Indications for retesting in CBNAAT

The assay needs to be repeated by using a new cartridge if one of the following test results occur:

INVALID: An INVALID result indicates that Sample Processing Control (SPC) failed. The sample was not properly processed, or Polymerase Chain Reaction (PCR) was inhibited.

ERROR: An ERROR indicates that Probe Check Control (PCC) failed, and the assay was aborted possibly due to the reaction chamber being filled improperly, a reagent probe integrity, syringe pressure issues, or failure of the CBNAAT module.

NO RESULT: A NO RESULT indicates that insufficient data were collected. For example, the operator stopped a test that was in progress.

RIF Indeterminate: RIF indeterminate result indicates that the sample has a less bacterial load.

Program guidelines recommend obtaining a second specimen to confirm rifampicin resistance in these scenarios.

How to Perform the Retest?

• Leftover sputum or fresh sputum or reconstituted sediment: 

Treat it with a new Sample Reagent (SR) and load it into the new CBNAAT cartridge.

• Sufficient leftover SR-treated sample: 

Use within 4 hours of initial addition of SR to the sample - Load into the new CBNAAT cartridge.

Do not use SR-treated sample if it is more than 4 hours old - Over-treatment may lead to false-positive test results.

Always use a new cartridge! 

Video : Retest Protocol for CBNAAT

Resources

• GeneXpert Xpress SARS-CoV-2: Instructions for Use, Cepheid Manual.