Private physicians have to suspect EPTB to start with. Then sending the right sample from the suspected site of involvement for confirmed diagnosis is no less important. "I cannot emphasize more how critical is to take the right sample from the site of involvement of presumptive EPTB. The myth in India is that EPTB can be magically picked up by peripheral venous blood. Nobody in the world has come up with a biomarker that magically tells you where EPTB is in the body. There is no role for any blood test for diagnosing EPTB [or pulmonary TB]. We have to put a needle or other appropriate methods to collect right sample from site of the disease, get a tissue or aspirate from this site and send that for microbiological confirmation. So smear sputum examination should be done in presumptive EPTB cases although without much hope but nucleic acid-amplification test (NAAT) or Gene Xpert should definitely be done with right samples. Cultures are extremely helpful in EPTB and it is worth waiting for extra two weeks [if choice of test is liquid culture] as it adds value. Histopathology is very helpful too if a trained pathologist is available," said Dr Pai.
Gene Xpert is also the preferred recommended TB test for presumptive TB meningitis because for the need of rapid diagnosis. "Within 90 minutes we get to know whether TB meningitis diagnosis is right or not. As we know TB meningitis is a medical emergency and there is no time to waste. Gene Xpert has a sensitivity of 81% and specificity of 98% for samples of cerebrospinal fluid," said Dr Pai.
WHO has reviewed the evidence of using Gene Xpert in diagnosing childhood TB. "It seems that Gene Xpert works fairly well in gastric-juice aspirates samples. Paediatric TB is officially included in WHO Gene Xpert policy," informed Dr Pai.
WHO also recommends Gene Xpert as an initial test for diagnosing TB of the lymph nodes and some other tissues too. "For diagnosing TB of the lymph nodes, sensitivity of Gene Xpert is 83% and specificity is 94%. Pleural fluid is one specimen in which Gene Xpert unfortunately does not pick up TB a lot. Pleural biopsy could add value to confirm TB," said Dr Pai.
LIQUID CULTURE
Liquid culture is the gold standard and most sensitive test we have that will not only diagnose TB but also pick up anti-TB drug resistance. "This is the only technology we have that can assay all anti-TB drugs that are critically important. It is an ideal test for smear negative and EPTB. Two weeks is the usual turnaround time, which is the only real negative factor, and is now much more affordable than in the past," said Dr Pai.
"Drug-resistance testing is critical. ISTC says that anyone who has been previously treated for TB or anyone who is not responding to standard TB treatment must receive drug-susceptibility testing (DST). Solid culture, which unfortunately has a long turnaround time of 2-3 months and is often too late for the patient, is widely available in India and is a reliable option for DST too. Liquid cultures are significantly underused in India. If we look at the number of liquid cultures done in private sector in India then we realize how underutilized this good test is. Liquid culture is the only technology we have that can generally give us a complete anti-TB drug-susceptibility profile without which we really cannot treat drug resistant TB," said Dr Pai.
LINE PROBE ASSAYS (LPAs)
Line Probe Assays are excellent rapid molecular tests that WHO approved in 2008. "LPAs have 98% sensitivity and 99% specificity for rifampicin resistance; Isoniazid (INH) sensitivity always tends to be lower, 84%, and specificity is 99%. If LPA is positive for TB and rifampicin resistance then one can confidently begin MDR-TB treatment while waiting for culture and DST reports to come [and modify treatment if required]," said Dr Pai.
"We know that INH mono-resistance is a problem in India but by and large if rifampicin resistance test is positive then clinicians should accept it as a [surrogate] marker for MDR-TB and begin treatment BUT wait for culture reports and DST to come back and modify the treatment if required," cautioned Dr Pai.
Dr Pai summarized: "No molecular test is an end in itself. Molecular tests are the start point and one has to wait for culture reports and DST to come back and finally decide what the right regimen is for a particular patient."
DO NOT USE BLOOD SEROLOGICAL TEST OR IGRAs FOR DIAGNOSING ACTIVE TB DISEASE
Immunological blood tests are not confirmatory test for active TB disease. Similarly Mantoux Skin Test is not a confirmatory test for active TB disease. Likewise IGRAs (such as Quantiferon Gold or Platinum) is also not a confirmatory test for active TB disease. Mantoux Skin Test or IGRAs are tests only for LATENT TB infection. "In children Mantoux Skin Test or IGRAs could be helpful as an indication for TB along with chest x-rays, symptoms and history of contact. WHO has recommended against using immunological blood tests and IGRAs and same has been done by RNTCP," said Dr Pai.
