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MOLECULAR DIAGNOSIS OF TB AND IGRA PRESENTED BY : Dr. Kiran N

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1 MOLECULAR DIAGNOSIS OF TB AND IGRA PRESENTED BY : Dr. Kiran N
MOLECULAR DIAGNOSIS OF TB AND IGRA PRESENTED BY : Dr. Kiran N. PG Student Chest & Tuberculosis Govt. Medical College, Patiala

2 Molecular Diagnostics Why?
Detection and Diagnosis uncultivable or difficult to culture need for rapid diagnosis inadequacy of phenotypic methods (biochemical) Prognosis and management need for quantitative information (bacterial load) susceptibility testing (drug resistance) without culture - Molecular resistance testing

3 METHODS OF DIAGNOSIS OF PULMONARY TUBERCULOSIS
1)DIRECT METHODS: Detects mycobacteria and its products 2)INDIRECT METHODS : Antigen and Antibody Detection 3)RADIO-DIAGNOSIS :CXR,CT AND MRI DIRECT METHODS 1)Direct Microscopy -ZN stain, Kinyoun, Flurochrome. 2)Culture -Traditional, Rapid methods. 3) Detection of DNA or RNA of mycobacterial origin i,e (molecular methods) includes - PCR, LAMP, TAA / NAA, LCR, Fast Plaque.

4 INDIRECT METHODS 1)Antibody detection : TB STAT-PAK ELISA Insta test TB 2) Antigen detection : TB MPB 64 patch test. Quantiferon-GOLD test. 3) Biochemical Assays : ADA Bromide Partition Gas Chromatography

5 MOLECULAR DIAGNOSIS OF TUBERCULOSIS
Rapid and sensitive tools for the diagnosis of tuberculosis are needed, due to the increased incidence of tuberculosis epidemics and the length of time required by classical diagnostic tests, especially among human immunodeficiency virus (HIV)-infected patients. In this context, the recent advances in cloning and characterization of M. tuberculosis genes has allowed the application of basic molecular biology techniques to the examination of clinical samples, such as sputum and bronchoalveolar lavage (BAL), for the molecular diagnosis of tuberculous infection. By using the polymerase chain reaction (PCR) for the amplification of mycobacterial nucleic acids and nonradiometric revelation techniques, the time required for the identification of mycobacteria has been considerably shortened (24-48 h), in comparison to the time required by microbiological tests

6 Dr.T.V.Rao MD

7 MOLECULAR TESTS FOR DETECTION OF NUCLEIC ACIDS
The majority of molecular tests have been focused on detection of nucleic acids, both DNA and RNA, that are specific to Mycobacterium tuberculosis, by amplification techniques such as polymerase chain reaction (PCR); and detection of mutations in the genes that are associated with resistance to anti tuberculosis drugs by sequencing or nucleic acid hybridization. Recent developments in direct and rapid detection of mycobacteria, with emphasis on M. tuberculosis species identification by 16S rRNA gene sequence analysis or oligohybridization and strain typing, as well as detection of drug susceptibility patterns, all contribute to these advance

8 Polymerase Chain Reaction
PCR was invented by Kary Mullis in 1983 (Nobel Prize for Chemistry in 1993) PCR is a technique that takes a small amount of a specific DNA sequence and amplifies for further testing. It`s like a “molecular photocopier”.

9 Polymerase Chain Reaction (PCR)
Essentially PCR is a way to make millions of identical copies of a specific DNA sequence , which may be a gene, or a part of a gene, or simply a stretch of nucleotides with a known DNA sequence, the function of which may be unknown. A specimen that may contain the DNA sequence of interest is heated to denature double stranded DNA. Specific synthetic oligonucleotide primers bind to the unique DNA sequences of interest and a heat stable DNA polymerase (Thermus aquaticus) extends the primer to create a complete & complimentary strand of DNA.

10 This process is repeated sequentially times, thereby creating millions of copies of target sequence. The amplified sequence can then be detected by agarose gel electrophoresis.DNA sequence used include: 1) 65 Kd antigen (HSPs): Used earlier Heat shock protein believed to be distinct from other bacterial HSPs. This gene is identical in all species of mycobacteria. Therefore unsuitable for detecting M.tb, particularly in areas where species like M.avium or M.kansasii are prevalent.

