One-fifth of all TB is extra-pulmonary TB (EPTB). "Unless doctors send samples of wherever they think EPTB is, microbiologists cannot really help - pathologists cannot help. No one technology is sensitive enough for EPTB so we have to use all what we have. If everything fails then we need to start anti-TB therapy and hope for a positive clinical response" said Dr Pai.
"At times gynaecologists send wrong samples for presumptive cases of genital TB, such as menstrual blood. Blood is not a sample for TB. Unless someone is seriously septic it is not possible to detect TB in a blood sample. We need to send tissue from site of the presumptive EPTB" emphasized Dr Pai.
Gene Xpert works well to diagnose EPTB in lymph node with 83% sensitivity and TB meningitis with 80% sensitivity. "But samples have to be good quality and from site of suspected EPTB: for lymph node TB, sample should be a tissue from lymph node, and for TB meningitis, cerebro-spinal fluid (CSF) is the right sample. TB meningitis is a medical emergency - if we suspect it then the child has to be put on anti-TB therapy right then - we cannot wait for confirmatory TB tests. Gene Xpert provides 80% sensitivity for TB meningitis with CSF as sample -- highest sensitivity anyone has ever seen for TB meningitis!". Gene Xpert does not work on some samples to diagnose EPTB such as of pleural fluid. A study done by Dr SK Sharma of All India Institute of Medical Sciences (AIIMS) re-validates these findings.
Fully utilize liquid cultures!
"Liquid culture is the gold standard and most sensitive test we have which 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 TB and EPTB. Two weeks is the usual turnaround time for test results. Despite decent availability of liquid culture systems across the country in private and public health sector, these tests are significantly underused in India" said Dr Pai.
Line Probe Assays (LPAs) have 98% sensitivity and 99% specificity for rifampicin resistance, Isoniazid (INH) sensitivity always tends to be lower 84% and specificity is 99%. LPAs are also widely available in DST laboratories across the country.
Everyone deserves to be treated with drugs that work!
Universal DST is a component of the WHO's post-2015 End TB Strategy. "Everybody deserves a DST. In cities like Mumbai, one-in-five new TB cases are of MDR-TB. So we have to do DST right in the beginning. Noted TB expert Dr Zarir Udwadia had pointed out that it just takes one or two prescription errors to convert regular TB into MDR or MDR into XDR or XDR to further serious drug-resistant forms. We have to get DST done upfront and figure out the right combination of drugs sensitive for a particular patient" said Dr Pai.