From the Guidelines
The negative predictive value of a Clostridioides difficile (C. diff) test is typically >99%.
Details of the Evidence
- The high negative predictive value is based on the use of highly sensitive testing strategies, such as 2-stage algorithms or stand-alone NAATs 1.
- This means that a single negative test result has a very high likelihood of accurately ruling out CDI.
- The evidence suggests that repeat testing within a 7-day period has a low diagnostic yield of approximately 2% 1.
- However, repeat testing may be considered in certain situations, such as epidemic settings or for symptomatic patients with a high clinical suspicion of CDI but a negative initial test result 1.
- It is also important to note that recurrent CDI occurs commonly, and repeat testing should be considered in patients who experience a recurrence of symptoms following successful treatment 1.
From the Research
Negative Predictive Value of C. diff Tests
The negative predictive value (NPV) of a C. diff test is a measure of the probability that a patient with a negative test result truly does not have the infection.
- The NPV of the C. DIFF QUIK CHEK COMPLETE test was found to be 91.7% 2 and 89.1% for the Quik Chek Complete CDT 3.
- The NPV of the Tox A/B EIA was found to be 85.8% 2.
- The NPV of the BD MAX Cdiff assay was found to be 100% for all patients, pediatric patients, and adult patients 4.
- The NPV of the Xpert CD assay was found to be 98.7% 3.
- The NPV of the glutamate dehydrogenase (GDH) test was found to be 99.4% 3 and 99.3% 5.
Comparison of NPV Values
The NPV values of different C. diff tests vary, with the BD MAX Cdiff assay having the highest NPV of 100%, indicating that a negative result can reliably rule out the infection.
- The C. DIFF QUIK CHEK COMPLETE test and the Xpert CD assay also have high NPV values, indicating good performance in ruling out the infection.
- The Tox A/B EIA has a lower NPV, indicating that a negative result may not always rule out the infection.
- The GDH test has a high NPV, indicating that it can be a useful screening tool for C. diff infection.