PPV, NPV, Likelihood Ratios

A screening test for a rare disease has a likelihood ratio positive (LR+) of 8 and a likelihood ratio negative (LR−) of 0.1. Which statement best describes the clinical utility of this test?

A 38-year-old woman with no prior history of tuberculosis undergoes tuberculin skin test (TST) screening at her workplace. The TST is positive (induration ≥5 mm). The TST has a sensitivity of 85% and specificity of 90% in the general population. The prevalence of active TB in her region is 1%. Which investigation is the most appropriate next step to confirm active tuberculosis?

A 42-year-old woman from rural Maharashtra presents with a 3-month history of persistent cough and low-grade fever. Chest X-ray shows an upper lobe infiltrate. A tuberculin skin test (TST) is performed and reads 15 mm induration at 48 hours. In this population, the prevalence of active TB is 5%. The TST has a sensitivity of 85% and specificity of 90% for active TB. What is the positive predictive value (PPV) of this TST result, and what does it tell us about the likelihood of active TB in this patient?

A rapid diagnostic test for COVID-19 (RT-PCR) in symptomatic patients has sensitivity 95% and specificity 98%. In a high-prevalence setting (20% disease prevalence), which diagnostic parameter best distinguishes this test's ability to confirm infection when positive versus exclude infection when negative?

Regarding positive predictive value (PPV) and negative predictive value (NPV) in diagnostic test evaluation, all of the following statements are correct EXCEPT: