Laboratory confirmation requires at least one of the following:

• positive culture for M. tuberculosis complex
• positive microscopic examination for acid-fast bacilli when a culture has not been or cannot be obtained
• demonstration of M. tuberculosis complex nucleic acid directly from specimens**
• histology strongly suggestive of tuberculosis when there is a strong clinical probability.

Note: Positive nucleic acid tests do not show whether the organisms are viable or not and may be positive after successful treatment. They should not be used to diagnose treatment failure.

**Demonstration of M. tuberculosis nucleic acid:

• This does not include positive DNA “probe”. (This identifies nucleic acid from a mycobacterial culture and therefore by definition confirmation has already been made).
• It does include a nucleic acid amplification test (NAAT), where the clinician accepts this as presumptive evidence of TB. In body fluids positive NAATs do not show whether the organisms are dead or alive.

For instruction on diagnostic tests and management of LTBI refer to the Guidelines for Tuberculosis Control in New Zealand 2019 (Ministry of Health 2019).