11 2) IS6110 : It is a transposon which are self replicating stretches of DNA. Function not known. This sequence has been found in the M.tb complex organisms (M.tb, M.africanum, M.microti, M.bovis). IS6110 sequence generally occurs only once in M.bovis but is found as often as 20 times in certain strains of M.tb, thus offering multiple targets for amplification PCR can detect even a fraction of a bacilli.

12 Mycobacterium tuberculosis genome
Dr.T.V.Rao MD

13 Ingredients of Polymerase Chain Reaction
Primers: µM Deoxy-nucleotides triphosphate (dNTPs): µM nucleotides Co-factors: Cations: MgCl2 mM 1.5-6 Buffer pH DNA polymerase: U Target DNA:  1 µg

14 Chromosome and Desoxyribo-Nucleic-Acid
Zellkern nucleus Zelle cell DNA DNA - Basenpaare base pairs double helix Doppelhelix

15 Primers Primers are target sequence specific oligonucleotides that serve as template for the DNA polymerase Forward and reverse primers flanking the target sequence allow both DNA strands to be copied simultaneously in both directions.

16 Three steps of PCR: Denaturation, annealing and extension

17 Role of PCR in pulmonary TB :
Detects nearly all smear +ve and culture +ve cases. Useful technology for rapid diagnosis of smear –ve cases of active TB. Able to identify 50-60% of smear -ve cases; this would reduce the need for more invasive approaches to smear - ve cases Distinguish M.tb from NTM in smear +ve cases as IS6110 sequence is not found in NTM. Should not be used to replace sputum microscopy. Sensitivity, specificity, & PPV for PCR is 83.5%, 99% & 94.2% respectively

18 Role in Extrapulmonary TB
Limited Role No comprehensive large series comparing the yield of PCR with other available approaches has been published. But at present, it is valuable adjunct in the diagnosis of TBM, pleurisy, pericardial TB & other condition in which yield of other tests are low

19 Disadvantages Very high degree of quality control required.
Variation from lab to lab remain significant. In pts. on ATT, PCR should not be used as an indicator of infectivity as this assay remains +ve for a greater time than do cultures High false +ve results in patients previously treated with ATT in contacts of sputum +ve active cases. High Cost

20 Real Time PCR replacing older Methods

21 LAMP* Loop-mediated isothermal amplification.
It is a novel nucleic acid amplification method in which reagents react under isothermal conditions with high specificity, efficiency, and rapidity. LAMP is used for detection of M.tb complex, M.avium, and M.intracellulare directly from sputum specimens as well as for detection of culture isolates grown in a liquid medium (MGIT) or on a solid medium (Ogawa’s medium). This method employs a DNA polymerase and a set of four specially designed primers that recognize a total of six distinct sequences on the target DNA. Species-specific primers were designed by targeting the gyrB gene. Simple procedure, starting with the mixing of all reagents in a single tube, followed by an isothermal reaction during which the reaction mixture is held at 63°C. 60-min incubation time.

22 ADVANTAGES: Due to its easy operation without sophisticated equipment, it will be simple enough to use in: Small-scale hospitals, Primary care facilities Clinical laboratorie in developing countries. Difficulties : Sample preparation Nucleic acid extraction Cross-contamination

23 TMA / NAA Transcription Mediated Amplification (TMA) / Nucleic Acid Amplification (NAA). These techniques use chemical rather than biological amplification to produce nucleic acid. Test results within few hours. Currently used only for respiratory specimens.

24 Nucleic acid amplification assays
NAA assays amplify M. tuberculosis-specific nucleic acid sequences using a nucleic acid probe. The sensitivity of the NAA assays currently in commercial use is at least 80% in most studies Require as few as bacilli from a given sample NAA assays are also quite specific for M. tuberculosis, with specificity in the range of 98% to 99%.

25 NAAs- various types AMPLICOR M. TUBERCULOSIS assay
Amplified M.tuberculosis Direct (AMTD2) assay LCx MTB assay, ABBOTT LCx probe system BD ProbeTec energy transfer (ET) system (DTB) INNO-LiPA RIF.TB assay

26 NAAs- various types Dr.T.V.Rao MD

27 NAA- Limitations They are able to detect nucleic acids from both living and dead organisms so in pts on ATT, PCR should not be used as an indicator of infectivity as this assay remains positive for a greater time, than do cultures A major limitation of NAA tests is that they give no drug-susceptibility information. NAA should always be performed in conjunction with microscopy and culture

28 DISADVANTAGES : 1) Poor sensitivity in smear –ve samples
2) Labour intensive 3) Highly trained personnel required & dedicated labour space because it requires atleast 3 separate rooms to avoid cross contamination. Hence suitable only for IRL.

