Does a negative Mantoux test exclude infection with tuberculous bacilli?

No. Although a negative Mantoux test suggests that there is no tuberculosis, the test may be negative (less than 5 mm induration) in spite of active infection with TB bacilli if the child’s immune system is not reacting to the tuberculin. Therefore, the test may be falsely negative, even though the child has tuberculosis, in:

  • Early tuberculous infection (the Mantoux skin test becomes positive only 6 weeks to 3 months after the TB infection)
  • Very young children
  • Children with severe malnutrition
  • HIV infection and AIDS
  • After measles infection (for about 6 weeks)
  • Children with severe tuberculous disease

The test may also be falsely negative if the PPD is old or inactive, or if poor technique was used in doing the test.

The Mantoux test may be falsely negative in children with severe malnutrition, HIV infection, severe tuberculosis or after measles.

New blood tests may help to differentiate between TB and BCG infections.

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