Diagnostic Testing
A diagnostic test is offered as a follow-up to a positive routine screening test to confirm the results or after symptoms lead to the suspicion of cancer. The person may choose to take the test or choose not to take the test. All individuals with a positive routine screening test are offered a colonoscopy as the default diagnostic test. The user may override the default, but the model assumes that the test has 100% specificity and that a polypectomy will be performed if the test reveals the presence of polyps. The diagnostic test has two possible side effects: immediate death and perforation. These outcomes are handled in the same way as they are for the routine screening test.
If the person has lesions:
The model checks each lesion individually to see whether the diagnostic test detects the lesion. The probability that a diagnostic test detects a lesion is controlled by the test’s sensitivity parameters, as described for the routine screening test. A positive test result occurs when the test detects at least one of the lesions, and a negative test result occurs when the test fails to detect every lesion present. Detected polyps are removed immediately via a polypectomy. If a cancerous lesion is detected, the model assumes that any other cancerous lesions are also detected. Therefore, a person’s cancer stage at initial diagnosis is always the most advanced stage of any of his or her cancerous lesions. Following the removal of at least one lesion, the individual’s screening modality will always be colonoscopy thereafter. If the individual originally screened with colonoscopy, he or she will continue to screen by colonoscopy. If the individual originally screened by a modality other than colonoscopy, his or her modality will be permanently changed to colonoscopy following polyp removal.
If the person does not have lesions:
The test will always correctly produce a negative result because the model assumes that the diagnostic test has 100% specificity. That is, the diagnostic test will never yield a false positive result.
A positive diagnostic test leads to recommended surveillance
After a positive diagnostic test result, the person is recommended to undergo surveillance. If any of the detected lesions were cancerous, the person is first eligible for cancer treatment, which may improve his or her expected survival.
A negative diagnostic test classifies a person as low-risk for some period
After a negative diagnostic test result, the person is categorized as low-risk for a period of time. This applies to all negative diagnostic test results: the person had lesions but the test did not detect the lesions; the person did not have any lesions; and a colonoscopy was administered as the routine screening test. During the time when the person is considered low-risk, he or she does not participate in routine screening tests. The duration of the low-risk period can be set independently for each population in the model.