Negative predictive value — MCQs

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 new assay for Lyme disease has been developed. While the assay has been tested extensively in Maine, a group of inventors are planning to test it in Southern California. In comparison to the assay's performance in Maine, testing the assay in Southern California would affect the performance of the assay in which of the following ways?

A 20-year-old man presents to the emergency department with complaints of severe malaise, fevers, and sore throat for the past 7 days. He also has had episodes of nausea and vomiting during this period. He does not smoke or drink alcohol. There is no family history of liver disease. His blood pressure is 130/80 mm Hg, temperature is 38.3℃ (100.9℉), pulse is 102/min, and respiratory rate is 20/min. On physical examination, he appears ill with bilateral cervical lymphadenopathy. His tonsils are erythematous and enlarged. There is no jaundice and he is mildly dehydrated. Abdominal examination demonstrates splenomegaly. The laboratory findings are shown below: Hemoglobin 15 g/dL Platelet count 95,000/mm³ Leukocytes 13,500/mm³ Neutrophils 50% Atypical lymphocytes 34% AST 232 U/L ALT 312 U/L ALP 120 U/L GGT 35 U/L Total bilirubin 1.2 mg/dL Direct bilirubin 0.2 mg/dL PT 12 seconds The serologic test for hepatitis A, B, and C, CMV, and leptospirosis are negative. Serology for both serum IgM and IgG antibodies for EBV capsid antigen are positive, but the heterophile antibody test is negative. What is the most likely reason for the negative heterophile test?

You are developing a new diagnostic test to identify patients with disease X. Of 100 patients tested with the gold standard test, 10% tested positive. Of those that tested positive, the experimental test was positive for 90% of those patients. The specificity of the experimental test is 20%. What is the positive predictive value of this new test?

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?

You are reading through a recent article that reports significant decreases in all-cause mortality for patients with malignant melanoma following treatment with a novel biological infusion. Which of the following choices refers to the probability that a study will find a statistically significant difference when one truly does exist?

Four days after undergoing an elective total hip replacement, a 65-year-old woman develops a DVT that embolizes to the lung. Along with tachypnea, tachycardia, and cough, the patient would most likely present with a PaO2 of what?

A pharmaceutical company develops a sequential testing protocol for a rare genetic disorder (prevalence 0.01%). Initial screening test has sensitivity 95% and specificity 90%. Positive results undergo confirmatory testing with sensitivity 99% and specificity 99.5%. The company claims this approach achieves PPV >80% for the final positive result. Evaluate this claim and the rationale for sequential testing in this context.

A hospital system is implementing a sepsis screening algorithm using clinical criteria with sensitivity of 92% and specificity of 75%. False positives result in unnecessary antibiotics, cultures, and ICU evaluations costing $3,000 per case. Missing true sepsis cases (false negatives) results in average increased mortality and morbidity costs of $50,000 per case. Hospital sepsis prevalence is 8%. Evaluate the optimal threshold adjustment strategy.

A 58-year-old man with chronic cough undergoes evaluation for tuberculosis. A tuberculin skin test (TST) is positive (15mm induration). TST has sensitivity of 80% and specificity of 95% in immunocompetent adults. However, he received BCG vaccination as a child in Asia. Local TB prevalence is 0.5%, but his occupational exposure increases his pre-test probability to 10%. Evaluate the most appropriate interpretation and management approach.