Multi-test algorithms — MCQs

10 questions

A 32-year-old man comes to the physician for a follow-up examination 1 week after being admitted to the hospital for oral candidiasis and esophagitis. His CD4+ T lymphocyte count is 180 cells/μL. An HIV antibody test is positive. Genotypic resistance assay shows the virus to be susceptible to all antiretroviral therapy regimens and therapy with dolutegravir, tenofovir, and emtricitabine is initiated. Which of the following sets of laboratory findings would be most likely on follow-up evaluation 3 months later? $$$ CD4 +/CD8 ratio %%% HIV RNA %%% HIV antibody test $$$

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 scientist in Boston is studying a new blood test to detect Ab to the parainfluenza virus 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 even greater than what she had originally hoped for. She travels to South America 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 the parainfluenza virus. The scientist tests these 1,200 patients’ blood and finds that only 120 of them tested negative with her new test. Of the following options, which describes the sensitivity of the test?

A 64-year-old man presents to the office for an annual physical examination. He has no complaints at this visit. His chart states that he has a history of hypertension, chronic obstructive pulmonary disease (emphysema), Raynaud’s disease, and glaucoma. He is a 30 pack-year smoker. His medications included lisinopril, tiotropium, albuterol, nifedipine, and latanoprost. The blood pressure is 139/96 mm Hg, the pulse is 86/min, the respiration rate is 16/min, and the temperature is 37.2°C (99.1°F). On physical examination, his pupils are equal, round, and reactive to light. The cardiac auscultation reveals an S4 gallop without murmur, and the lungs are clear to auscultation bilaterally. However, the inspection of the chest wall shows an enlarged anterior to posterior diameter. Which of the following is the most appropriate screening test for this patient?

A 32-year-old woman presented for her annual physical examination. She mentioned that her family history had changed since her last visit: her mother was recently diagnosed with breast cancer and her sister tested positive for the BRCA2 mutation. The patient, therefore, requested testing as well. If the patient tests positive for the BRCA1 or BRCA2 mutation, which of the following is the best screening approach?

A medical research study is beginning to evaluate the positive predictive value of a novel blood test for non-Hodgkin’s lymphoma. The diagnostic arm contains 700 patients with NHL, of which 400 tested positive for the novel blood test. In the control arm, 700 age-matched control patients are enrolled and 0 are found positive for the novel test. What is the PPV of this test?

A pharmaceutical corporation is developing a research study to evaluate a novel blood test to screen for breast cancer. They enrolled 800 patients in the study, half of which have breast cancer. The remaining enrolled patients are age-matched controls who do not have the disease. Of those in the diseased arm, 330 are found positive for the test. Of the patients in the control arm, only 30 are found positive. What is this test’s sensitivity?

A 28-year-old G1P0 woman at 16 weeks estimated gestational age presents for prenatal care. Routine prenatal screening tests are performed and reveal a positive HIV antibody test. The patient is extremely concerned about the possible transmission of HIV to her baby and wants to have the baby tested as soon as possible after delivery. Which of the following would be the most appropriate diagnostic test to address this patient’s concern?

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?

Q10

A patient presents to the emergency room in an obtunded state. The patient is a known nurse within the hospital system and has no history of any medical problems. A finger stick blood glucose is drawn showing a blood glucose of 25 mg/dL. The patient's daughter immediately arrives at the hospital stating that her mother has been depressed recently and that she found empty syringes in the bathroom at the mother's home. Which of the following is the test that will likely reveal the diagnosis?

