WBR0379
Jump to navigation
Jump to search
| Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biostatistics/Epidemiology |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[Prompt::A novel diagnostic serum assay is developed to detect enzyme XY in sera of patients with ulcerative colitis. Researchers enroll young adults with complaints of chronic diarrhea and abdominal pain and withdraw blood for the detection of serum enzyme XY among these patients. The second day, all patients undergo endoscopic examination, and biopsies are taken to confirm or rule out the diagnosis of ulcerative colitis. Results from patients' serum enzyme XY are then compared with results from the biopsy. Which equation is used to calculate the proportion of patients that are known to have ulcerative colitis on biopsy and also have detectable serum enzyme XY?]] |
| Answer A | AnswerA::1 - False Negative Rate |
| Answer A Explanation | [[AnswerAExp::Sensitivity is defined as the proportion of patients with ulcerative colitis (on biopsy) who test positive for ulcerative colitis using the serum enzyme XY test (true positive rate). Sensitivity is calculated by the following equation: [True Positive] / [True Positive + False Negative] or by the following equation: 1 - False Negative Rate. Both the sensitivity and the specificity are characteristics of the test and do not change with prevalence or pre-test probability.]] |
| Answer B | [[AnswerB::[True Negative] / [True Negative + False Positive]]] |
| Answer B Explanation | [[AnswerBExp::Specificity is defined as the proportion of patients without ulcerative colitis (on biopsy) who test negative for ulcerative colitis using the serum enzyme XY test (true negative rate). Specificity is calculated by the following equation: [True Negative] / [True Negative + False Positive] or by the following equation: Specificity = 1 - False Positive Rate. Both the sensitivity and the specificity are characteristics of the test and do not change with prevalence or pre-test probability.]] |
| Answer C | [[AnswerC::[True Positive] / [True Positive + False Positive]]] |
| Answer C Explanation | [[AnswerCExp::Positive predictive value (PPV) is defined as the proportion of positive test results that are truly positive. It is calculated by the following equation: PPV = [True Positive] / [True Positive + False Positive]. Unlike sensitivity and specificity, both the PPV and NPV vary with the prevalence of the disease and the pre-test probability.]] |
| Answer D | [[AnswerD::[True Negative] / [False Negative + True Negative]]] |
| Answer D Explanation | [[AnswerDExp::Negative predictive value (NPV) is defined as the proportion of negative test results that are truly negative. It is calculated by the following equation: NPV = [True Negative] / [False Negative + True Negative]. Unlike sensitivity and specificity, both the PPV and NPV vary with the prevalence of the disease and the pre-test probability.]] |
| Answer E | AnswerE::1 - False Positive Rate |
| Answer E Explanation | [[AnswerEExp::Specificity is defined as the proportion of patients without ulcerative colitis (on biopsy) who test negative for ulcerative colitis using the serum enzyme XY test (true negative rate). Specificity is calculated by the following equation: [True Negative] / [True Negative + False Positive] or by the following equation: Specificity = 1 - False Positive Rate.]] |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::Sensitivity is defined as the proportion of patients with ulcerative colitis (on biopsy) who test positive for ulcerative colitis using the serum enzyme XY test (true positive rate). Sensitivity is calculated by the following equation: [True Positive] / [True Positive + False Negative] or by the following equation: Sensitivity = 1 - False Negative Rate. Both the sensitivity and the specificity are characteristics of the test and do not change with prevalence or pre-test probability. Educational Objective: Sensitivity is the true positive rate and is calculated by the following equation: Sensitivity = 1 - False Negative Rate. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Ulcerative colitis, WBRKeyword::Sensitivity, WBRKeyword::Specificity, WBRKeyword::Positive predictive value, WBRKeyword::Negative predictive value, WBRKeyword::PPV, WBRKeyword::NPV, WBRKeyword::True positive rate, WBRKeyword::True negative rate, WBRKeyword::Enzyme XY |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |