Background: Bone turnover markers are used in the management of metabolic bone diseases. The commonly available bone resorption markers are C- and N-terminal telopeptide of type 1 collagen (CTX and NTX respectively) in monitoring patients with osteoporosis.
Aim: To assess the clinical utility of plasma CTX (ng/L) versus urine NTX (nmol BCE/mmol creatinine).
Methods: Fasting Metabolic Bone Study is a set of biochemistry tests (based on venous blood and urine samples after an overnight fast) requested for investigation and management of patients with metabolic bone diseases. From May to July 2022, PathWest laboratory dual reported CTX and NTX in all FMBS (NTX was the bone resorption marker since October 2004). Clinical details were identified from pathology request forms and available electronic medical records. To date, 232 out of 453 studies have been reviewed.
Results: We excluded patients with renal impairment (n=20) and age <30 (n=21). Given the sex specific reference intervals, our initial analysis was based on 151 female patients (NTX <50 nmol BCE/mmol creatine and CTX <800 ug/L). In our laboratory, bone resorption is well suppressed when NTX <20 nmol BCE/mmol creatinine and CTX <280 ng/L.
There was no correlation between NTX and CTX. The correlation coefficient was 0.45 when NTX 20-50 nmol BCE/mmol creatinine was compared to CTX, and 0.52 when CTX 280-800 mg/L was compared to NTX. There were 33 patients with suppressed NTX <20 but 7/33 (21%) had CTX >280 ug/L. Of the 19 patients on denosumab, 10 patients had suppressed NTX with corresponding CTX <90 ng/L. Further analysis will be performed in patients on bisphosphonate and menopausal hormone therapy.
Conclusion: Preliminary data identifies no clear correlation between NTX and CTX. If bone turnover markers are used in clinical management of patients, it is important to monitor with one specific marker.