Mycobacterium tuberculosis complex PCR

Which test do we use?

For pulmonary specimens, CSF, and extra-pulmonary specimens with strong suspicion of rifampicine-resistant TB: Xpert MTB/RIF.

• The World Health Organization recommends the test as a primary diagnostic tool for (i) all cases suspected of multi-drug resistant TB, (ii) all HIV-positive cases suspected for TB and (iii) all cases suspected of TB meningitis (WHO/HTM/TB/2013.16),
• At ITM the test has been validated for pulmonary specimens.

For extra-pulmonary specimens other than CSF without suspicion of rifampicin-resistant TB: DNA extraction followed by in-house PCR based on the gene coding for 16S rRNA with primers specific for the genus Mycobacterium and primers specific for M. tuberculosis-complex.

• Non-tuberculous mycobacteria (NTM) are identified to the species level by sequencing of the positive ‘Mycobacterium’ amplicron.

In case of suspicion for M. lepae or M. ulcerans infection: specific in-house (q)PCR.

Sampling instructions

Possible on sputum, broncial lavage, bronchial aspirate, cerebrospinal fluid, biopsy, purulence, gastric fluid, urine, sperm, aspirates.

A minimum volume of 1 ml is required.

PCR analyses are not performed on formamide-treated samples.

Storage conditions

The samples must be kept in the refrigerator at 2-8°C.
The samples can be sent at room temperature.

Samples can be stored and shipped without additives, or in the presence of sterile physiological water.

Important advice

Attention: Xpert MTB/RIF does not allow for detection of non-tuberculous mycobacteria (NTM): analysis for such cases should be mentioned explicitly on the request form to intiiate the in-house PCR. Standard Xpert MTB/RIF analysis leaves insufficient sample to perform additional analyses.

Suspicion of M. leprae or M. ulcerans should be mentioned explicitly on the request form.

Detection limit:

• Xpert MTB/RIF: 131 CFU/ml (spiked sputum studies) or 10-100 CFU/mL(concentrated specimens)
• in-house PCR: 100 bacilli/20µl sample.

Please indicate whether art. 24bis is applicable.

If this analysis is not conform the above requirements, it will only be performed if sufficiently motivated.

If you also request a culture, the samples should not be older than 7 days.

Additional culture can only be realized if sufficient sample has been provided.