29 Ligase Chain Reaction It is a variant of PCR, in which a pair of oligonucleotides are made to bind to one of the DNA target strands, so that they are adjacent to each other. A second pair of oligonucleotides is designed to hybridize to the same regions on the complementary DNA. The action of DNA polymerase and ligase in the presence of nucleotides results in the gap between adjacent primers being filled with appropriate nucleotides and ligation of primers. It is mainly being used for respiratory samples, and has a high overall specificity and sensitivity for smear +ve and –ve specimens.

30 MDR TB MDR-TB is defined as resistance to isoniazid and rifampicin, with or without resistance to other first line drugs (FLD). In the Global TB Report 2011, WHO estimated that among the 1.5 million RNTCP-notified cases of pulmonary TB in India in 2010, approximately 64,000 cases of MDR TB could be diagnosed. MDR TB is important because patients with this type of drug resistance respond extremely poorly to standard anti-TB treatment with first-line drugs. MDR TB requires relatively costly laboratory diagnosis and treatment for at least two- years with drugs that are expensive, toxic, and not particularly potent. A case of MDR TB is about times more expensive to manage than a case of drug-sensitive TB, and patient suffering is magnified.

31 MDR Suspect Criteria Criteria C – in addition to Criteria B :
Criteria A- All features of new TB cases. Smear +ve previously treated cases who remain smear +ve at 4th month onwards. All pulmonary TB cases who are contacts of known MDR TB case. Criteria B – in addition to Criteria A : All smear +ve previously treated pulmonary TB cases at diagnosis. Any smear +ve follow up result in new or previously treated cases. Criteria C – in addition to Criteria B : All smear –ve previously treated pulmonary TB cases at diagnosis. HIV TB co-infected cases at diagnosis.

32 Molecular methods for drug resistance
Rifampin (RIF) – Binds to β subunit of RNA polymerase (rpoB) – 96% of resistant Mtb isolates have mutations in 81-bp region. – Four (4) mutations . 75% of resistant clinical isolates • Isoniazid (INH) . two genes – katG and inhA % • Pyrazinamide . pncA . 70% • Streptomycin . rpsL % • Ethambutol .embB . 70%

33 Causes of Drug Resistance in TB
Lack of understanding of why long term therapy with multiple drugs is necessary Non-adherence to therapy by patients Incorrect drug prescribing by providers Poor quality drugs Erratic supply of drugs Malabsorption of drugs primarily due to symptoms of HIV/AIDS

34 Development of drug resistance in M. tuberculosis
The mycobacterial cell is surrounded by a specialized, highly hydrophobic cell wall that results in decreased permeability to many antimicrobial agents. Resistance of M tuberculosis to antimycobacterial drugs is the consequence of naturally occuring, spontaneous mutations in genes that encode either the target of the drug, or enzymes that are involved in drug activation. Resistance-associated mutations have been described for all first-line drugs (isoniazid, rifampin, pyrazinamide, ethambutol, and streptomycin).

35 Development of multi-drug resistant tuberculosis
No single genetic alteration has yet been found that results in the MDR phenotype (defined as resistance at least to INH and RMP). MDR develops by sequential acquisition and selection of mutations at different loci, usually because of inappropriate patient treatment. Inappropriate treatment may lead to disease progression. Disease progression will increase the bacterial load and the risk of naturally occurring mutations. Because MDR strains are the result of cumulative mutations, growth of M tuberculosis can successfully be controlled in the host by concomitant treatment with more than one drug. Thus, treatment regimens that consist of three to four drugs are used routinely to treat patients with tuberculosis.

36 Isoniazid resistance and katG
INH is a pro-drug that requires activation in INH-susceptible mycobacterial species. the activation of INH results in a number of highly reactive compound that are capable of damaging the mycobacterial cell wall. INH-resistant clinical isolates frequently loose their catalase-peroxidase activity (Middlebrook et al., 1954) Association of this enzyme with INH activation was proven when the mycobacterial catalase-peroxidase gene (katG) was cloned and sequenced. (Zhang et al., 1992) Mutations in this gene were found in % of high INH-resistant clinical isolates. The most common mutation that was found was the Ser315Thr mutation.

