The Correct Answer is B
Statement B is NOT true: screening tests are actually MORE useful for common diseases, not rare ones. This is a fundamental principle of screening program design that directly impacts the effectiveness and cost-benefit ratio of population-based screening initiatives.
Why Screening Tests Are More Useful for Common Diseases
The evidence clearly demonstrates that disease prevalence is a critical factor in determining screening utility:
For rare diseases, even highly accurate screening tests generate excessive false-positive results that lead to unnecessary anxiety, additional testing, and potential complications from diagnostic procedures 1
The positive predictive value of any screening test depends heavily on disease prevalence - when screening for rare conditions, even tests with high sensitivity and specificity will produce more false-positives than true-positives 2
Guidelines explicitly state that screening is not recommended when cancer is "so rare that a million persons would have to be screened to find one case" because the drawbacks (false-positives with associated harms) would outweigh benefits 1
Why the Other Statements ARE True
A) Early Diagnosis is the Goal
Screening tests fundamentally aim at early detection before symptoms appear. Many cancers are "highly treatable and curable if found early" - for example, colorectal cancer has 90% five-year survival when found before spreading versus only 9% after metastasis 1
C & D) False Results Occur
Screening tests are "not 100% accurate" and produce both false-positive and false-negative results 1. This is an inherent limitation acknowledged across all screening guidelines 3, 4, 2.
E) Test Characteristics Matter
Effective screening requires tests that are "easy to perform, low-cost, and have high sensitivity and specificity" 1. The fasting plasma glucose is preferred for diabetes screening specifically because it is "faster and easier to perform, more convenient, acceptable to patients, and less expensive" than alternatives 3.
Clinical Implications
When evaluating screening programs, remember:
- Common diseases with significant morbidity/mortality are better screening targets (colorectal cancer, diabetes, cervical cancer)
- Rare diseases generally should not be screened in asymptomatic populations unless there are specific high-risk factors
- The balance of benefits versus harms must always favor benefits - this calculation depends critically on disease prevalence 1