the approved fill range, 3 Assure delivery to the laboratory for incubation as soon as possible and within 16 hours after blood draw Keep. at room temperature 22 5 C before incubation Or alternatively at the collection site incubate the tubes standing. upright for 16 to 24 hours at 37 C before shipping them to the laboratory at room temperature or refrigerated. within 3 days, For comprehensive instructions for use refer to the QFT ELISA package insert.