TB Screening Tests

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Also known as: Purified Protein Derivative; PPD; Mantoux; Latent Tuberculosis Infection Test; Interferon-gamma Release Assays; IGRA; T-Spot®.TB; QuantiFERON®-TB Gold (QFT-G); QuantiFERON®-TB Gold In-Tube (QFT-GIT)
Formal name: Tuberculin Skin Test; Interferon Gamma Release Assays

At a Glance

Why Get Tested?

To help determine whether or not you may have a latent or active infection with the Mycobacterium tuberculosis bacteria

When to Get Tested?

When you have signs and symptoms consistent with tuberculosis (TB); when you have been in close contact with someone who is known or suspected to have TB; when you have diseases or conditions that weaken your immune system and put you at a greater risk of developing active TB; when you are confined in living conditions such as a nursing home, school, homeless shelter, migrant farm camp, or correctional facility; when you inject illegal drugs; when you have lived for a period of time in or come from a foreign country where TB is more common; when you have an occupation, such as health care worker, that will bring you into close contact with those who may have active TB; sometimes as part of an examination prior to starting school or a new job (such as a college student, teacher, or day-care employee)

Sample Required?

For a tuberculin skin test, no sample is required. A small amount of purified protein derivative (PPD) solution is injected just under the first layer of skin of your inner forearm. For an interferon gamma release assay, a blood sample is drawn by needle from a vein in the arm.

Test Preparation Needed?

None

The Test Sample

What is being tested?

Tuberculosis (TB) screening tests help to determine whether a person has become infected with Mycobacterium tuberculosis bacteria, the cause of TB. The screening tests measure the body's immune response to antigens derived from the bacteria – either directly as a skin reaction to a tuberculin skin test (TST) or indirectly with an interferon gamma release assay (IGRA) blood test.

TB, once called consumption, has been recognized as causing illness for thousands of years. This bacterial infection may affect many body organs, but it primarily targets the lungs. TB may cause an inactive (latent) infection or an active, progressive disease. The immune system of about 90% of the people who become infected with TB manage to control its growth and confine the TB infection to a few cells in the body. The bacteria in these cells are inactive but still alive. The person does not have any symptoms and they are not infectious, but they do have a "latent TB infection." If, after some time, the person's immune system becomes weakened (compromised), the mycobacteria may begin to grow again, leading to an active case of tuberculosis disease. Active TB does cause illness in the person and it can be passed to others through respiratory secretions such as sputum or aerosols released by coughing, sneezing, laughing, talking, singing or breathing.

The tuberculin skin test involves two steps: the injection of a small amount of purified protein derivative (PPD) solution under the first layer of skin of the forearm and an evaluation of the injection site conducted by a health care worker at 48 and/or 72 hours to see if a local skin reaction has occurred. The IGRA test measures the release of gamma interferon by white blood cells in a sample of blood when the cells are exposed to specific TB antigens. Both tests can detect M. tuberculosis infections, but neither can distinguish between latent and active infections.

Photo of TB skin test

How is the sample collected for testing?

For the tuberculin skin test, no sample is required. The test is performed on a person's skin. A purified protein derivative (PPD) solution that contains M. tuberculosis antigens, but not live bacteria, is used to provoke a hypersensitivity skin reaction (a red raised bump) in those who have been infected by TB.

A health care worker will wipe the inner forearm with alcohol and let the skin dry. Using a 1cc syringe and a tiny needle, he will inject a small amount of PPD solution just under the first layer of the skin. When done correctly, the injection forms a small bubble of fluid that looks like a blister. The site should be left uncovered and undisturbed. The site must be examined by a health care worker at 48 and/or 72 hours to see if a local skin reaction has occurred.

For an interferon gamma release assay, a blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. 

The Test

Common Questions

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Article Sources

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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.

Sources Used in Current Review

(Updated 2009 June 1). Testing & Diagnosis, Testing for TB Infection. CDC Tuberculosis (TB) [On-line information]. Available online at http://www.cdc.gov/tb/topic/testing/default.htm through http://www.cdc.gov. Accessed June 2010.

