Guardant360 CDx demonstrates significant accuracy in detecting specific genetic mutations from blood samples, particularly when compared to traditional tissue testing methods for KRAS mutations. Its performance is characterized by high negative agreement and strong overall agreement.
The accuracy of Guardant360 CDx plasma testing, relative to therascreen® KRAS RGQ PCR kit tissue testing, was evaluated in an extended analysis cohort of 189 patients. Here are the key agreement metrics:
Key Accuracy Metrics for Guardant360 CDx
To understand the test's performance, it's helpful to look at three primary metrics: Positive Percent Agreement, Negative Percent Agreement, and Overall Percent Agreement.
| Metric | Agreement (95% Confidence Interval) | Explanation |
|---|---|---|
| Positive Percent Agreement | 0.71 (0.62, 0.79) | This indicates that when the tissue test found a KRAS mutation, the Guardant360 CDx plasma test also detected it 71% of the time. This is important for identifying patients who could benefit from targeted therapies. |
| Negative Percent Agreement | 1.00 (0.95, 1.00) | This means that when the tissue test did not find a KRAS mutation, the Guardant360 CDx plasma test also did not find it 100% of the time. This high agreement helps rule out the presence of the mutation, providing confidence that a negative result is truly negative. |
| Overall Percent Agreement | 0.82 (0.76, 0.87) | This metric represents the total proportion of times the Guardant360 CDx plasma test results matched the tissue test results, whether positive or negative. An 82% overall agreement indicates a strong concordance between the two testing methods. |
Understanding What These Metrics Mean
These agreement rates provide crucial insights into how well Guardant360 CDx performs as a liquid biopsy for detecting KRAS mutations.
- Positive Percent Agreement (PPA): Also known as sensitivity, a PPA of 0.71 means that for every 100 patients with a KRAS mutation identified by a tissue biopsy, Guardant360 CDx would correctly identify 71 of them. This is vital for finding candidates for specific treatments.
- Negative Percent Agreement (NPA): Often referred to as specificity, an NPA of 1.00 indicates that Guardant360 CDx is exceptionally good at confirming the absence of a KRAS mutation. If the liquid biopsy comes back negative, it's highly likely that the mutation is not present.
- Overall Percent Agreement (OPA): This provides a comprehensive view of the test's consistency with the gold standard (tissue biopsy). An 82% overall agreement suggests that Guardant360 CDx is a reliable method for determining the KRAS mutation status.
For more detailed clinical validation data, you can refer to relevant studies and publications.
