Application to screening programs — MCQs

10 questions

A scientist in Chicago is studying a new blood test to detect Ab to EBV with increased sensitivity and specificity. So far, her best attempt at creating such an exam reached 82% sensitivity and 88% specificity. She is hoping to increase these numbers by at least 2 percent for each value. After several years of work, she believes that she has actually managed to reach a sensitivity and specificity much greater than what she had originally hoped for. She travels to China to begin testing her newest blood test. She finds 2,000 patients who are willing to participate in her study. Of the 2,000 patients, 1,200 of them are known to be infected with EBV. The scientist tests these 1,200 patients' blood and finds that only 120 of them tested negative with her new exam. Of the patients who are known to be EBV-free, only 20 of them tested positive. Given these results, which of the following correlates with the exam's specificity?

Group of 100 medical students took an end of the year exam. The mean score on the exam was 70%, with a standard deviation of 25%. The professor states that a student's score must be within the 95% confidence interval of the mean to pass the exam. Which of the following is the minimum score a student can have to pass the exam?

A 36-year-old female presents to clinic inquiring about the meaning of a previous negative test result from a new HIV screening test. The efficacy of this new screening test for HIV has been assessed by comparison against existing gold standard detection of HIV RNA via PCR. The study includes 1000 patients, with 850 HIV-negative patients (by PCR) receiving a negative test result, 30 HIV-negative patients receiving a positive test result, 100 HIV positive patients receiving a positive test result, and 20 HIV positive patients receiving a negative test result. Which of the following is most likely to increase the negative predictive value for this test?

An infectious disease investigator is evaluating the diagnostic accuracy of a new interferon-gamma-based assay for diagnosing tuberculosis in patients who have previously received a Bacillus Calmette-Guérin (BCG) vaccine. Consenting participants with a history of BCG vaccination received an interferon-gamma assay and were subsequently evaluated for tuberculosis by sputum culture. Results of the study are summarized in the table below. Tuberculosis, confirmed by culture No tuberculosis Total Positive interferon-gamma assay 90 6 96 Negative interferon-gamma assay 10 194 204 Total 100 200 300 Based on these results, what is the sensitivity of the interferon-gamma-based assay for the diagnosis of tuberculosis in this study?

A 6-month-old male presents for a routine visit to his pediatrician. Two months ago, the patient was seen for tachypnea and wheezing, and diagnosed with severe respiratory syncytial virus (RSV) bronchiolitis. After admission to the hospital and supportive care, the patient recovered and currently is not experiencing any trouble breathing. Regarding the possibility of future reactive airway disease, which of the following statements is most accurate?

Two studies are reviewed for submission to an oncology journal. In Study A, a novel MRI technology is evaluated as a screening tool for ovarian cancer. The authors find that the mean survival time is 4 years in the control group and 10 years in the MRI-screened group. In Study B, cognitive behavioral therapy (CBT) and a novel antidepressant are used to treat patients with comorbid pancreatic cancer and major depression. Patients receiving the new drug are told that they are expected to have quick resolution of their depression, while those who do not receive the drug are not told anything about their prognosis. Which of the following describes the likely type of bias in Study A and Study B?

During an evaluation of a new diagnostic imaging modality for detecting salivary gland tumors, 90 patients tested positive out of the 100 patients who tested positive with the gold standard test. A total of 80 individuals tested negative with the new test out of the 100 individuals who tested negative with the gold standard test. What is the positive likelihood ratio for this test?

A 65-year-old non-smoking woman with no symptoms comes to your clinic to establish care with a primary care provider. She hasn’t seen a doctor in 12 years and states that she feels very healthy. You realize that guidelines by the national cancer organization suggest that she is due for some cancer screening tests, including a mammogram for breast cancer, a colonoscopy for colon cancer, and a pap smear for cervical cancer. These three screening tests are most likely to be considered which of the following?