TREATMENT, ADHERENCE, CURE, SOCIAL SECURITY AND SUPPORT
Dr Pai emphasized that accurate diagnosis of TB is as important as providing standard treatment and care to every person with TB. With RNTCP aspiring to achieve universal access to TB care and global thrust to find, treat and cure every patient of TB as per the International Standards for TB Care (ISTC 2014), it is undoubtedly important to do every step right: diagnose TB early and accurately, provide standard anti-TB treatment without delay, help achieve cure and help those in need access social security benefits.
Bobby Ramakant, Citizen News Service -- CNS
- Shared under Creative Commons (CC) Attribution License
Gene Xpert is also the preferred recommended TB test for presumptive TB meningitis because for the need of rapid diagnosis. "Within 90 minutes we get to know whether TB meningitis diagnosis is right or not. As we know TB meningitis is a medical emergency and there is no time to waste. Gene Xpert has a sensitivity of 81% and specificity of 98% for samples of cerebrospinal fluid," said Dr Pai.
WHO has reviewed the evidence of using Gene Xpert in diagnosing childhood TB. "It seems that Gene Xpert works fairly well in gastric-juice aspirates samples. Paediatric TB is officially included in WHO Gene Xpert policy," informed Dr Pai.
WHO also recommends Gene Xpert as an initial test for diagnosing TB of the lymph nodes and some other tissues too. "For diagnosing TB of the lymph nodes, sensitivity of Gene Xpert is 83% and specificity is 94%. Pleural fluid is one specimen in which Gene Xpert unfortunately does not pick up TB a lot. Pleural biopsy could add value to confirm TB," said Dr Pai.
Liquid culture is the gold standard and most sensitive test we have that will not only diagnose TB but also pick up anti-TB drug resistance. "This is the only technology we have that can assay all anti-TB drugs that are critically important. It is an ideal test for smear negative and EPTB. Two weeks is the usual turnaround time, which is the only real negative factor, and is now much more affordable than in the past," said Dr Pai.
"Drug-resistance testing is critical. ISTC says that anyone who has been previously treated for TB or anyone who is not responding to standard TB treatment must receive drug-susceptibility testing (DST). Solid culture, which unfortunately has a long turnaround time of 2-3 months and is often too late for the patient, is widely available in India and is a reliable option for DST too. Liquid cultures are significantly underused in India. If we look at the number of liquid cultures done in private sector in India then we realize how underutilized this good test is. Liquid culture is the only technology we have that can generally give us a complete anti-TB drug-susceptibility profile without which we really cannot treat drug resistant TB," said Dr Pai.
LINE PROBE ASSAYS (LPAs)
Line Probe Assays are excellent rapid molecular tests that WHO approved in 2008. "LPAs have 98% sensitivity and 99% specificity for rifampicin resistance; Isoniazid (INH) sensitivity always tends to be lower, 84%, and specificity is 99%. If LPA is positive for TB and rifampicin resistance then one can confidently begin MDR-TB treatment while waiting for culture and DST reports to come [and modify treatment if required]," said Dr Pai.
"We know that INH mono-resistance is a problem in India but by and large if rifampicin resistance test is positive then clinicians should accept it as a [surrogate] marker for MDR-TB and begin treatment BUT wait for culture reports and DST to come back and modify the treatment if required," cautioned Dr Pai.
Dr Pai summarized: "No molecular test is an end in itself. Molecular tests are the start point and one has to wait for culture reports and DST to come back and finally decide what the right regimen is for a particular patient."
DO NOT USE BLOOD SEROLOGICAL TEST OR IGRAs FOR DIAGNOSING ACTIVE TB DISEASE
Immunological blood tests are not confirmatory test for active TB disease. Similarly Mantoux Skin Test is not a confirmatory test for active TB disease. Likewise IGRAs (such as Quantiferon Gold or Platinum) is also not a confirmatory test for active TB disease. Mantoux Skin Test or IGRAs are tests only for LATENT TB infection. "In children Mantoux Skin Test or IGRAs could be helpful as an indication for TB along with chest x-rays, symptoms and history of contact. WHO has recommended against using immunological blood tests and IGRAs and same has been done by RNTCP," said Dr Pai.
TREATMENT, ADHERENCE, CURE, SOCIAL SECURITY AND SUPPORT
Dr Pai emphasized that accurate diagnosis of TB is as important as providing standard treatment and care to every person with TB. With RNTCP aspiring to achieve universal access to TB care and global thrust to find, treat and cure every patient of TB as per the International Standards for TB Care (ISTC 2014), it is undoubtedly important to do every step right: diagnose TB early and accurately, provide standard anti-TB treatment without delay, help achieve cure and help those in need access social security benefits.
Bobby Ramakant, Citizen News Service -- CNS
- Shared under Creative Commons (CC) Attribution License
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