TB Blood Test, Forget TB Skin Tests

Excerpt from Child Health Guide, North Atlantic Books, Spring 2005

Tuberculosis skin tests have existed for 100 years to diagnose possible
infections. The test is presented as a benign, protective necessity.
However, TB tests may not be as benign as purported. A TB skin test, the
Mantoux (tuberculin) test or the Tine test, involves injecting a small
amount of tuberculosis antigen into the skin. A clinician will observe the
skin reaction to this test. If there is a positive reaction of swelling,
redness, or blistering then the test is pronounced positive. A positive
result means that the person has been exposed to tuberculosis bacteria at
some time in the past and developed antibodies. However, false positive and
false negative test results are common. If someone had a TB vaccination at
any time in the past, or if they were exposed to TB, then their antibodies
to the vaccine will cause a positive TB skin test. Ninety percent of people
exposed to TB will not contract the disease. The skin test fails to detect
half of people with latent TB, and false-negatives are common in
individuals with weakened immune systems. Usually anyone with a positive
skin test for TB is advised to complete at least six months of treatment
with the antibiotic isoniazid (INH). It is estimated that 50 percent of
people prescribed antibiotics on the basis of a positive skin reaction do
not have TB infection at all.

The injection of a small quantity of antigen is not supposed to cause any
systemic reaction, but it is possible that even this small amount of TB
antigen could trigger the body’s immune system to react abnormally. I have
seen autoimmune disease processes begin soon after TB tests, and others
have also reported this occurrence. This observation does not prove that a
TB test can cause this reaction, but it should give us pause before
allowing the test to be performed on children.

A much safer, more accurate, quicker, and convenient blood test exists for
the detection of tuberculosis infection. The blood test is performed on a
plasma sample with results available in 24 hours. In Europe the blood test
was approved for use in July 2004 and will replace the tuberculin skin
test. This test is approved to detect both active and latent TB in infants,
children, and adults. The test detects T cell response to infection which
can exist in the body for years without symptoms. The population of
latently infected people acts as a reservoir of TB with undetected
individuals capable of spreading infection. A similar blood test was
approved by the FDA in 2001 for detection of latent TB in the US and
recommended for individuals at high risk or for screening purposes. Some
labs do the test, but not all, so it may take some searching to find it.
The name of the test is the Quantiferon TB gold blood test.

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Written by Randall Neustaedter OMD

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