A gynecologic oncology research institute isolates a potential tumor marker for endometrial cancer. A large multicenter study is then performed to evaluate serum levels of the tumor marker in women with and without endometrial cancer. The following curves are generated using the results of the study. Clinical researchers decide to use the tumor antigen to develop a confirmatory test for patients with suspected endometrial cancer. During preliminary design of the test, the cutoff point for positive/negative results is set at point A. If the cutoff point is moved from A to B, the specificity of the test will change in which of the following ways?

Question

A gynecologic oncology research institute isolates a potential tumor marker for endometrial cancer.  A large multicenter study is then performed to evaluate serum levels of the tumor marker in women with and without endometrial cancer.  The following curves are generated using the results of the study.  Clinical researchers decide to use the tumor antigen to develop a confirmatory test for patients with suspected endometrial cancer.  During preliminary design of the test, the cutoff point for positive/negative results is set at point A.  If the cutoff point is moved from A to B, the specificity of the test will change in which of the following ways?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d321_899f_bc81_419671e2f12e_MD0003_00 Important parameters of diagnostic tests include the following: True positive (TP) - A patient with a positive test result who actually has the disease. False positive (FP) - A patient with a positive test result who actually does not have the disease. True negative (TN) - A patient with a negative test result who actually does not have the disease. False negative (FN) - A patient with a negative test result who actually has the disease. Sensitivity - The number of patients correctly testing positive for a disease divided by the total number of patients with the disease (TP / [TP + FN]). High sensitivity means that negative results are less likely to be FNs and more likely to be TNs; thus, a negative result is better able to rule out the disease (SnOut). Because tests with high sensitivity will correctly identify most of the patients with the disease, sensitivity is very important for screening tests (which need to minimize FNs). Specificity - The number of patients correctly testing negative for a disease divided by the total number of patients without the disease (TN / [TN + FP]). High specificity means that positive results are less likely to be FPs and more likely to be TPs; thus, a positive result is better able to rule in the disease (SpIn). Because tests with high specificity will correctly identify most of the patients without the disease, specificity is very important for confirmatory tests (which need to minimize FPs). In this example, moving the cutoff point from A to B will cause more patients without the disease to test negative (fewer FPs), increasing the specificity of the test. However, as a consequence, more patients with the disease will also test negative (more FNs), resulting in decreased sensitivity. Conversely, moving the cutoff point in the other direction (eg, B to A) will increase the number of FPs and decrease the number of FNs, decreasing specificity while increasing sensitivity. Educational objective: Changing the cutoff point of a quantitative diagnostic test will inversely affect its sensitivity and specificity. Typically, raising the cutoff value will increase specificity (fewer false positives) and decrease sensitivity (more false negatives). Screening tests need high sensitivity; confirmatory tests need high specificity.

A Gynecologic Oncology Research Institute Isolates a Potential Tumor Marker