Multi-test algorithms US Medical PG Practice Questions and MCQs

Question 1: A 32-year-old man comes to the physician for a follow-up examination 1 week after being admitted to the hospital for oral candidiasis and esophagitis. His CD4+ T lymphocyte count is 180 cells/μL. An HIV antibody test is positive. Genotypic resistance assay shows the virus to be susceptible to all antiretroviral therapy regimens and therapy with dolutegravir, tenofovir, and emtricitabine is initiated. Which of the following sets of laboratory findings would be most likely on follow-up evaluation 3 months later? $$$ CD4 +/CD8 ratio %%% HIV RNA %%% HIV antibody test $$$

A. ↓ ↓ negative
B. ↑ ↑ negative
C. ↓ ↑ negative
D. ↑ ↓ positive (Correct Answer)
E. ↓ ↑ positive

Explanation: ***↑ ↓ positive*** - With effective **antiretroviral therapy (ART)**, the **CD4+/CD8 ratio** would increase as **CD4+ T cell counts rise** and **CD8+ T cell counts decrease**. - **HIV RNA (viral load)** would significantly decrease (ideally to undetectable levels) due to the suppression of viral replication, but HIV antibodies would remain positive indefinitely. *↓ ↓ negative* - A decrease in the **CD4+/CD8 ratio** and **HIV RNA** (viral load) along with a negative **HIV antibody test** is inconsistent with successful ART. - A negative HIV antibody test would mean the patient was never infected, which contradicts the initial positive result and symptoms. *↑ ↑ negative* - An increase in the **CD4+/CD8 ratio** is expected with ART, but an increase in **HIV RNA** (viral load) indicates treatment failure. - A negative **HIV antibody test** is impossible after a confirmed positive result, regardless of treatment success. *↓ ↑ negative* - A decrease in the **CD4+/CD8 ratio** would suggest worsening immune function, while an increase in **HIV RNA** indicates treatment failure. - A negative **HIV antibody test** is not possible once a patient has developed antibodies to HIV. *↓ ↑ positive* - A decrease in the **CD4+/CD8 ratio** would indicate immune decline, contrary to the expected improvement with effective ART. - An increase in **HIV RNA (viral load)** would signify treatment failure, even if HIV antibodies remain positive.

Question 2: 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 3: A scientist in Boston is studying a new blood test to detect Ab to the parainfluenza virus 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 even greater than what she had originally hoped for. She travels to South America 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 the parainfluenza virus. The scientist tests these 1,200 patients’ blood and finds that only 120 of them tested negative with her new test. Of the following options, which describes the sensitivity of the test?

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

Explanation: ***90%*** - **Sensitivity** is calculated as the number of **true positives** divided by the total number of individuals with the disease (true positives + false negatives). - In this scenario, there were 1200 infected patients (total diseased), and 120 of them tested negative (false negatives). Therefore, 1200 - 120 = 1080 patients tested positive (true positives). The sensitivity is 1080 / 1200 = 0.90, or **90%**. *82%* - This value was the **original sensitivity** of the test before the scientist improved it. - The question states that the scientist believes she has achieved a sensitivity "even greater than what she had originally hoped for." *86%* - This value is not directly derivable from the given data for the new test's sensitivity. - It might represent an intermediate calculation or an incorrect interpretation of the provided numbers. *98%* - This would imply only 24 false negatives out of 1200 true disease cases, which is not the case (120 false negatives). - A sensitivity of 98% would be significantly higher than the calculated 90% and the initial stated values. *84%* - This value is not derived from the presented data regarding the new test's performance. - It could be mistaken for an attempt to add 2% to the original 82% sensitivity, but the actual data from the new test should be used.

Question 4: A 64-year-old man presents to the office for an annual physical examination. He has no complaints at this visit. His chart states that he has a history of hypertension, chronic obstructive pulmonary disease (emphysema), Raynaud’s disease, and glaucoma. He is a 30 pack-year smoker. His medications included lisinopril, tiotropium, albuterol, nifedipine, and latanoprost. The blood pressure is 139/96 mm Hg, the pulse is 86/min, the respiration rate is 16/min, and the temperature is 37.2°C (99.1°F). On physical examination, his pupils are equal, round, and reactive to light. The cardiac auscultation reveals an S4 gallop without murmur, and the lungs are clear to auscultation bilaterally. However, the inspection of the chest wall shows an enlarged anterior to posterior diameter. Which of the following is the most appropriate screening test for this patient?