A 50-year-old male presents to his primary care physician for a routine check-up. He reports that he is doing well overall without any bothersome symptoms. His past medical history is significant only for hypertension, which has been well controlled with losartan. Vital signs are as follows: T 37.0 C, HR 80, BP 128/76, RR 14, SpO2 99%. Physical examination does not reveal any concerning abnormalities. The physician recommends a fecal occult blood test at this visit to screen for the presence of any blood in the patient's stool that might be suggestive of an underlying colorectal cancer. Which of the following best describes this method of disease prevention?

Q10

You are reviewing raw data from a research study performed at your medical center examining the effectiveness of a novel AIDS screening examination. The study enrolled 250 patients with confirmed AIDS, and 240 of these patients demonstrated a positive screening examination. The control arm of the study enrolled 250 patients who do not have AIDS, and only 5 of these patients tested positive on the novel screening examination. What is the NPV of this novel test?

Application to screening programs US Medical PG Practice Questions and MCQs

Question 1: A scientist in Chicago is studying a new blood test to detect Ab to EBV with increased sensitivity and specificity. So far, her best attempt at creating such an exam reached 82% sensitivity and 88% specificity. She is hoping to increase these numbers by at least 2 percent for each value. After several years of work, she believes that she has actually managed to reach a sensitivity and specificity much greater than what she had originally hoped for. She travels to China to begin testing her newest blood test. She finds 2,000 patients who are willing to participate in her study. Of the 2,000 patients, 1,200 of them are known to be infected with EBV. The scientist tests these 1,200 patients' blood and finds that only 120 of them tested negative with her new exam. Of the patients who are known to be EBV-free, only 20 of them tested positive. Given these results, which of the following correlates with the exam's specificity?

A. 82%
B. 90%
C. 84%
D. 86%
E. 98% (Correct Answer)

Explanation: ***98%*** - **Specificity** measures the proportion of **true negatives** among all actual negatives. - In this case, 800 patients are known to be EBV-free (actual negatives), and 20 of them tested positive (false positives). This means 800 - 20 = 780 tested negative (true negatives). Specificity = (780 / 800) * 100% = **98%**. *82%* - This value represents the *original sensitivity* before the scientist’s new attempts to improve the test. - It does not reflect the *newly calculated specificity* based on the provided data. *90%* - This value represents the *newly calculated sensitivity* of the test, not the specificity. - Out of 1200 EBV-infected patients, 120 tested negative (false negatives), meaning 1080 tested positive (true positives). Sensitivity = (1080 / 1200) * 100% = 90%. *84%* - This percentage is not directly derived from the information given for either sensitivity or specificity after the new test results. - It does not correspond to any of the calculated values for the new test's performance. *86%* - This percentage is not directly derived from the information given for either sensitivity or specificity after the new test results. - It does not correspond to any of the calculated values for the new test's performance.

Question 2: Group of 100 medical students took an end of the year exam. The mean score on the exam was 70%, with a standard deviation of 25%. The professor states that a student's score must be within the 95% confidence interval of the mean to pass the exam. Which of the following is the minimum score a student can have to pass the exam?

A. 45%
B. 63.75%
C. 67.5%
D. 20%
E. 65% (Correct Answer)

Explanation: ***65%*** - To find the **95% confidence interval (CI) of the mean**, we use the formula: Mean ± (Z-score × Standard Error). For a 95% CI, the Z-score is approximately **1.96**. - The **Standard Error (SE)** is calculated as SD/√n, where n is the sample size (100 students). So, SE = 25%/√100 = 25%/10 = **2.5%**. - The 95% CI is 70% ± (1.96 × 2.5%) = 70% ± 4.9%. The lower bound is 70% - 4.9% = **65.1%**, which rounds to **65%** as the minimum passing score. *45%* - This value is significantly lower than the calculated lower bound of the 95% confidence interval (approximately 65.1%). - It would represent a score far outside the defined passing range. *63.75%* - This value falls below the calculated lower bound of the 95% confidence interval (approximately 65.1%). - While close, this score would not meet the professor's criterion for passing. *67.5%* - This value is within the 95% confidence interval (65.1% to 74.9%) but is **not the minimum score**. - Lower scores within the interval would still qualify as passing. *20%* - This score is extremely low and falls significantly outside the 95% confidence interval for a mean of 70%. - It would indicate performance far below the defined passing threshold.

