Nucleic acid amplification test (NAAT): NAATs often use the polymerase chain reaction (PCR) to identify one or more genes specific for the toxigenic strains, A and B. The test can identify the critical C diff genes tcdB that codes for toxin B, and tcdA that codes for toxin A. NAATs are rapid, highly sensitive assays that are specific for toxigenic C diff strains, however, they do not identify active toxin production. Because NAATs have high sensitivity but are unable to identify active toxins, the test is unable to separate active CDI from asymptomatic carriers. NAATs can lead to the over-diagnosis of CDI and could result in the use of antibiotics in patients not needing treatment for CDI.
NAATs have increasingly become the benchmark method to test for C diff. Although it can be used alone, it is typically used in combination with the EIA test for GDH antigen and EIA test for toxins A and B. In addition, the NAAT may be used as a confirmatory test if the EIA results are discordant.
As previously noted, it must be pointed out that exclusive reliance only on the NAAT test to diagnose CDI may lead to overdiagnosis and over-treatment. More details on the testing guidelines are presented in other sections of this course.