37 Isoniazid resistance and virulence
The Ser315Thr mutation results in an enzyme without the ability to activate INH, but retains approximately 50% of its catalase-peroxidase activity. This altered catalase- peroxidase provides high-level resistance to INH, while retaining a level of oxidative protection against host antibacterial radicals. Isolates that carry other, mutations in katG are exhibiting varying levels of INH-resistance and catalase- peroxidase activity. Lysosomes with free oxigene radicals Phago-lysosomes with inactivated MTB MTB Phagosome with viable MTB

38 Isoniazid resistance and inhA
INH blocks the synthesis of cell- wall mycolic acids, the major components of the envelope of M tuberculosis. One intracellular target of the drug is fatty-acid enoyl-acyl carrier protein reductase (InhA). (Basso et al., 1998) This enzyme is involved in synthesis of mycolic acids. Mutations in the promoter region of the gene (inhA) encoding this enzyme result in over-expression of the protein. The over-expressed enzyme may counter-balance the effect of INH and will result in a low- level resistance to the drug.

39 Rifampin resistance One of the main reasons for treatment failure and fatal clinical outcome in tuberculosis patients is resistance to RMP. RMP exhibits a significant early bactericidal effect on metabolically active M tuberculosis, and excellent late sterilizing action on semidormant organisms undergoing short bursts of metabolic activity. While monoresistance to INH is common, monoresistance to RMP is rare. RMP resistance occurs most often in strains that are also resistant to INH, thus, RMP resistance can be used as a surrogate marker for MDR. RMP inhibits mycobacterial transcription by targeting DNA- dependent RNA polymerase.

40 Rifampin resistance and rpoB
Resistance to RMP is due to mutations in a well-defined, 81 base pair (27 codons) central region of the gene that encodes the β-subunit of RNA polymerase (rpoB). More than 96% of the rifampin-resistant strains contain a mutation in this 81 bp region of rpoB. The most common mutations (65–86%) alter either codon 526 or codon 531, and result in high-level resistance to RMP. Alterations in other codons result in low-level resistance. Rare mutations associated with rifampin resistance have also been found in the amino-terminal region of rpoB.

41 MOLECULAR METHODS OF DIAGNOSING DRUG RESISTANT TB
Phenotypic methods: in liquid/solid media Genotypic methods: Gene xpert/LPA PHENOTYPIC METHODS 1)Commercial methods Done on liquid or solid media Can be direct/indirect type. Indirect type has 3 variants: absolute concentration/resistant ratio/proportion method Can be used for 1st line/2nd line DST

42 2)Non commercial methods
Less expensive than commercial systems but are prone to errors due to lack of standardization and local variations in methodology. These include a)MODS (microscopic observation drug susceptibility) a microcolony method in liquid culture(middlebrook 7H9 broth) based on inoculation of specimens into drug-free and drug- containing media, followed by microscopic examination of early growth Recommended as direct or indirect tests for rapid screening of patients suspected of having MDR-TB.

43 b)COLORIMETRIC METHODS
Indirect testing methods based on the reduction of a coloured indicator added to liquid culture medium on a microtitre plate after exposure of M. Tuberculosis strains to anti-TB drugs in vitro. Recommended as indirect tests on M. tuberculosis isolates from patients suspected of having MDR-TB, although the time to detection of MDR is not faster (but less expensive) than conventional DST methods with commercial liquid culture or molecular LPA. The indicators that have been used to date include tetrazolium salts (XTT and MTT), Alamar blue and resazurin.

44 c)NITRATE REDUCTION ASSAY (NRA)
A direct or indirect method on solid culture based on the ability of M.tuberculosis to reduce nitrate, which is detected by a colour reaction Recommended as direct or indirect tests for screening patients suspected of having MDRTB, although the time to detection of MDR in indirect application is not faster than conventional DST methods with liquid culture.

45 GENOTYPIC METHODS LPA Gene Xpert /RIF

46 LPA(Line Probe Assay) It is a genotypic method use PCR and reverse hybridization with specific oligonucleotide probes fixed to nitrocellulose strips in parallel lines therefore often reffered to as “strip tests”. which detects resistance to Both H&R Sensitivity for R is 97%, H is 90% Specificity for R& H is 99% Results within 48 hours

47 Differences InnoLiPA Rif Hain GenotType MTBDRplus
It targets 16s - 23s rRNA gene space region. It detects only R resistance. Hain GenotType MTBDRplus It targets 23s rRNA gene space region. It detects both R and H resistance.

