What is a key characteristic of tests that were identified as imminent and serious threats to public health?

The key characteristic of tests identified as imminent and serious threats to public health is that they were not CLIA-waived tests. CLIA, which stands for the Clinical Laboratory Improvement Amendments, regulates laboratory testing and establishes standards for laboratory quality. CLIA-waived tests are those that are simple enough to be performed by non-laboratory personnel and are considered to pose a low risk to patients if they are performed incorrectly.

Tests that are deemed imminent and serious threats to public health typically require a higher level of oversight because they can significantly impact health outcomes. These tests often have complex methodologies and require more precise handling and interpretation of results. As such, they cannot be classified as CLIA-waived. This distinction highlights the need for more stringent regulations, training, and monitoring to ensure accurate results, which is essential when addressing serious public health concerns.

The other options do not capture the essence of what makes a test a serious threat; being expensive, qualitative only, or having been in use for many years does not inherently indicate a test's potential public health risk.