Faster, Better Test for Tuberculosis

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A new, faster test can reveal if a person has tuberculosis (TB). It also can tell if the disease is resistant to antibiotics. The new test takes less than two hours. The old one could take up to a week. The old test also misses cases of TB, so sick people are mistakenly told they are healthy. In a study of 1,730 people, the new test identified 98% of TB cases. It also identified 98% of the cases that were resistant to rifampin, a common drug used to treat TB. Tuberculosis is a bacterial infection. It causes more than 1.8 million deaths each year. The new test is not the same as the skin test. The skin test is done to see if someone has ever been exposed to TB. The new test would be done in people who have TB symptoms. The study about the test appeared in the September 1 issue of the New England Journal of Medicine.

What Is the Doctor's Reaction?

Doctors have had no quick way to diagnose tuberculosis (TB) until now. A new test called Xpert MTB/RIF has just changed that. And this is not one small step. The test is a major advance in medicine.

The new TB test:

• Can diagnose someone with active disease within 90 minutes


• Is extremely accurate


• Can help design the best antibiotic treatment for someone who does have TB


• Is easy to do and can be performed by someone after a short period of training

To diagnose TB involving the lungs, doctors need to obtain a sample of mucous from deep in the lungs. If the person is not coughing up any mucous, a procedure called an induced sputum collection is performed. In an isolation room, a respiratory therapist uses non-invasive techniques to stimulate a deep cough.

Currently, the next step is sending the mucus sample to the laboratory. Some of the sample is put on a slide and the rest is sent for a TB culture. A specially trained technician carefully scans the slide to look for TB bacteria. The process is labor intensive. Even in the best hands, the TB bacteria won’t be seen more than half the time.

The TB culture is more accurate. It may turn positive in several days. But a doctor cannot definitively say the person does not have TB until the culture has had time to grow over several weeks. This usually means treating a person suspected of TB while waiting for the final report.

In less developed countries, not having an immediate diagnosis of TB means that treatment will usually be delayed. Therefore, the person not yet diagnosed can infect others. Halting the spread of TB has had some success in countries that have adopted certain strategies. A rapid TB test will greatly improve efforts to control TB.

In addition to rapid diagnosis of TB, the test can also determine whether the strain of TB is resistant to rifampin. Treatment of active TB requires a combination of antibiotics, often 3 different drugs. Rifampin is one of the drugs commonly used as part of the combination therapy. If the strain is resistant, rifampin won’t be used and treatment is more likely to be successful. This is especially important today because TB has become resistant to many antibiotics.

What Changes Can I Make Now?

Once available, this new diagnostic test for TB will actually save money on health care in the United States and other developed countries. Because TB is contagious, anyone admitted to the hospital with a possible diagnosis of TB is placed in a private room with special ventilation (“isolation”). This is always more costly than a regular room.

Before the person can be moved out of isolation, there needs to be at least one sample of mucous that is examined under a microscope of TB bacteria. Some hospitals require three negative samples prior to determining the person is not contagious.

Today, the great majority of people are put into isolation because of possible TB don’t have it. The new TB test can immediately determine if the person needs to be in an isolation room. Not only will this save money, the patient and family don’t have to worry about TB for the usual two to three days.

What Can I Expect Looking to the Future?

Although the cost of the new test is somewhat higher than other tests used to diagnose TB, the test may actually save money, potentially lots of money. More rapid and more accurate diagnosis means that:

• Money won't be spent on drugs that aren't needed (people often need treatment while waiting on final TB culture results).


• Money won’t be spent on an ineffective antibiotic if the TB strain is resistant to rifampin.


• People with TB won't be walking around untreated, so TB spread will decrease and fewer people will need TB treatment.


• Hospitals will need fewer special isolation rooms.