Question 3: A 36-year-old female presents to clinic inquiring about the meaning of a previous negative test result from a new HIV screening test. The efficacy of this new screening test for HIV has been assessed by comparison against existing gold standard detection of HIV RNA via PCR. The study includes 1000 patients, with 850 HIV-negative patients (by PCR) receiving a negative test result, 30 HIV-negative patients receiving a positive test result, 100 HIV positive patients receiving a positive test result, and 20 HIV positive patients receiving a negative test result. Which of the following is most likely to increase the negative predictive value for this test?

A. Decreased prevalence of HIV in the tested population (Correct Answer)
B. Increased prevalence of HIV in the tested population
C. Increased number of false positive test results
D. Increased number of false negative test results
E. Decreased number of false positive test results

Explanation: ***Decreased prevalence of HIV in the tested population*** - A **lower prevalence** of a disease in the population means there are fewer actual cases, making a **negative test result** more reliable in ruling out the disease. - This increases the probability that a person with a negative test truly does not have the disease, thus elevating the **negative predictive value (NPV)**. *Increased prevalence of HIV in the tested population* - A **higher prevalence** means there are more actual cases of HIV in the population. - In this scenario, a negative test result is less reassuring, as there's a greater chance of missing a true positive case, leading to a **decreased NPV**. *Increased number of false positive test results* - **False positives** are instances where a test indicates disease when it's not present; they do not directly impact the ability of a negative test to predict absence of disease. - While they affect the **positive predictive value (PPV)**, they do not directly alter the reliability of a negative result to exclude disease, so the NPV is not increased. *Increased number of false negative test results* - **False negatives** occur when a test indicates no disease, but the disease is actually present. - An increase in false negatives directly implies that a negative test result is less trustworthy, leading to a **decrease in the NPV**. *Decreased number of false positive test results* - A decrease in false positive results primarily improves the **positive predictive value (PPV)**. - While it indicates a more accurate test overall, it does not directly affect NPV, which measures the reliability of a negative test result in ruling out disease.

Question 4: An infectious disease investigator is evaluating the diagnostic accuracy of a new interferon-gamma-based assay for diagnosing tuberculosis in patients who have previously received a Bacillus Calmette-Guérin (BCG) vaccine. Consenting participants with a history of BCG vaccination received an interferon-gamma assay and were subsequently evaluated for tuberculosis by sputum culture. Results of the study are summarized in the table below. Tuberculosis, confirmed by culture No tuberculosis Total Positive interferon-gamma assay 90 6 96 Negative interferon-gamma assay 10 194 204 Total 100 200 300 Based on these results, what is the sensitivity of the interferon-gamma-based assay for the diagnosis of tuberculosis in this study?

A. 90/96
B. 100/300
C. 194/200
D. 90/100 (Correct Answer)
E. 194/204

Explanation: ***90/100*** - **Sensitivity** measures the proportion of **true positive** cases that are correctly identified by the test. - In this study, there are 90 true positive results (positive interferon-gamma assay in patients with confirmed tuberculosis) out of a total of 100 individuals with confirmed tuberculosis (90 + 10). *90/96* - This calculation represents the **positive predictive value** (90 true positives / 96 total positive tests). - It answers the question: "If the test is positive, what is the likelihood that the patient actually has the disease?" *100/300* - This value represents the prevalence of tuberculosis in the study population (100 confirmed cases / 300 total participants). - It does not reflect a measure of the test's diagnostic accuracy. *194/200* - This value represents the **specificity** of the test (194 true negatives / 200 total individuals without tuberculosis). - Specificity measures the proportion of true negative cases that are correctly identified by the test. *194/204* - This calculation represents the **negative predictive value** (194 true negatives / 204 total negative tests). - It answers the question: "If the test is negative, what is the likelihood that the patient does not have the disease?"

Question 5: A 6-month-old male presents for a routine visit to his pediatrician. Two months ago, the patient was seen for tachypnea and wheezing, and diagnosed with severe respiratory syncytial virus (RSV) bronchiolitis. After admission to the hospital and supportive care, the patient recovered and currently is not experiencing any trouble breathing. Regarding the possibility of future reactive airway disease, which of the following statements is most accurate?