A. Low-dose CT (Correct Answer)
B. Bronchoalveolar lavage with cytology
C. Magnetic resonance imaging
D. Pulmonary function tests
E. Chest radiograph

Explanation: ***Low-dose CT*** - This patient, a 64-year-old with a 30 pack-year smoking history and current emphysema (COPD), falls precisely within the **high-risk criteria** for lung cancer screening. - The **USPSTF guidelines** recommend annual **low-dose computed tomography (LDCT)** for individuals aged 50-80 years with a 20 pack-year smoking history who currently smoke or have quit within the past 15 years. *Bronchoalveolar lavage with cytology* - This is an **invasive diagnostic procedure** used to collect cells and fluid directly from the airways, typically performed when there is already suspicion of a lung malignancy or infection. - It is not a recommended **screening test** for asymptomatic individuals due to its invasiveness and the absence of clear evidence of benefit as a primary screening tool. *Magnetic resonance imaging* - **MRI** is primarily used for evaluating soft tissue structures, defining tumor extent, and assessing metastatic disease, but it is **not the preferred imaging modality for lung cancer screening** due to its lower spatial resolution for pulmonary nodules compared to CT and higher cost. - It involves longer scan times and is not routinely used for primary lung screening. *Pulmonary function tests* - **PFTs** are used to assess lung function, diagnose and monitor respiratory conditions like COPD, and evaluate the severity of airflow obstruction. - While important for managing his **emphysema**, PFTs do not directly screen for **lung cancer**; they measure how well the lungs work. *Chest radiograph* - A **chest X-ray** is less sensitive than LDCT for detecting small lung nodules and early-stage lung cancer due to its two-dimensional nature and potential for superimposition of structures. - While readily available and less expensive, it is **not recommended for lung cancer screening** as it has not shown a mortality benefit in randomized controlled trials compared to no screening.

Question 5: A 32-year-old woman presented for her annual physical examination. She mentioned that her family history had changed since her last visit: her mother was recently diagnosed with breast cancer and her sister tested positive for the BRCA2 mutation. The patient, therefore, requested testing as well. If the patient tests positive for the BRCA1 or BRCA2 mutation, which of the following is the best screening approach?

A. Order magnetic resonance imaging of the breast
B. Annual ultrasound, annual mammography, and monthly self-breast exams
C. Twice-yearly clinical breast exams, annual mammography, annual breast MRI, and breast self-exams (Correct Answer)
D. Annual clinical breast exams, annual mammography, and monthly self-breast exams
E. Refer to radiation therapy

Explanation: ***Twice-yearly clinical breast exams, annual mammography, annual breast MRI, and breast self-exams*** - For patients with **BRCA1 or BRCA2 mutations**, an intensive breast cancer screening protocol is recommended due to their highly increased lifetime risk of breast cancer. - This typically includes **semiannual clinical breast exams**, **annual mammography**, and **annual breast MRI**, often starting at a young age. *Order magnetic resonance imaging of the breast* - While MRI is a crucial part of screening for high-risk individuals, it is **not sufficient as a standalone screening modality**. - A comprehensive approach combining multiple screening methods is needed to maximize detection rates. *Annual ultrasound, annual mammography, and monthly self-breast exams* - **Breast ultrasound** is generally used as an adjunct to mammography when specific abnormalities are found or in women with dense breasts, not as a routine primary screening tool for BRCA carriers. - While **mammography** and **self-breast exams** are included, this option lacks the crucial **annual MRI** and **twice-yearly clinical breast exams** recommended for BRCA carriers. *Annual clinical breast exams, annual mammography, and monthly self-breast exams* - This protocol is **less intensive** than what is recommended for women with BRCA mutations. - It omits the essential **annual breast MRI** and the **twice-yearly clinical breast exams** that are critical for early detection in this high-risk population. *Refer to radiation therapy* - **Radiation therapy** is a treatment modality for existing cancer, not a screening approach for cancer prevention or early detection. - Referring for radiation therapy would be appropriate only after a diagnosis of breast cancer, not as a primary screening strategy.

