Turnaround Times
Turnaround times for cultures are dependent on receipt of a pure culture containing sufficient Mycobacteria for analysis.
The time interval between receipt of a culture and the issue of the final identification and first line sensitivity report varies greatly from 1-12 weeks, depending on factors such as the nature of the culture medium used by the sending laboratory, paucity of organisms in the culture, the species of Mycobacteria and the presence or absence of contamination.
Molecular Detection of Mycobacteria in Clinical Specimens
Note on rapid molecular tests: false negatives and false positives can and rarely do occur.
We currently use Xpert MTB/RIF Ultra (Cepheid) for the direct detection of MTBC in clinical specimens and for the rapid detection of rifampicin resistance associated mutations. This is performed on a daily basis for those NHS Lothian pulmonary patient specimens fulfilling NICE based criteria and for any AFB smear positives specimens.
For detection of isoniazid mono-resistance, MDR or XDR TB, we use Xpert MTB/XDR (Cepheid). This test can be run on both primary samples and positive cultures. Please note that this test detects a limited number of common mutations associated with drug resistance. Resistance will not be detected if alternative mutations occur. This test is tun by specific justification and request of a consultant in microbiology, respiratory or infectious diseases.
Reporting of Results
Policy and procedures for telephoned results
Previously unknown AFB smear positive or discrepant samples are telephoned as soon as possible, usually within 1 working day of receipt. New positive MTB complex cultures obtained from smear negative samples are also phoned as soon as possible after their presence is confirmed in the culture.
All NTM are reported and/or E-mailed. ‘New’ M.abscessus from NHS Lothian locations are telephoned in addition.
The following examples will also be telephoned or communicated urgently:
results of direct rapid molecular tests on specimens if findings are unexpected.
clinically important identification or drug susceptibility test results (e.g. primary resistance to first line drugs; acquired new resistance; unexpected mycobacterial species).
new positive cultures from sterile sites or precious samples.
Emailing of reports to secure nhs.net or nhs.scot accounts is set up already for all Scottish user laboratories. In these instances no written report is sent out. We can set this up if you have such a secure laboratory address to automatically email each time there is an updated report. Please contact Mori Robertson in the first instance if you wish to use this means of reporting.
Initial Reports on Cultures received
Confirmation as a Mycobacterium with species identification is normally reported within 14 working days of receipt of a culture. This is achieved by AFB microscopy to confirm the presence of mycobacteria and WGS or MALDI-TOF MS for identification of cultures.
Initial rapid confirmation of MTB complex is achieved earlier using a lateral-flow immunochromatographic assay.
Final Report on Cultures received
Confirmed species identification with first line MTB complex sensitivity results may take from as little as 7 days to up to 6 weeks. This is achieved using WGS with confirmation of resistance predictions performed using phenotypic DST where appropriate.
Confirmed species identification of NTM may take 7-14 days. This is achieved predominantly using MALDI-TOF MS. Phenotypic sensitivity testing if performed, is batched on a weekly basis.
M. tuberculosis complex genotyping results are reported when completed and comparisons of the genotypes of strains suspected to be clustered are reported.
Cumulative reports
Cumulative results on a patient with positive results can be produced on request. Please contact senior BMS or medical staff at SMRL.
At present only authorised Final reports on each ‘test’ are available on SCI store. Interim results are not available.