Medical Xpress (08.21.2013)
A new TB screening method to diagnose active TB was introduced to screen more than 20,000 people in Pakistan. The test looks for antibodies that are present in the blood of individuals fighting active TB. Currently, TB is diagnosed by examining a sputum sample under a microscope to identify the TB bacterium, which only detects approximately 50 percent of cases of active TB. The new test is expected to find almost 80 percent of cases and uses a few drops of blood. Results are available in two hours compared to the sputum test, which requires three sputum samples collected over three days. Peoples’ immune systems do not always produce the same kind of antibodies in reaction to the TB bacterium; hence, the system screens for eight to 10 key antibodies.
The new test is based on a diagnostic instrument approved by the US Food and Drug Administration and developed by the University of California Davis Medical Center in collaboration with colleagues in Pakistan. The preliminary trials funded by the US Agency for International Development (USAID) were published in the journal Clinical and Vaccine Immunology. A grant from the US State Department and USAID will be used to develop and commercialize the test in collaboration with the Forman Christian College in Pakistan.
Since children have difficulty providing sputum samples, they are often not screened. Also, an individual can have extrapulmonary TB, which is not detected with sputum screening. These two groups represent 20 percent of cases that are usually not diagnosed, but now their disease can be detected with the new test. Another technique used in some clinics is growing a culture from a sputum sample before the sample is examined. The culture test can take two months compared to the new technique that can analyze approximately 100 samples in two hours. As a result, a large number of people can be tested and begin early treatment.
The initial cost of the antibody testing machines is high, but because more people can be tested, the cost per patient is similar to that of the microscopy test. Three hospitals in different regions of Pakistan will share the machine. The machine can also test blood samples that were dried on filter paper and sent from rural clinics to a major urban hospital.
Imran Khan, assistant professor in the Department of Pathology and Laboratory Medicine and Center for Comparative Medicine at UC Davis Medical Center, and colleagues are working on a second method that screens for certain immunomodulators. Testing for antibodies and immunomodulators can improve the new strategy’s rate of TB diagnosis to 90 percent. The team is also developing a third test using the same diagnostic screening platform to detect drug-resistant TB strains.