CBNAAT Sample Processing for Other Body Fluids

The following procedures are recommended when processing various body fluids with the Cartridge-based Nucleic Acid Amplification Test (CBNAAT):

Bronchoalveolar Lavage (BAL): 

Processing of BAL for CBNAAT assay is given here. However, it is important that each laboratory optimizes this protocol to minimize the error rate.

If the BAL volume is sufficient (approx. 5 ml), centrifuge and dissolve sediment into 1 ml sterile phosphate buffer/ saline, then add sample reagent in a 1:2 ratio.

If the BAL volume is less (less than 5 ml), take 1 ml and add 2 ml of sample reagent.

• If the BAL is mucoid or has more than 0.5% blood contamination, decontaminate using N-acetyl-l-cysteine–sodium hydroxide (NALC-NaOH) treatment.
• Decontamination of BAL should also be carried out if the error rate is more than 2%.

Pericardial/ Ascitic/ Synovial Fluid:

If the sample volume exceeds 5 ml, centrifuge and dissolve sediment into sterile phosphate buffer/saline to make volume 1 ml, then add sample reagent in a 1:2 ratio.

If the sample volume is less than 5 ml, take 1 ml and add 2 ml of sample reagent.

• Pleural fluid is a suboptimal sample, and pleural biopsy is preferred. 
• A positive CBNAAT result in pleural/body fluid can be treated as TB, a negative result should be followed by other tests.
• Decontaminate/concentrate using standard NALC-NaOH treatment if bloody (more than 0.5% blood), thick and/or clots are present.

Pus/ Abscess/ Aspirates/ Semen:

• Liquid/ slightly viscous specimen: Use sample-to-sample reagent 1:2 ratio, mix well and follow routine CBNAAT protocol.
• If very thick, viscous or bloody specimens: Add 2 ml sample reagent to 0.2 - 0.3 ml pus, mix well to the vortex, and increase the incubation time, if required.
• Decontaminate, if required (>0.5 % blood).

*Each laboratory must optimize these protocols to minimize the error rate.

Resources

• Xpert MTB/RIF Assay for the Diagnosis of Pulmonary and Extrapulmonary TB