This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
ELISA is performed on a population with low prevalence. What would be the result of performing double screening ELISA tests? 
Select and explain. 
A. Increased sensitivity and positive predictive value, B. Increased sensitivity and negative predictive value, C. Increased specificity and positive predictive value, D. Increased specificity and negative predictive value
C: Increased specificity and positive predictive value
Answer: C: Increased specificity and positive predictive value 
Explanation: ELISA is an extremely good screening test with a high sensitivity of over 99.5% but low specificity. The specificity of the technique is increased by carrying out ELISA tests in a row using different HIV marker. Predictive value depends on sensitivity, specificity and the positive predictive value. Thus double ELISA increases the specificity and the positive predictive value. Ref:A.P.I Textbook of Medicine, 6th Edition, Page 135