Zhao, X. et. al. (2009 November 30). Is the QuantiFERON-TB Blood Assay a Good Replacement for the Tuberculin Skin Test in Tuberculosis Screening? A Pilot Study at Berkshire Medical Center. Medscape from American Journal of Clinical Pathology. 2009;132(5):678-686. [On-line information]. Available online at http://www.medscape.com/viewarticle/712651 through http://www.medscape.com. Accessed June 2010.

Herchline, T. et. al. (2010 June 9). Tuberculosis. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/230802-overview through http://emedicine.medscape.com. Accessed June 2010.

(Reviewed 2009 June 1). QuantiFERON®-TB Gold Test, CDC Tuberculosis (TB) Fact Sheet [On-line information]. Available online at http://www.cdc.gov/tb/publications/factsheets/testing/QFT.htm through http://www.cdc.gov. Accessed June 2010.

(2009 October 1). CDC Immigration Requirements: Technical Instructions for Tuberculosis Screening and Treatment, CDC [On-line information]. PDF available for download at http://www.cdc.gov/immigrantrefugeehealth/pdf/tuberculosis-ti-2009.pdf through http://www.cdc.gov. Accessed June 2010.

(Reviewed 2009 June 1). Tuberculin Skin Testing. CDC, Tuberculosis (TB) Fact Sheet [On-line information]. Available online at http://www.cdc.gov/tb/publications/factsheets/testing/skintesting.htm through http://www.cdc.gov. Accessed June 2010.

Madariaga, M. et. al. (2007 November 16). Clinical Utility of Interferon Gamma Assay in the Diagnosis of Tuberculosis Medscape from J Am Board Fam Med. 2007;20(6):540-547 [On-line information]. Available online at http://www.medscape.com/viewarticle/565794 through http://www.medscape.com. Accessed June 2010.

Mazurek, G. et. al. (2010 June 25). Updated Guidelines for Using Interferon Gamma Release Assays to Detect Mycobacterium tuberculosis Infection — United States, 2010. CDC, Morbidity and Mortality Weekly Report (MMWR) June 25, 2010 / Vol. 59 / No. RR–5 [On-line information]. Available online at http://www.cdc.gov/mmwr/ through http://www.cdc.gov. Accessed June 2010.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 953-954.

(July 2010) Centers for Disease Control and Prevention. Tuberculosis, Testing for TB, Pregnancy. Available online at http://www.cdc.gov/tb/topic/populations/pregnancy/default.htm through http://www.cdc.gov. Accessed March 2010.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Heimerdinger, M. (2000). Tuberculosis. ACP-ASIM [On-line session report]. Available online at http://www.acponline.org/vas2000/sessions/tb.htm through http://www.acponline.org

Kirchner, J. (2000 February 1). Do Sputum Smears Positive for AFB Signify Treatment Failure? American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20000201/tips/25.html through http://www.aafp.org.

Jerant, A. et.al. (2000 May 1). Identification and Management of Tuberculosis. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20000501/2667.html through http://www.aafp.org.

Sadovsky, R. (2001 May 15). Making the Diagnosis of Tuberculosis in Children. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20010515/tips/9.html through http://www.aafp.org.

Centers for Disease Control and Prevention (CDC) (2002 August 13, Reviewed). Frequently Asked Questions, Questions and Answers about TB. National Center for HIV, STD and TB Prevention Division of Tuberculosis Elimination [On-line information]. Available online at http://www.cdc.gov/nchstp/tb/faqs/qa.htm through http://www.cdc.gov.

Tuberculosis. The Merck Manual of Medical Information--Home Edition [On-line information]. Available online at http://www.merck.com/pubs/mmanual_home/sec17/181.htm through http://www.merck.com.

Tan, L.J. (2000 June 28, Updated). ATS/CDC Statement Revises Treatment and Testing for Latent TB Infection. American Medical Association [On-line information]. Available online at http://www.ama-assn.org/ama/pub/article/1865-2125.html through http://www.ama-assn.org.

Mazurek, G. & Villarino, M. (2002 December 18 Updated). Guidelines for Using the QuantiFERON®-TB Test for Diagnosing Latent Mycobacterium tuberculosis Infection. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report [On-line report]. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/di51cha1.htm through http://www.cdc.gov.

