Interfering Substances causing errors in NAAT Assay

It is common in laboratories to see specimens with the following particles which may potentially alter nucleic acid amplification test (NAAT) results:

• Food particles
• Blood
• Tobacco
• Pan
• Debris or tissue pieces

These interfering substances cause failures in Truenat assays and may have inhibitory effects on CBNAAT assays. This interferes with the accuracy of results, leading to false positive or negative tests and delayed cycle threshold values.

Hence, it is important to follow certain precautions when collecting the specimen to avoid contaminating the specimen with these substances.

In such situations, the following protocol needs to be followed:

• Reject frank blood/bloody samples; however, the presence of blood up until 30% does not interfere in Truenat assays
• For samples containing food/tobacco/tissue particles that cause interference in processing:
  • Use a fresh sample, if available
  • Use a sample after food particles or tissue pieces settle/sediment; otherwise, reject the sample

​

Figure: Blood in Sputum Sample Interferes with PCR

Resources

• Truenat MTB Pack Insert.
• Truenat MTB Rif Pack Insert.
• Laboratory Diagnosis of Tuberculosis by Sputum Microscopy, GLI Initiative