WHO Advises Against Use of Inaccurate Serology Tests for TB

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March 23, 2011

The World Health Organization (WHO) is expected to issue a statement early this year recommending against the use of poorly performing serology tests in the diagnosis of tuberculosis (TB), according to an article in the January issue of The Lancet. The serology tests, which detect antibodies in the blood developed in response to a Mycobacteria tuberculosis infection, have been shown to be unreliable in detecting the disease. They are not the same as the interferon gamma release assays (IGRAs), which are screening tests that use a blood sample to detect exposure to TB. The serology tests are currently available in many countries around the world, but in the U.S. and other industrialized countries, they are not used to diagnose TB.

In making the decision to issue a negative recommendation, the first of its kind, WHO considered the evidence from a systematic review conducted by the Special Programme for Research and Training in Tropical Diseases (TDR). TDR is a global scientific collaboration based at WHO and sponsored by the United Nations Children's Fund (UNICEF), United Nations Development Program (UNDP) and the World Bank. TDR performed an updated review last year of the scientific data from studies that evaluated the performance of the TB serology tests. The 2010 review followed earlier evaluations conducted in 2007 and 2008.

As in the prior analyses, the latest review revealed problems with these serology tests. Their performance varied widely and lacked sufficient sensitivity and specificity, according to The Lancet article. The conclusion of the current review mirrored that of the one from 2007. In that study, none of the nine different assays that were evaluated by 68 distinct research investigations performed well compared to an acid-fast smear examination, one of the currently accepted tests for presumptive TB diagnosis. In addition, it was determined that several studies conducted to evaluate these tests were poorly designed.

Many of these commercial serology tests are sold and used in emerging nations where the disease is a serious health problem, including India and countries in Africa and Southeast Asia. Some versions of the tests are performed in laboratories while others are rapid point-of-care tests. Though they are convenient and affordable, their poor performance can lead to misdiagnoses. A wrong diagnosis may mean that those infected will not get needed therapy and may result in continued spread of the disease, or that those who are not infected may be subjected to possible side-effects from unnecessary treatment. These serious consequences have led WHO to the unusual decision of recommending against use of these unreliable tests.

In developed nations such as the U.S., TB is currently diagnosed using a combination of the long-established tests, an AFB smear and culture, plus a nucleic acid amplification test, which identifies DNA from TB bacteria. Scientists have sought to improve upon these traditional tests with faster, yet reliable technology. In December 2010, WHO endorsed a new fully automated molecular-based test that detects the genetic material of TB, though this test is not yet approved for use in the U.S. (See the article Rapid Test Endorsed by WHO) As noted in The Lancet, there is potential for serology tests to fill the need for faster yet accurate tests for TB, especially in emerging nations, but the currently available versions are unacceptable and may do more harm than good.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Morris K. WHO recommends against inaccurate tuberculosis tests. The Lancet, Volume 377, Issue 9760, Pages 113 - 114. 8 January 2011. Available online at http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)60005-6/fulltext through http://www.thelancet.com. Accessed March 2011.

(January 14, 2011) TDR News Article. Commercial TB test alert: TDR research leads to an unusual warning from WHO. Available online at http://apps.who.int/tdr/svc/news-events/news/tb-test-alert through http://apps.who.int. Accessed March 2011.

(November 2010) World Health Organization. Tuberculosis Fact Sheet. Available online at http://www.who.int/mediacentre/factsheets/fs104/en/index.html through http://apps.who.int. Accessed March 2011.

Steingart KR, Henry M, Laal S, Hopewell PC, Ramsay A, et al. 2007 Commercial Serological Antibody Detection Tests for the Diagnosis of Pulmonary Tuberculosis: A Systematic Review. PLoS Med 4(6): e202. doi:10.1371/journal.pmed.0040202. Available online at http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0040202 through http://www.plosmedicine.org. Accessed March 2011.