48 TB Molecular Identification
AVAILABLE SYSTEMS (Commercial): Hain GenotType MTBDRplus InnoLiPA Rif ADVANTAGES of molecular testing: Rapid results Specific information Can be done in presence of contaminants Less biohazard risk involved DISADVANTAGES of molecular testing: Expensive Dedicated equipment Technical expertise required

49 Denaturation of the amplified DNA products into single-strands
Rapid molecular detection of INH and RMP resistance: Line – Probe Assay Methodology DNA isolated from processed original specimen or from cultured bacterial cells Multiplexed amplification (PCR) of mycobacterial DNA using biotin labeled primers Denaturation of the amplified DNA products into single-strands Hybridization of the denatured DNA to probes on a membrane strip Enzyme-mediated detection of bands where DNA products have bound to strip

50 Polymerase Chain Reaction

51 MTBDR plus strip for Identification of MTB complex
and resistance to RMP and/or INH

52 Rifampicin resistance: rpoB gene
rpoB wild type probes: WT 1 to WT 8 rpoB mutation-specific probes: MUT D516V, H526Y, H526D, S531L Detection of mutations: missing of wildtype signals presence of common mutation-specific signals

53 High-level Isoniazid resistance: katG gene
Mutations in katG and the corresponding wild type and mutation probes missing wild type probe analyzed codon mutation probe mutation katG WT katG MUT1 S315T1 katG MUT2 S315T2

54 High-level Isoniazid resistance: katG gene
Mutations in katG and the corresponding wild type and mutation probes missing wild type probe analyzed codon mutation probe mutation katG WT katG MUT1 S315T1 katG MUT2 S315T2

55 High-level Isoniazid resistance: katG gene
Mutations in katG and the corresponding wild type and mutation probes missing wild type probe analyzed codon mutation probe mutation katG WT katG MUT1 S315T1 katG MUT2 S315T2

56 Low-level Isoniazid resistance: inhA gene
Mutations in the inhA promotor region and the corresponding wild type and mutation probes

57 Xpert MTB/RIF assay (CBNAAT-cartridge based NAA test)
It is an automated PCR diagnostic test that can detect presence of M.tb & resistance to RIFampicin(by detecting mutation in 81bp region) It is automatic,fast & sensitive Accurate diagnosis is obtained in 1hr 45 mins by adding a reagent to the sputum sample & 15mins later its pippeted into a cartridge that is inserted into the diagnostic instrument

58 Xpert MTB/RIF Dual PCR reactions— sample-processing PCR is followed by hemi-processing PCR —increase the test’s sensitivity and specificity: according to the results published in NEJM, the PCR test was 98.2% sensitive in patients with smear- positive, culture-positive TB. And, because it is automated, there is little technical training needed to administer the test.

59 Other molecular methods include: 3) DNA microarrays
Based on the principle of hybridization Detect Rifampicin resistance only Analysis large amounts of DNA sequences 4)Molecular beacons They are nucleic acid hybridization probes d desinged to bind to target DNA sequences in regions such as rpoB ,where resistance mutations are known to occur. Sensitive enough to detect 2 bacilli, Results in 3 hours

60 5)Single-strand conformation polymorphism (SSCP) 6)Fluorescence resonance energy transfer (FRET) probes 7)Flow cytometry CONCLUSION: LPA is applicable on sputum+ve specimens only.Gene Xpert cant monitor progress of treatment. HENCE PHENOTYPIC CULTURE REMAINS THE GOLD STANDARD

61 Interferon-gamma release assays for latent tuberculosis infection
They are surrogate markers of Mycobacterium tuberculosis infection and indicate a cellular immune response to M. tuberculosis. IGRAs cannot distinguish between latent infection and active tuberculosis (TB) disease, and should not be used for diagnosis of active TB, which is a microbiological diagnosis. A positive IGRA result may not necessarily indicate active TB, and a negative IGRA result may not rule out active TB. IGRAs are not affected by Bacille Calmette-Guérin (BCG) vaccination status, IGRAs are useful for evaluation of LTBI in BCG-vaccinated individuals, particularly in settings where BCG vaccination is administered after infancy or multiple (booster) BCG vaccinations are given. IGRAs appear to be unaffected by most infections with environmental nontuberculous mycobacteria