A. “There is no clear relationship between RSV and the development of asthma.”
B. “Your child has a greater than 20% chance of developing asthma” (Correct Answer)
C. “Your child’s risk of asthma is less than the general population.”
D. “Your child has a less than 5% chance of developing asthma”
E. “Your child’s risk of asthma is the same as the general population.”

Explanation: ***“Your child has a greater than 20% chance of developing asthma”*** - Severe **RSV bronchiolitis** in infancy is a significant risk factor for the development of **recurrent wheezing** and **childhood asthma**. - Studies estimate that a substantial proportion, often greater than 20%, of infants with severe RSV bronchiolitis will go on to develop **asthma** later in childhood. *“There is no clear relationship between RSV and the development of asthma.”* - This statement is incorrect as there is a **well-established link** between severe RSV infection in early life and an increased risk of developing **asthma**. - Numerous epidemiological and longitudinal studies have documented this association. *“Your child’s risk of asthma is less than the general population.”* - This is incorrect, as severe RSV infection **increases** the risk of asthma, not decreases it. - Children with a history of severe RSV have a **higher incidence** of asthma compared to the general pediatric population. *“Your child has a less than 5% chance of developing asthma”* - This percentage is **too low** given the known association between severe RSV bronchiolitis and subsequent asthma. - The actual risk is considerably higher, typically falling into the range of 20-50% for those with severe RSV. *“Your child’s risk of asthma is the same as the general population.”* - This statement is inaccurate because severe RSV infection in infancy is a recognized independent **risk factor** for **asthma development**. - Therefore, the child's risk is elevated above that of the general population.

Question 6: Two studies are reviewed for submission to an oncology journal. In Study A, a novel MRI technology is evaluated as a screening tool for ovarian cancer. The authors find that the mean survival time is 4 years in the control group and 10 years in the MRI-screened group. In Study B, cognitive behavioral therapy (CBT) and a novel antidepressant are used to treat patients with comorbid pancreatic cancer and major depression. Patients receiving the new drug are told that they are expected to have quick resolution of their depression, while those who do not receive the drug are not told anything about their prognosis. Which of the following describes the likely type of bias in Study A and Study B?

A. Latency Bias; Golem effect
B. Confounding; Golem effect
C. Lead time bias; Golem effect
D. Lead time bias; Pygmalion effect (Correct Answer)
E. Latency bias; Pygmalion effect

Explanation: ***Lead time bias; Pygmalion effect*** - In Study A, the MRI technology detects ovarian cancer earlier, artificially making the survival time appear longer simply due to earlier diagnosis, not necessarily improved outcomes, which is characteristic of **lead time bias**. - In Study B, the patients receiving the new drug are told to expect quick resolution of their depression, leading to increased expectation of improvement, which describes the **Pygmalion effect** (a form of observer-expectancy effect where higher expectations lead to increased performance). *Latency Bias; Golem effect* - **Latency bias** refers to a delay in the manifestation of an outcome, which is not the primary issue in Study A's screening context. - The **Golem effect** is a form of negative self-fulfilling prophecy where lower expectations placed upon individuals by superiors/researchers lead to poorer performance, which is opposite to what is described in Study B. *Confounding; Golem effect* - **Confounding** occurs when an unmeasured third variable is associated with both the exposure and the outcome, distorting the observed relationship; while confounding is common, the scenario in Study A specifically points to a screening effect on survival time. - As mentioned, the **Golem effect** refers to negative expectations leading to poorer outcomes, which is not present in Study B. *Lead time bias; Golem effect* - **Lead time bias** correctly identifies the issue in Study A, as explaining the apparently longer survival as a result of earlier detection. - However, the **Golem effect** incorrectly describes the scenario in Study B, where positive expectations are given, not negative ones. *Latency bias; Pygmalion effect* - **Latency bias** is not the primary bias described in Study A; the immediate impact of early detection on survival statistics points to lead time bias. - The **Pygmalion effect** correctly describes the bias in Study B, where positive expectations from the researchers influence patient outcomes.

