CDST_LT: MGIT Reading and reporting

Documentation of MGIT cultures is important to characterise if growth is positive for M. tuberculosis or unexpected result/contamination. The growth is tested for AFB by ZN microscopy and sterility by inoculation on the BHI agar/LJ slant. 

The documentation of growth is as follows:

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MGIT 960 User manual

Assessment

• In automated systems, tubes are read continuously and flagged when positive.  Performing acid-fast bacteria (AFB) smear with Zeihl-Neelsen (ZN) staining determines the next steps.

•  All MGIT-negative tubes at the end of the incubation period should be visually checked for evidence of growth before being discarded.

• ZN staining should be performed on growth as soon as possible. After staining, culture should be handled according to the results.

  Resource

  Mycobacterial Culture

  Assessment

Detection time can range from 24 hours to six weeks for MGIT. The pictorial representation of MGIT 960 culture detection is shown below:

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Assessment

The MGIT 960 offers a variety of reports which may be helpful in your daily workflow. Examples of these reports can be found in your binder.

The Unloaded Positives report will list all the positive tubes removed from the instrument since the last time the report was printed (up to a maximum of 500 positive, negative and ongoing tubes). This report could serve as a worksheet to document ZN stain results. It could help you account for every positive tube that was removed and ensure each was stained accordingly.

The Unloaded Negatives report will list all of the negative tubes removed from the instrument since the last time the report was printed. The same maximum tube capacity applies. This report may be helpful when reporting out-of-protocol negatives.

At times, ongoing tubes may need to be removed from the instrument to make room for newly processed tubes. (NOTE: If you need to remove ongoing tubes early, be sure to remove the oldest tubes first). The Unloaded Ongoing report can help you so that all tubes are tracked and reported appropriately. When the report printing is confirmed, the records for these unloaded tubes are removed (deleted) from the system. This is why you will be asked to confirm that the report successfully prints.

The instrument inventory report will give you a printout of all tubes in the instrument and their current status. This is a less frequently used report.

The Quality Control report lists the status of all of the detectors and the date and time of their last verification. This report also lists all manually blocked stations in the instrument. Some accounts print this report daily. This report may be useful for complying with local inspecting agencies.

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Assessment

The beauty of the MGIT 960 tubes is that they can be read by the instrument and also manually. There are times AFB cultures are incubated at temperatures other than 37^oC. If that is the case, the MGIT tube can be incubated at an alternate temperature. These tubes would then need to be read manually with a Wood’s Lamp or other UV sources of the proper wavelength and intensity.

In the event of an instrument failure where the instrument is down for an extended period, you may decide to incubate the tubes offline. These tubes can also be read manually.

Manual readings should not be conducted in a darkened room or rooms with bright sunlight. Normal room lighting is appropriate. When using any UV source, one must always wear protective UV goggles.

To read the tubes manually, place the rack of tubes directly on top of the UV lamp. There is no need to take the tubes out of the rack. Some accounts leave a blank row between tubes. This can make it easier to see the fluorescence when reading the tubes.

Tilt the tubes/rack slightly so that the tubes are read at a slight angle. Look for fluorescence both at the sensor at the bottom of the tube and the meniscus at the top of the media line (the fluorescence of the sensor reflects in the meniscus). Place a positive and negative control at the end of the row to give visual assistance in the reading. Place the suspect between these two tubes to determine if the patient tube is positive. The fluorescence in the patient tube should be greater than the background fluorescence in the negative control but does not need to be as great as the fluorescence in the positive control to be considered positive.

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Assessment