62 Blood Assays for M. tuberculosis
Interim Caribbean Guidelines for the Prevention, Treatment, Care, and Control of Tuberculosis Module Version Blood Assays for M. tuberculosis QuantiFERON®-TB Gold In-Tube (Cellestis Ltd, Victoria, Australia) Measures Interferon-gamma (IFN-y) T-SPOT.TB (Oxford Immunotec Ltd, Oxford, UK) Measures peripheral blood mononuclear cells that produce IFN-γ As mentioned earlier in this presentation, we now have a blood test that can also determine whether someone has been infected with tuberculosis. These are referred to as blood assays for Mycobacterium tuberculosis (BAMTs) or T-cell interferon-gamma release assays (TIGRAs). The two commercially available products are: [review slide content] QuantiFERON-TB Gold In Tube: This test uses whole blood and measures interferon-gamma (IFN-γ) secreted from stimulated T-cells that have previously been exposed to M. tuberculosis. The QuantiFERON-TB Gold In-Tube assay is a laboratory test that involves 4 steps: Collection of blood into QuantiFERON-TB Gold In-Tube Blood Collection Tubes Overnight incubation at 37oC. TB infected patients' blood cells will produce IFN-γ. Detection of released IFN-γ in harvested plasma using an ELISA Analysis of data using the QuantiFERON-TB Gold In-Tube Analysis Software T-SPOT.TB: This is also a laboratory test. Steps involved: A peripheral blood sample is collected The white blood cells are separated out, washed and counted, then added to wells of a standard 96-well microtitre plate This plate is then incubated in the presence of antigen from the disease of interest (in this case, TB). If those antigens are present, the T cells will recognize the antigen and secrete cytokine (e.g. IFN-γ) as part of the normal immune response. This cytokine is captured by particular cytokine-specific antibodies lining the well floor. The cytokine-bound antibodies are subsequently visually illuminated using a ‘sandwich capture’ technique. This produces spots on the well floor, where each spot represents the footprint of one T cell that responded to the antigens These spots are then counted and the frequency of T cells can then be quantified

63 QuantiFERON-TB Gold In-Tube assay (Cellestis Ltd, Australia)
The QuantiFERON-TB Gold In-Tube assay (QFT-GIT), which has replaced the QuantiFERON-TB Gold assay, detects the level of IFN-γ produced in response to the M. tuberculosis antigens ESAT-6, CFP-10, and TB7.7, and uses the enzyme-linked immunosorbent assay (ELISA) detection method. This is an indirect measure of the presence of M.tuberculosis specific T-cells.

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65 T-SPOT.TB assay (Oxford Immunotec, UK)
The T-SPOT.TB measures the number of IFN-γ producing T-cells in response to the M. tuberculosis antigens ESAT- 6 and CFP-10, and is based on the enzyme-linked immunosorbent spot (ELISPOT) assay.

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72 CHARACTERISTICS OF THREE TESTS FOR LTBI
TST QFT-GOLD InTube T-Spot.TB Administration In vivo (intradermal) Ex vivo ELISA-based Ex-vivo Elispot based Antigens PPD-S or RT-23 ESAT-6 + CFP-10 +/- TB 7.7 Standardized Mostly Yes Units of measurement Millimetres of induration International units of IFN-G IFN-G spot-forming cells(SFC) Definition of positive test 5,10,15 mm Patient’s IFN-G>0.35 suIU/ml (after subtracting IFN-G response in nil control) >6 SFC in the antigen wells,with 250,000 cells/well and atleast double negative well Inderminate If anergy (rarely tested ) Poor response to mitogen (<0.5 IU/ml in positive control) or high background response (>8.0 IU/ml in nil well) Poor response to mitogen (<20 SFC in positive control well) or high background (>10 SFC in negative well) Time to result 48-72 hrs 16-24 hrs (but longer if run in batches) Cost per test $12.73 $41 $85

73 COMPARISION OF TST AND IGRAs
Estimated sensitivity in patients with active TB 75-90% 75-95% Estimated specificity in healthy individuals with no known TB disease or exposure 70-95% 90-100% Cross reactivity with BCG Yes Less likely Cross reactivity with NTM Less likely but limited evidence Association between test-positivity and subsequent risk of active TB during follow- up Moderate to strong positive association Insufficient evidence Correlation with Mycobacterium tuberculosis exposure Yes(better than TST) Benefits of treating test-positives based on RCTs No evidence Reliability and reproducibility Moderate and variable Limited evidence but appears high Boosting phenomenom No Potential for conversions and reversions Adverse reactions Rare Material costs Low High Patient visits Two One Laboratory infrastructure required yes Time to obtain results 2 to 3 days 1 to 2 days Trained personnel required

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