Centers for Disease Control and Prevention (2002 March 23, Reviewed). TB and HIV Coinfection. National Center for HIV, STD and TB Prevention, Division of Tuberculosis Elimination [On-line information]. Available online at http://www.cdc.gov/nchstp/tb/pubs/TB_HIVcoinfection/default.htm through http://www.cdc.gov.

Tuberculosis: Ancient Enemy Present Threat, "I must die": Tuberculosis in History. NAIAD [On-line information]. Available online at http://www.niaid.nih.gov/newsroom/focuson/tb02/story.htm through http://www.niaid.nih.gov.

Tuberculosis (TB). American Lung Association [On-line information]. Available online at http://www.lungusa.org/diseases/lungtb.html through http://www.lungusa.org.

(2002 January). American Lung Association® Fact Sheet: Tuberculosis. ALA [On-line information]. Available online at http://www.lungusa.org/diseases/tbfac.html through http://www.lungusa.org.

(2002 January). American Lung Association® Fact Sheet: Tuberculosis Skin Test. ALA [On-line information]. Available online at http://www.lungusa.org/diseases/tbskinfac.html through http://www.lungusa.org.

(2002 January). American Lung Association® Fact Sheet: Pediatric Tuberculosis. ALA [On-line information]. Available online at http://www.lungusa.org/diseases/pedtbfac.html through http://www.lungusa.org.

NIAID (1999 December 1, Updated). The Global Burden of Tuberculosis. National Institute of Allergy and Infectious Diseases, National Institutes of Health [On-line publication]. Available online at http://www.niaid.nih.gov/publications/blueprint/page2.htm through http://www.niaid.nih.gov.

Tuberculin skin test. Hendrick Health System AccessMed [On-line information]. Available online at http://www.hendrickhealth.org/healthy/00069330.html through http://www.hendrickhealth.org.

Tuberculosis. Hendrick Health System AccessMed [On-line information]. Available online at http://www.hendrickhealth.org/healthy/00069340.html through http://www.hendrickhealth.org.

Mycobacteriology, Introduction to the Genus Mycobacteria. Microbiology Public Health for Northern Alberta, Bugs on the Web [On-line information]. Available online at http://www2.provlab.ab.ca/bugs/mycob/mbintro.htm through http://www2.provlab.ab.ca.

Mycobacteriology, Acid-Fast Staining Procedures for Mycobacteria. Microbiology Public Health for Northern Alberta, Bugs on the Web [On-line information]. Available online at http://www2.provlab.ab.ca/bugs/mycob/afb_stain/afb_tutorial.htm through http://www2.provlab.ab.ca.

Hall, G. (2001). Practical Microbiology, Update on Broth Media for the Isolation of Mycobacterium Species. Medscape from Infect Med 18(1):28-30, 2001 [On-line journal]. Available online at http://www.medscape.com/viewarticle/410131 through http://www.medscape.com.

Tuberculin Purified Protein Derivative (Mantoux) Tubersol. Aventis Pasteur Inc. (Swiftwater, PA) [Package Insert].

(1996 October 28, Rev L). AccuProbe, Mycobacterium Tuberculosis Complex Culture Identification Test. Gen-Probe [Package Insert]. Available online at http://www.gen-probe.com/mtd.html through http://www.gen-probe.com.

(2006 March). QuantiFERON-TB Gold Test. Accessed December 10, 2006. National Center for HIV, STD, and TB Prevention, Division of Tuberculosis Elimination Fact Sheet [On-line information]. Available online at http://www.cdc.gov/nchstp/tb/pubs/tbfactsheets/250103.htm through http://www.cdc.gov.

(2006 April). Diagnosis of Tuberculosis Disease. Accessed December 10, 2006. National Center for HIV, STD, and TB Prevention, Division of Tuberculosis Elimination Fact Sheet [On-line information]. Available online at http://www.cdc.gov/nchstp/tb/pubs/tbfactsheets/250102.htm through http://www.cdc.gov.

QuantiFERON - TB Gold In-Tube: FAQs. Available online at http://www.cellestis.com/. Accessed November 2008.