This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concept of health and disease, Subject name: Social & Preventive Medicine
Screening test for vitamin D deficiency is 
Select and explain. 
A. 7-dehydrocholestrol, B. 1,25 dihydroxy vitamin D, C. 25 hydroxy vitamin D, D. Serum calcium levels
C: 25 hydroxy vitamin D
Answer: C: 25 hydroxy vitamin D 
Explanation: Total serum 25-hydroxyvitamin D (the major form of vitamin D that circulates in the body) is used for screening.Recently USPSTF (US preventive services task force) concluded that the evidence on screening for vitamin D deficiency in asymptomatic adults to improve health outcomes is insufficient