Cross-linked N-telopeptide of type I collagen

Cross-linked N-telopeptides of type I collagen (NTX or NTx) are a specific breakdown product of the type-I collagen found in bone cartilage, used as a marker of bone turnover. NTx is measured in the urine or serum.

Urine NTX levels of greater than 40 nmol/L indicate excessive bone turnover and is a sign of osteoporosis. Levels less than 14 may indicate over-aggressive treatment of osteoporosis with drugs such as bisphosphonates and can lead to "frozen bone syndrome".