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: Orthopaedics
Osteoporosis is characterized by - 
Select and explain. 
A. Increased serum alkaline phosphatase, B. Decreased bone density, C. Wasting of muscles, D. Looser's zone seen
B: Decreased bone density
Answer: B: Decreased bone density 
Explanation: Osteoporosis is characterized by an abnormally low bone mass (low bone density) and defects in bone structure, a combination of which renders the bone unusually fragile and at greater than normal risk of fracture.