Pre-test probability assessment — MCQs

A scientist is studying the characteristics of a newly discovered infectious disease in order to determine its features. He calculates the number of patients that develop the disease over several months and finds that on average 75 new patients become infected per month. Furthermore, he knows that the disease lasts on average 2 years before patients are either cured or die from the disease. If the population being studied consists of 7500 individuals, which of the following is the prevalence of the disease?

A researcher is trying to determine whether a newly discovered substance X can be useful in promoting wound healing after surgery. She conducts this study by enrolling the next 100 patients that will be undergoing this surgery and separating them into 2 groups. She decides which patient will be in which group by using a random number generator. Subsequently, she prepares 1 set of syringes with the novel substance X and 1 set of syringes with a saline control. Both of these sets of syringes are unlabeled and the substances inside cannot be distinguished. She gives the surgeon performing the surgery 1 of the syringes and does not inform him nor the patient which syringe was used. After the study is complete, she analyzes all the data that was collected and performs statistical analysis. This study most likely provides which level of evidence for use of substance X?

A 67-year-old woman presents with right leg pain and swelling of 5 days’ duration. She has a history of hypertension for 15 years and had a recent hospitalization for pneumonia. She had been recuperating at home but on beginning to mobilize and walk, the right leg became painful and swollen. Her temperature is 37.1°C (98.7°F), the blood pressure is 130/80 mm Hg, and the pulse is 75/min. On physical examination, the right calf is 4 cm greater in circumference than the left when measured 10 cm below the tibial tuberosity. Dilated superficial veins are present on the right foot and the right leg is slightly redder than the left. There is some tenderness on palpation in the popliteal fossa behind the knee. Which of the following is the best initial step in the management of this patient’s condition?

A 43-year-old woman presents to her primary care physician with complaints of mild shortness of breath and right-sided chest pain for three days. She reports that lately she has had a nagging nonproductive cough and low-grade fevers. On examination, her vital signs are: temperature 99.1 deg F (37.3 deg C), blood pressure is 115/70 mmHg, pulse is 91/min, respirations are 17/min, and oxygen saturation 97% on room air. She is well-appearing, with normal work of breathing, and no leg swelling. She is otherwise healthy, with no prior medical or surgical history, currently taking no medications. The attending has a low suspicion for the most concerning diagnosis and would like to exclude it with a very sensitive though non-specific test. Which of the following should this physician order?

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 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 16-year-old presents to the primary care physician because he has noticed an increase in the size of his breast tissue over the past 3 years. He states that he is significantly taller than his entire class at school although he feels increasingly weak and uncoordinated. He performs at the bottom of his grade level academically. On physical exam the patient has marked gynecomastia with small firm testes. The physician decides to perform a karyotype on the patient. What is the most likely outcome of this test?

A 60-year-old-man presents to his physician with worsening myalgias and new symptoms of early fatigue, muscle weakness, and drooping eyelids. His wife presents with him and states that he never used to have such symptoms. His medical history is significant for gout, hypertension, hypercholesterolemia, diabetes mellitus type II, and pilocytic astrocytoma as a teenager. He denies smoking, drinks a 6-pack of beer per day, and endorses a past history of cocaine use but currently denies any illicit drug use. His vital signs include temperature 36.7°C (98.0°F), blood pressure 126/74 mm Hg, heart rate 87/min, and respiratory rate 15/min. Physical examination shows minimal bibasilar rales, but otherwise clear lungs on auscultation, grade 2/6 holosystolic murmur, 3/5 strength in all extremities, and benign abdominal findings. The Tensilon test result is positive. Which of the following options explains why a chest CT should be ordered for this patient?

A 71-year old man is brought to the emergency department because of progressively worsening shortness of breath and fatigue for 3 days. During the last month, he has also noticed dark colored urine. He had an upper respiratory infection 6 weeks ago. He underwent a cholecystectomy at the age of 30 years. He has hypertension, hyperlipidemia, and type 2 diabetes mellitus. He immigrated to the US from Italy 50 years ago. Current medications include simvastatin, lisinopril, and metformin. He appears pale. His temperature is 37.1°C (98.8°F), pulse is 96/min, respirations are 21/min, and blood pressure is 150/80 mm Hg. Auscultation of the heart shows a grade 4/6 systolic murmur over the right second intercostal space that radiates to the carotids. Laboratory studies show: Leukocyte count 9,000/mm3 Hemoglobin 8.3 g/dL Hematocrit 24% Platelet count 180,000/mm3 LDH 212 U/L Haptoglobin 15 mg/dL (N=41–165) Serum Na+ 138 mEq/L K+ 4.5 mEq/L CL- 102 mEq/L HCO3- 24 mEq/L Urea nitrogen 20 mg/dL Creatinine 1.2 mg/dL Total bilirubin 1.8 mg/dL Stool testing for occult blood is negative. Direct Coombs test is negative. Echocardiography shows an aortic jet velocity of 4.2 m/s and a mean pressure gradient of 46 mm Hg. Which of the following is the most appropriate next step in management to treat this patient's anemia?

A 5-year-old boy is brought to the physician because of behavioral problems. His mother says that he has frequent angry outbursts and gets into fights with his classmates. He constantly complains of feeling hungry, even after eating a full meal. He has no siblings, and both of his parents are healthy. He is at the 25th percentile for height and is above the 95th percentile for weight. Physical examination shows central obesity, undescended testes, almond-shaped eyes, and a thin upper lip. Which of the following genetic changes is most likely associated with this patient's condition?