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Tuberculosis and the New TB Blood Test

excerpt from The Parents' Concise Guide to Vaccinations by Lauren Feder, M.D.

A reader asks: I'm concerned about getting my routine TB test for work. I am 14 weeks pregnant and don't want to pass on anything harmful to my baby (namely toxins like Mercury). Is the TB test safe for children and pregnant women?

I would suggest you consider the new TB blood test that requires no injection. Called the QuantiFERON TB Gold test (QFT-G), it will be the new standard amongst adults. The drawback is that currently the lab requires two tubes of blood which is more difficult to get from small children due to their smaller veins.

Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis. Known as consumption, phthisis, and white plague, it affected great numbers of children in the 19th century. As the standards in living, sanitation, and medical care have improved, the disease has decreased in severity. In the United States, TB is less prevalent than it used to be and is considered a curable disease. Around the world, though, TB infects more than a billion people, and in developing countries, TB is still the number one cause of death.

Tuberculosis Skin Test (Mantoux Test)

The TB skin test has been the main method for detecting tuberculosis. The Mantoux test injects a small amount of tuberculin (purified, protein-derivative PPD) in the skin on the forearm. Within 48-72 hours, the patient must revisit a medical professional for examination of the forearm. However, the test is not always reliable, as sometimes there are inaccurate readings. The pitfalls to the tests are the false positive and false negative results. For this reason, the tuberculin skin test is only recommended for high-risk children and adults.

Alternatives to the Standard TB Test

Some families have refused the TB skin test on several grounds. The reasons cited include a refusal to have the tuberculin bacteria injected into the body, reports that the skin test is totally inaccurate and can lead to false-positive or false-negative results, and lack of confidence in medical professionals being able to properly interpret a skin test.

As a substitute for the skin test, there are several alternatives to test for TB. According to recent guidelines published by the CDC, the QuantiFERON TB Gold test (QFT-G) a simple blood test, that can be performed in all cases of which the TB skin test is indicated. Although recommendations are intended for healthcare providers, evaluation of immigrants with BCG vaccination, and contact investigations, many are interested in expanding the use of this test for children as well. According to current research the sensitivity of the test on children is still unknown. This test has the advantage of requiring only one visit to the office, instead of the traditional 2 day follow up with the skin test for a reading. The QFT-G is similar to the skin test, in that both can be used for screening but not diagnosis of severity of disease. For positive tests, further evaluations are required. I've been using this blood test extensively in the office, the lab requires 2 tubes of blood which is easier to get on older children.

In addition, there is a sputum AFB test for tuberculosis has been accepted by schools and in the workplace. The sputum test is performed by coughing up mucous from the lungs. The sample is sent the laboratory to rule out tuberculosis. The sputum test may not be entirely accurate either.

Tuberculosis Vaccine

The tuberculosis vaccine is the BCG (Bacille Calmette-Guérin) and it is not given in the United States. There have been questions regarding its effectiveness. Side effects include local pain, swollen glands, discharging ulcer, abscesses, tuberculosis, and a number of deaths. Following the vaccine, a person will have a positive TB test for a while. A positive reaction on a skin test after someone has recently had the BCG vaccine is not considered reliable.

Read the complete chapter in The Parents' Concise Guide to Vaccinations by Lauren Feder, M.D.

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