The use of a point of care device for monitoring the bone resorption biomarker urinary N-telopeptide in cancer patients with bone metastases.

Type I collagen is the major constituent of bone and its breakdown products are increasingly used as sensitive markers of bone resorption. The N-terminal peptide-bound crosslinks of type I collagen (NTX) can be measured in urine and is useful for the monitoring of patients with metastatic bone disease. Studies have shown that raised NTX levels in metastatic bone disease correlate with an increased risk of complications and pathological fracture. The development of accurate and instantaneous point of care devices (POCD) would facilitate patient treatment and avoid delays in awaiting results from specialist laboratories. This study assesses the clinical performance of a single use POCD (OSTEOMARK NTx Point of Care Rx Home Use) to monitor NTX levels in patients with metastatic bone disease. NTX was measured in duplicate in 136 urine samples from patients attending clinic with metastatic bone disease using the POCDs. In our centre the frequency of bisphosphonate treatment is dependent on the NTX level, which is categorised into three groups (0-50, 50-100 and >100 nmol BCE/mmol creatinine). We used these categories to compare the clinical performance of the POCDs to that of a laboratory immunoassay. From a total of 272 devices, 231 (84.9%) successfully recorded a value in nM BCE/mM creatinine. Statistical analysis of the measure of agreement between POCD and laboratory assay found moderate agreement between the two assays (kappa 0.508). Out of the 72 samples with a laboratory assay value of <50, 53 (73.6%) were found to be within the same group recorded by POCD. From the 20 samples with a laboratory assay value of >100, 19 (95.0%) were found to be within the same category using POCDs. The measurement of urinary NTX by POCD appears to be a viable option for the monitoring of metastatic cancer patients. Whilst POCDs appear to record higher values than laboratory assays, the correlation between devices is good and with further research the NTX categories could be modified to accommodate this variation.