Sensitivity Should Be High in a TB Screening Test for High TB Areas

In a high TB burden area where a new screening test is developed to capture missed cases, sensitivity (option b) must be high. 1

Rationale for Prioritizing High Sensitivity

A screening test designed to "include missed cases" must maximize sensitivity to ensure that individuals with TB are not incorrectly classified as disease-free 1
In high TB prevalence populations, the primary concern is identifying all infected individuals to prevent disease progression, transmission, and mortality 1
High sensitivity ensures that false-negative results are minimized, which is critical when the goal is explicitly to reduce missed diagnoses 1

In high TB burden areas, the positive predictive value (PPV) of screening tests naturally increases due to elevated disease prevalence 1
The American Thoracic Society guidelines explicitly state that in populations with 25-50% TB infection rates (such as close contacts in endemic areas), even tests with modest specificity maintain high PPV 1
When prevalence is high, a positive test result is highly likely to represent true infection, making sensitivity the limiting factor for case detection 1

Screening tests serve a different purpose than confirmatory diagnostic tests 1
The European guidelines for TB screening in high-risk migrants emphasize that screening tools should prioritize sensitivity to capture asymptomatic and early cases that would otherwise be missed 1
Chest radiography is recommended for active TB screening in migrants from high-incidence countries specifically because it can detect asymptomatic patients that symptom-based screening (which has higher specificity but lower sensitivity) would miss 1

Specificity is more important in low-prevalence settings where false-positives would outnumber true-positives 1
In high TB areas, the consequences of false-positives (unnecessary treatment) are outweighed by the consequences of false-negatives (ongoing transmission, disease progression, death) 1

PPV is already inherently high in high-prevalence settings regardless of test characteristics 1
PPV is a function of both test performance and disease prevalence—it automatically improves when prevalence increases 1
The question asks what parameter should be high in the test itself, not what will be high as a consequence of the epidemiologic setting

NPV, while important, is secondary to sensitivity in screening contexts where the goal is to find all cases 1
A test with high sensitivity will naturally have high NPV, but optimizing for NPV alone does not address the primary objective of reducing missed cases 1

The ATS/CDC guidelines recommend lower cut-points (≥5mm for tuberculin skin testing) in high-risk populations specifically to increase sensitivity, accepting some reduction in specificity 1, 2
Modern molecular tests like Xpert MTB/RIF are recommended for their 85-89% sensitivity in detecting pulmonary TB, representing a 23% improvement over smear microscopy 1, 3
The CHEST guidelines note that despite higher costs, tests with superior sensitivity are justified in screening programs because earlier diagnosis through sensitive testing reduces overall TB burden 1

Do not confuse screening test requirements with confirmatory test requirements—confirmatory tests prioritize specificity to avoid false treatment, while screening tests in high-burden areas prioritize sensitivity to avoid missed cases 1