Question 7: During an evaluation of a new diagnostic imaging modality for detecting salivary gland tumors, 90 patients tested positive out of the 100 patients who tested positive with the gold standard test. A total of 80 individuals tested negative with the new test out of the 100 individuals who tested negative with the gold standard test. What is the positive likelihood ratio for this test?

A. 80/90
B. 90/100
C. 90/20 (Correct Answer)
D. 90/110
E. 10/80

Explanation: ***90/20*** - The **positive likelihood ratio (LR+)** is calculated as **sensitivity / (1 - specificity)**. To calculate this, we first need to determine the values for true positives (TP), false positives (FP), true negatives (TN), and false negatives (FN). - Given that 90 out of 100 actual positive patients tested positive, **TP = 90** and **FN = 100 - 90 = 10**. Also, 80 out of 100 actual negative patients tested negative, so **TN = 80** and **FP = 100 - 80 = 20**. - **Sensitivity** is the true positive rate (TP / (TP + FN)) = 90 / (90 + 10) = 90 / 100. - **Specificity** is the true negative rate (TN / (TN + FP)) = 80 / (80 + 20) = 80 / 100. - Therefore, LR+ = (90/100) / (1 - 80/100) = (90/100) / (20/100) = **90/20**. *80/90* - This option incorrectly represents the components for the likelihood ratio. It seems to misinterpret the **true negative** count and the **true positive** count. - It does not follow the formula for LR+ which is **sensitivity / (1 - specificity)**. *90/100* - This value represents the **sensitivity** of the test, which is the proportion of true positives among all actual positives. - It does not incorporate the **false positive rate** (1 - specificity) in the denominator required for the positive likelihood ratio. *90/110* - This option incorrectly combines different values, possibly by confusing the denominator for sensitivity or specificity calculations. - It does not correspond to the formula for the **positive likelihood ratio**. *10/80* - This value seems to relate to the inverse of the **false negative rate** (10/100) or misrepresents the relationship between false negatives and true negatives. - It is not correctly structured to represent the **positive likelihood ratio (LR+)**.

Question 8: A 65-year-old non-smoking woman with no symptoms comes to your clinic to establish care with a primary care provider. She hasn’t seen a doctor in 12 years and states that she feels very healthy. You realize that guidelines by the national cancer organization suggest that she is due for some cancer screening tests, including a mammogram for breast cancer, a colonoscopy for colon cancer, and a pap smear for cervical cancer. These three screening tests are most likely to be considered which of the following?

A. Tertiary prevention
B. Primary prevention
C. Secondary prevention (Correct Answer)
D. Cancer screening does not fit into these categories
E. Quaternary prevention

Explanation: ***Secondary prevention*** - **Secondary prevention** aims to detect and treat a disease early, before symptoms appear, to prevent its progression or recurrence. - **Cancer screening tests** such as mammograms, colonoscopies, and Pap smears fit this category perfectly as they are performed in asymptomatic individuals to identify early-stage cancer or pre-cancerous lesions. *Tertiary prevention* - **Tertiary prevention** focuses on minimizing the impact of an established disease and improving quality of life through treatment and rehabilitation. - This would involve managing existing cancer, not screening for it. *Primary prevention* - **Primary prevention** aims to prevent a disease from occurring in the first place, often through health promotion and risk reduction. - Examples include vaccination, lifestyle modifications (e.g., healthy diet, exercise), or avoiding smoking. *Cancer screening does not fit into these categories* - This statement is incorrect as cancer screening is a well-established component of preventive healthcare. - It clearly falls within the defined categories of prevention, specifically secondary prevention. *Quaternary prevention* - **Quaternary prevention** aims to protect patients from medical interventions that are likely to cause more harm than good, or to avoid over-medicalization. - This concept is distinct from screening for diseases and focuses on ethical considerations in medical care.

