SAT-522 Markers of Mineral Homeostasis and Bone Turnover in Patients Presenting with Acute Hip Fractures

Abstract

We previously reported on the very low rate of bone density assessment and vitamin D nutritional (VDN) status among 135 patients presenting with proximal hip fractures (ENDO-2018). It is generally assumed that bone turnover increases soon after a fracture, particularly after a major fracture such as hip. However, very little data exists on bone turnover markers (BTM) immediately after a hip fracture. In addition, it is unclear if the BTMs are related to prevailing VDN and parathyroid function. As part of ongoing project we assessed these characteristics in a larger sample (162), and further evaluated the indices of mineral homeostasis (as assessed by serum PTH and 25-OHD levels), and bone turnover (as assessed by serum CTX and bone specific alkaline phosphatase (BSAP); commonly used markers of bone resorption and formation respectively, in clinical practice. 162 patients were admitted with proximal femur fractures over 5y (1/1/2011 to 12/31/2016). The electronic health records (EHR) of 162 patients were reviewed to determine the rate of BMD testing, VDN, parathyroid function and BTMs. There were 112 women (69%) and 72 (44%) Caucasians with a mean age 78.6 ± 12.4y (range 49-98y). Mean 25-OHD was 22.6 ±12.9 ng/ml, and PTH was 61.1 ± 37.9 pg/ml. Mean serum CTX was 481 ± 241 mmol/mol and BSAP was 20.2 ± 14.6. Prevalence of vitamin D deficiency (<20ng/ml) was 44%, insufficiency (<30ng/ml) was 36%, and only 20% had optimal VDN. Serum PTH >70pg/ml in 25% (17/69), of whom 8 had 25-OD <20 ng/ml. By contrast, 42% (22/52) patients with serum PTH <70 pg/ml had a serum 25-OHD <20 ng/ml; the difference in vitamin D insufficiency was similar between the two groups of patients with and without hyperparathyroidism. Serum CTX was <300 mmol/mol in 25% (21/80) patients, which we considered as low bone turnover, and the mean BSAP in these patients was 13.4 ± 4.9 µg/L. Sixteen patients (20%) had serum BSAP >22 µg/L, all of whom had serum CTX >300 mmol/mol, which we considered as high bone turnover. The remaining 55% had high serum CTX 300-600 mmol/mol and the mean BSAP in these patients was 16.2 ± 7.9 µg/L. In a sub-set of 51 patients with BMD, osteopenia was seen in 13% using spine and 12% using femoral neck T-Scores, and osteoporosis in 9% using spine and 14% using femoral neck T scores. Neither spine nor femoral neck BMD correlated with VDN, PTH, or BTMs. Conclusions: Despite acute major fracture 26% have low bone turnover as assessed by BTMs. Only 25% had PTH >70 pg/ml that was not related to the prevailing VDN or renal function, but was related to age. High bone turnover was present in 74%, but was not related to PTH level or VDN. This is the first and most comprehensive study of mineral and skeletal homeostasis in a large sample of patients with hip fracture. Considering the large variation in BTMs, our findings may have therapeutic (antiresoprtive/anabolic) implications. Further studies are need to either confirm or refute our observations.