This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Screening, Subject name: Social & Preventive Medicine
A study is planned to check stool occult blood positivity using hemoccult test among a group of paicipants aged 50 - 75 years. The test is repeated if result is positive. No repeating if the test is negative. What is the effect on sensitivity and specificity? 
Select and explain. 
A. Sensitivity increases specificity decreases, B. Sensitivity decreases specificity increases, C. Sensitivity unchanged specificity increases, D. Sensitivity increases specificity unchanged
B: Sensitivity decreases specificity increases
Answer: B: Sensitivity decreases specificity increases 
Explanation: SCREENING TESTS IN One test (after +ve result) after other Both tests applied together COMBINED SERIES PARALLEL SENSITIVITY Decreases Increases SPECIFICITY Increases Decreases PPV Increases Decreases NPV Decreases Increases