Question 9: A 50-year-old male presents to his primary care physician for a routine check-up. He reports that he is doing well overall without any bothersome symptoms. His past medical history is significant only for hypertension, which has been well controlled with losartan. Vital signs are as follows: T 37.0 C, HR 80, BP 128/76, RR 14, SpO2 99%. Physical examination does not reveal any concerning abnormalities. The physician recommends a fecal occult blood test at this visit to screen for the presence of any blood in the patient's stool that might be suggestive of an underlying colorectal cancer. Which of the following best describes this method of disease prevention?

A. Primary prevention
B. Primordial prevention
C. Secondary prevention (Correct Answer)
D. Tertiary prevention
E. Quaternary prevention

Explanation: ***Secondary prevention*** - **Secondary prevention** involves **early detection** of a disease or health problem in apparently healthy individuals. Screening tests, such as the fecal occult blood test used to detect colorectal cancer before symptoms arise, are prime examples of secondary prevention. - The goal is to identify and address the disease in its early stages, allowing for timely intervention and potentially improving outcomes. *Primary prevention* - **Primary prevention** aims to **prevent a disease from occurring** in the first place by reducing risk factors or increasing protective factors. Examples include vaccinations, promoting healthy diets, and regular exercise. - In this scenario, the individual is already being screened for a potential disease, not taking measures to prevent its initial development. *Primordial prevention* - **Primordial prevention** focuses on **preventing the development of risk factors** themselves at a societal level. This often involves public policy and environmental changes to promote healthier lifestyles. - It targets broad determinants of health before specific risk factors emerge in individuals, which is distinct from an individual screening test. *Tertiary prevention* - **Tertiary prevention** occurs **after a disease has been diagnosed** and aims to prevent progression, reduce complications, improve quality of life, and restore function. Examples include rehabilitation after a stroke or chemotherapy for cancer. - The patient in the scenario is asymptomatic and undergoing screening, not managing an existing, diagnosed condition. *Quaternary prevention* - **Quaternary prevention** aims to **protect patients from medical interventions** that are likely to cause more harm than good, or to mitigate the consequences of unnecessary or excessive medical care. It focuses on identifying and avoiding overmedicalization. - The fecal occult blood test is a standard screening tool in this context, not an intervention designed to counter the negative effects of over-treatment.

Question 10: You are reviewing raw data from a research study performed at your medical center examining the effectiveness of a novel AIDS screening examination. The study enrolled 250 patients with confirmed AIDS, and 240 of these patients demonstrated a positive screening examination. The control arm of the study enrolled 250 patients who do not have AIDS, and only 5 of these patients tested positive on the novel screening examination. What is the NPV of this novel test?

A. 240 / (240 + 15)
B. 240 / (240 + 5)
C. 240 / (240 + 10)
D. 245 / (245 + 10) (Correct Answer)
E. 245 / (245 + 5)

Explanation: ***245 / (245 + 10)*** - The **negative predictive value (NPV)** is calculated as **true negatives (TN)** divided by the sum of **true negatives (TN)** and **false negatives (FN)**. - In this study, there are 250 patients with AIDS; 240 tested positive (true positives, TP), meaning 10 tested negative (false negatives, FN = 250 - 240). There are 250 patients without AIDS; 5 tested positive (false positives, FP), meaning 245 tested negative (true negatives, TN = 250 - 5). Therefore, NPV = 245 / (245 + 10). *240 / (240 + 15)* - This calculation incorrectly uses the number of **true positives** (240) in the numerator and denominator, which is relevant for **positive predictive value (PPV)**, not NPV. - The denominator `(240 + 15)` does not correspond to a valid sum for calculating NPV from the given data. *240 / (240 + 5)* - This calculation incorrectly uses **true positives** (240) in the numerator, which is not part of the NPV formula. - The denominator `(240 + 5)` mixes true positives and false positives, which is incorrect for NPV. *240 / (240 + 10)* - This incorrectly places **true positives** (240) in the numerator instead of **true negatives**. - The denominator `(240+10)` represents **true positives + false negatives**, which is related to sensitivity, not NPV. *245 / (245 + 5)* - This calculation correctly identifies **true negatives** (245) in the numerator but incorrectly uses **false positives** (5) in the denominator instead of **false negatives**. - The denominator for NPV should be **true negatives + false negatives**, which is 245 + 10.

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