Question 6: A medical research study is beginning to evaluate the positive predictive value of a novel blood test for non-Hodgkin’s lymphoma. The diagnostic arm contains 700 patients with NHL, of which 400 tested positive for the novel blood test. In the control arm, 700 age-matched control patients are enrolled and 0 are found positive for the novel test. What is the PPV of this test?

A. 400 / (400 + 0) (Correct Answer)
B. 700 / (700 + 300)
C. 400 / (400 + 300)
D. 700 / (700 + 0)
E. 700 / (400 + 400)

Explanation: ***400 / (400 + 0) = 1.0 or 100%*** - The **positive predictive value (PPV)** is calculated as **True Positives / (True Positives + False Positives)**. - In this scenario, **True Positives (TP)** are the 400 patients with NHL who tested positive, and **False Positives (FP)** are 0, as no control patients tested positive. - This gives a PPV of 400/400 = **1.0 or 100%**, indicating that all patients who tested positive actually had the disease. *700 / (700 + 300)* - This calculation does not align with the formula for PPV based on the given data. - The denominator `(700+300)` suggests an incorrect combination of various patient groups. *400 / (400 + 300)* - The denominator `(400+300)` incorrectly includes 300, which is the number of **False Negatives** (patients with NHL who tested negative), not False Positives. - PPV focuses on the proportion of true positives among all positive tests, not all diseased individuals. *700 / (700 + 0)* - This calculation incorrectly uses the total number of patients with NHL (700) as the numerator, rather than the number of positive test results in that group. - The numerator should be the **True Positives** (400), not the total number of diseased individuals. *700 / (400 + 400)* - This calculation uses incorrect values for both the numerator and denominator, not corresponding to the PPV formula. - The numerator 700 represents the total number of patients with the disease, not those who tested positive, and the denominator incorrectly sums up values that don't represent the proper PPV calculation.

Question 7: A pharmaceutical corporation is developing a research study to evaluate a novel blood test to screen for breast cancer. They enrolled 800 patients in the study, half of which have breast cancer. The remaining enrolled patients are age-matched controls who do not have the disease. Of those in the diseased arm, 330 are found positive for the test. Of the patients in the control arm, only 30 are found positive. What is this test’s sensitivity?

A. 330 / (330 + 30)
B. 330 / (330 + 70) (Correct Answer)
C. 370 / (30 + 370)
D. 370 / (70 + 370)
E. 330 / (400 + 400)

Explanation: ***330 / (330 + 70)*** - **Sensitivity** measures the proportion of actual **positives** that are correctly identified as such. - In this study, there are **400 diseased patients** (half of 800). Of these, 330 tested positive (true positives), meaning 70 tested negative (false negatives). So sensitivity is **330 / (330 + 70)**. *330 / (330 + 30)* - This calculation represents the **positive predictive value**, which is the probability that subjects with a positive screening test truly have the disease. It uses **true positives / (true positives + false positives)**. - It does not correctly calculate **sensitivity**, which requires knowing the total number of diseased individuals. *370 / (30 + 370)* - This expression is attempting to calculate **specificity**, which is the proportion of actual negatives that are correctly identified. It would be **true negatives / (true negatives + false positives)**. - However, the numbers used are incorrect for specificity in this context given the data provided. *370 / (70 + 370)* - This formula is an incorrect combination of values and does not represent any standard epidemiological measure like **sensitivity** or **specificity**. - It is attempting to combine false negatives (70) and true negatives (370 from control arm) in a non-standard way. *330 / (400 + 400)* - This calculation attempts to divide true positives by the total study population (800 patients). - This metric represents the **prevalence of true positives within the entire study cohort**, not the test's **sensitivity**.

Question 8: A 28-year-old G1P0 woman at 16 weeks estimated gestational age presents for prenatal care. Routine prenatal screening tests are performed and reveal a positive HIV antibody test. The patient is extremely concerned about the possible transmission of HIV to her baby and wants to have the baby tested as soon as possible after delivery. Which of the following would be the most appropriate diagnostic test to address this patient’s concern?

