Bone Abstracts

Background: Testing for 25(OH) vitamin D increased substantially as the number of potential clinical indications expanded beyond osteomalacia to include pre-denosumab testing. In Oxfordshire, testing for 25OHD is recommended prior to each administration of denosumab to reduce the risk of severe hypocalcaemia. We wanted to test whether the higher volume of vitamin D testing was due to increases in denosumab prescriptions.

Methods: The number of 25OHD tests performed in adults ≥50 years by Oxfordshire GP practices in 2024 and 2025 was obtained from the clinical biochemistry laboratory of the Oxford University Hospitals NHS Foundation Trust. The Open Prescribing database was used to source the number of denosumab prescriptions dispensed in GP practices, and the practice patient populations registered between Jan 1, 2024, and Dec 31, 2024, were obtained from NHS England. Non-parametric tests were used to compare rates.

Results: Between 2024 and 2025, the total number of vitamin D tests increased 15.6% from 22,252 to 25,730 (P 0.001), with no change in GP practice size (P 0.76). The changes in vitamin D and denosumab prescription rates among adults aged ≥50 years are shown in the table. While vitamin D testing and denosumab prescription rates were significantly correlated (P 0.001), wide variability persisted. If the top 10% of GP surgeries reduced their testing rate to the median, this would result in 259 fewer vitamin D tests in 2025, saving 7,931 in assay costs and reducing clinical and administrative workload in both primary and secondary care.

Conclusion: There is significant unwarranted variability in vitamin D testing rates among adults, leading to additional assays and increased clinical workload. Vitamin D testing for adults should be optimised by gaining a clearer understanding of the reasons for variation and implementing robust guidance as part of a quality improvement project.