PTH and osteoporosis: Several studies have explored the relationship between bone turnover markers and osteoporosis, including parathyroid hormone (PTH), C-terminal telopeptide of type I collagen (β-CTX), N-terminal propeptide of type I procollagen (PINP), osteocalcin (OC), serum 25-hydroxyvitamin D3 (25-OH-D3), and alkaline phosphatase (ALP) (12).