Elevated parathyroid hormone levels in older women treated for osteoporosis using denosumab

Primary care physicians (PCPs) often struggle with elevated serum intact parathyroid hormone (iPTH) in osteoporotic patients on antiresorptive treatment, specifically, denosumab. As iPTH and calcium levels need to be within normal ranges to receive the next dose of denosumab, continuously high serum iPTH may necessitate additional tests to rule out pathological causes. We aimed to determine factors associated with iPTH elevation in a cohort of postmenopausal women receiving osteoporosis treatment.

A cross-sectional analysis of electronic medical records of patients 50 years and older who visited a geriatric osteoporosis clinic between October 1, 2014 and December 31, 2019, was conducted. We divided patients into 3 categories: not currently on treatment, on bisphosphonates or on denosumab. Percentage change in iPTH levels from baseline to 1 year follow-up was the outcome measure. Other variables used are age, body mass index, chronic co-morbidities, 25OH-vitamin D, calcium, TSH, glomerular filtration rate and femoral neck BMD. Linear regression models were used to assess independent associations between treatment group and iPTH changes.

Mean (SD) age of 173 participants in our study was 78 (± 10) years, and 71% were Caucasian. At follow-up, mean percent change of iPTH was 13.47 ± 62.76, 30.35 ± 61.17, and 39.60 ± 35.51 in the "no treatment", "bisphosphonate" and "denosumab" groups, respectively. Age was a predictor of elevated percent change of iPTH in the denosumab group.

Increasing age is associated with iPTH elevations in osteoporotic patients on denosumab. In the absence of any pathology, continuation of denosumab may be safe in lowering fracture risk. However, a larger study may be required to confirm this.