A. CD4+ T cell count
B. Viral culture
C. Polymerase chain reaction (PCR) for HIV RNA (Correct Answer)
D. Antigen assay for p24
E. EIA for HIV antibody

Explanation: ***Polymerase chain reaction (PCR) for HIV RNA*** - **PCR for HIV RNA** directly detects the viral genetic material, providing a definitive diagnosis of HIV infection in an infant. - Unlike antibody tests, PCR can distinguish between passively acquired maternal antibodies and actual infant infection, making it suitable for newborns. *CD4+ T cell count* - **CD4+ T cell count** is used to monitor the progression of HIV infection and immunosuppression, not for initial diagnosis, especially in neonates. - While it's an important marker for HIV disease, it does not confirm the presence of the virus itself in a newborn. *Viral culture* - **Viral culture** is a highly specific method for detecting HIV, but it is expensive, time-consuming, and technically demanding. - It is not routinely used for rapid early diagnosis in neonates due to its practical limitations and the availability of faster, reliable alternatives like PCR. *Antigen assay for p24* - The **p24 antigen test** can detect early HIV infection in adults, but its sensitivity is lower in neonates compared to PCR, especially immediately after birth. - It may not reliably detect infection in newborns due to low viral loads or the presence of maternal antibodies that complex the antigen. *EIA for HIV antibody* - An **EIA for HIV antibody** will detect maternal antibodies that have crossed the placenta, meaning it will be positive in nearly all infants born to HIV-positive mothers, regardless of the infant's infection status. - This test cannot distinguish between passive maternal antibody transfer and true infant infection.

Question 9: 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 10: A patient presents to the emergency room in an obtunded state. The patient is a known nurse within the hospital system and has no history of any medical problems. A finger stick blood glucose is drawn showing a blood glucose of 25 mg/dL. The patient's daughter immediately arrives at the hospital stating that her mother has been depressed recently and that she found empty syringes in the bathroom at the mother's home. Which of the following is the test that will likely reveal the diagnosis?

A. Fasting blood glucose
B. Urine metanephrines
C. Genetic testing
D. 24 hr cortisol
E. C-peptide level (Correct Answer)

Explanation: ***C-peptide level*** - A **low C-peptide level** in the presence of **hypoglycemia** and high insulin levels confirms the diagnosis of **exogenous insulin administration** (factitious hypoglycemia). - **C-peptide** is cleaved from **proinsulin** in equimolar amounts with endogenous insulin, making it an excellent marker to differentiate endogenous insulin production from exogenous insulin injection. - In this case: **Low C-peptide + High insulin + Hypoglycemia** = exogenous insulin administration. *Fasting blood glucose* - The patient already has documented **hypoglycemia (25 mg/dL)**, so an additional fasting blood glucose test would not provide further diagnostic information about the **cause** of hypoglycemia. - A single fasting blood glucose level indicates current glucose status but **does not differentiate** between endogenous insulin overproduction (insulinoma) and exogenous insulin administration. *Urine metanephrines* - **Urine metanephrines** are used to diagnose **pheochromocytoma**, a catecholamine-secreting tumor of the adrenal medulla. - Pheochromocytoma presents with **hypertension**, palpitations, headaches, and diaphoresis—**not hypoglycemia**. - This test is not relevant to the differential diagnosis of hypoglycemia. *Genetic testing* - **Genetic testing** might be considered for rare hereditary causes of hypoglycemia, such as congenital hyperinsulinism or genetic insulinoma syndromes (e.g., MEN1). - Given the clinical context (depressed nurse with access to insulin and empty syringes found at home), **exogenous insulin administration** is far more likely than a genetic condition. - Genetic testing is not the appropriate initial diagnostic step in this scenario. *24 hr cortisol* - A **24-hour urinary cortisol** test is used to diagnose **Cushing's syndrome** (cortisol excess), not hypoglycemia. - While **adrenal insufficiency** (cortisol deficiency) can cause hypoglycemia, it typically presents with **hypotension**, **hyponatremia**, **hyperkalemia**, and **hyperpigmentation**—features not described in this case. - The clinical presentation strongly suggests insulin-related hypoglycemia rather than adrenal insufficiency.

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