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TB (Tuberculosis) Mantoux Testing

This page was reviewed or revised on Friday, September 30, 2011 10:54 AM

Environmental Health & Prevention Services

What is Tuberculosis?

• A bacterial disease which causes infection, usually in the lungs but occasionally in other body organs.
• Transmitted by inhaling bacteria coughed or sneezed into the air by infected persons.

What is a TB or Mantoux test?

• The standard method used to identify people who may be infected with the TB bacteria.
• A small amount of a harmless substance called Tuberculin is injected under the skin on the forearm.

How is this read?

• In 48 to 72 hours the forearm is examined.
• An induration (firm raised area) that measures 10 millimetres or more is considered a positive test. It indicates that the person has probably had contact with tuberculosis at some point in their life.
• No reaction, or slight redness, swelling or bruising is considered a negative test. It indicates that the person has not been in contact with tuberculosis.
• If the test is positive a chest x-ray is required to rule out active disease.
• A person with a positive TB test will always have a positive test; therefore, repeat skin testing is not recommended.

Who should have a TB or Mantoux test?

• All close contacts of a person with active tuberculosis should be tested as soon as possible and again in three months.
• Employees of institutions where there is an increased risk of TB, i.e. health care facilities, homeless shelters, correctional institutions.
• TB tests may be required for new employees, volunteers, residents, or clients of some other organizations and institutions.

What is a two-step TB or Mantoux test?

• Occasionally a person’s body may not recognize the Tuberculin substance injected under the skin, even though the person was exposed to the bacteria, because the exposure was too long ago.
• Repeating the test one to three weeks following the first test can help the body to recognize the Tuberculin giving a more accurate reading.

Who should have a two-step test?

• Employees and volunteers where there is an increased risk of TB exposure and where TB testing is repeated on a regular schedule.
• Travellers who are planning to have prolonged visits in areas where there is a high risk of TB.
• Persons at increased risk of TB infections (latent TB) becoming TB disease (active TB) because of an illness or treatment.

Who should NOT have a TB or Mantoux test?

• Persons with a documented previous positive reaction.
• Persons with active TB.
• Persons who have had major viral infections such as influenza, measles or mumps in the past month should defer testing for four to six weeks.
• Persons who have been recently immunized for measles, mumps, rubella (MMR), or chickenpox (varicella) should wait four to six weeks to be tested.

Note: You can safely have a TB test if you are pregnant or breastfeeding.

Severe reactions are rare. However, you should wait 15 minutes after your injection before leaving.

Report any severe reaction to your health care provider or to Community Health Services Department.