PGI doctor makes easy TB test available for rural India
A PGI doctor has modified a cost-effective, convenient to use TB test and made it available for rural India.
Dr Kusum Sharma at the department of microbiology, PGI Chandigarh has modified a test for extrapulmonary tuberculosis (EPTB), known as loop-mediated isothermal amplification (LAMP) test, that can be carried out without electricity in rural and low resource centres, at a low cost.
India accounts for one-fourth of the world’s estimated 10.4 million new TB cases per year and nearly a third of the 1.7 million annual TB deaths. Although extrapulmonary TB accounts for 15-20% of the pulmonary TB, for a country like India, these numbers are quite significant. Most common presentation of neurotuberculosis in the Indian subcontinent is tuberculous meningitis (TBM). Early and rapid diagnosis is crucial for successful disease management as neurological sequelae in 20-25% is due to delay in diagnosis. Most of the existing TB tests like real-time PCR is beneficial but requires expensive equipment and expertise, limiting its use to highly sophisticated facilities.
LAMP (loop-mediated isothermal amplification ) is a highly sensitive and specific TB test. The reaction takes only one hour and can be conducted under isothermal conditions (ranging from 60-650C), eliminating the need for specialized equipment or expertise. Therefore this TB test can be performed even in a rural setting and specific for TB diagnosis.
PGI doctors had earlier conducted a study "Evaluation of the TB-LAMP assay for the rapid diagnosis of pulmonary tuberculosis in Northern India" which appeared in International Journal of Tuberculosis and lung diseases.
It was performed to evaluate a commercial kit-based loop-mediated isothermal amplification (TB-LAMP) assay for the diagnosis of pulmonary tuberculosis (PTB). In the study, the TB-LAMP assay showed high sensitivity and specificity with a limited requirement of testing infrastructure and was thus found to be a promising diagnostic tool for TB diagnosis in resource-poor settings.
Prof Sharma has customised the test and made it more sensitive. “Our innovation is in using two different types of genes together for TB diagnosis. If the part of the DNA of TB bug is missed by one gene, the same can be picked up by the other gene. Therefore, it increases the sensitivity and specificity of the test,” said Prof Sharma to Times of India.
Moreover, other molecular diagnostic tests like polymerase chain reaction (PCR) need costly equipment, while this modified test only uses a simple temperature-regulated water bath. This technique, in comparison to PCR, needs minimal training and can even be carried out by any literate person with simple training and instructions on how to conduct the test. Compared to the existing molecular tests, this tool takes 90 minutes to diagnose TB and it takes 6-7 hours for a diagnosis by using the PCR test techniques.
How does the technique work? It needs patients’ sample from where the DNA is extracted. To detect the presence of the TB DNA in this sample, some reagents are added and for an hour the tubes are placed in a hot water tub. When a dye is added to the tubes, colour changes to yellow and this confirms the presence of TB DNA in the sample.
“So, all it needs is a water bath which may or even be a battery-operated tub. The cost is less than Rs 100, while the PCR test costs Rs 500-600 and takes 6-7 hours for a confirmed diagnosis,” said Prof Sharma.
“We do smear test, culture and do a couple of molecular tests. However, as TB meningitis is an emergency and needs rapid and early diagnostics, this test is handy,” she added. Developing this modification took 4-5 work years and is ongoing. “The work is at the stage of evaluation and has been tested on patients. We have evaluated on various samples of more than 500 patients suffering with ocular (eye) TB, TB of the joints and TB meningitis etc,” said Prof Sharma.
Moreover, other molecular diagnostic tests like polymerase chain reaction (PCR) need costly equipment, while this modified test only uses a simple temperature-regulated water bath. This technique, in comparison to PCR, needs minimal training and can even be carried out by any literate person with simple training and instructions on how to conduct the test. Compared to the existing molecular tests, this tool takes 90 minutes to diagnose TB and it takes 6-7 hours for a diagnosis by using the PCR test techniques.
How does the technique work? It needs patients’ sample from where the DNA is extracted. To detect the presence of the TB DNA in this sample, some reagents are added and for an hour the tubes are placed in a hot water tub. When a dye is added to the tubes, colour changes to yellow and this confirms the presence of TB DNA in the sample.
“So, all it needs is a water bath which may or even be a battery-operated tub. The cost is less than Rs 100, while the PCR test costs Rs 500-600 and takes 6-7 hours for a confirmed diagnosis,” said Prof Sharma.
“We do smear test, culture and do a couple of molecular tests. However, as TB meningitis is an emergency and needs rapid and early diagnostics, this test is handy,” she added. Developing this modification took 4-5 work years and is ongoing. “The work is at the stage of evaluation and has been tested on patients. We have evaluated on various samples of more than 500 patients suffering with ocular (eye) TB, TB of the joints and TB meningitis etc,” said Prof Sharma.
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