Final answer:
Useful tests for a nodule include a biopsy, which is crucial for investigating suspected cancers, and X-rays or CT scans for detailed imaging. Blood tests and specific cultures or assays might be needed for infectious causes.
Step-by-step explanation:
When investigating a nodule, the most useful tests to consider would depend on the clinical context, but they usually include a biopsy, which is the extraction of a sample of tissue for examination under a microscope. This is particularly important in cases of suspected skin or internal organ cancer. Other tests that may be considered are X-rays or advanced imaging techniques such as CT scans, which can provide detailed images of the nodule and surrounding regions. In certain conditions, blood tests can offer critical information, and specific tests like cultures, sensitivity assays, or antibody detection might be warranted if an infectious cause is considered.