#6424 DIAGNOSTIC ACCURACY OF BONE TURNOVER MARKERS IN PATIENTS WITH VARIOUS DEGREES OF KIDNEY DYSFUNCTION AND PRIMARY OSTEOPOROSIS

Abstract

Abstract Background and Aims There are limited data available on the validity of bone turnover markers (BTMs) to predict bone turnover in patients with kidney dysfunction and primary osteoporosis. Method This is a cross-sectional retrospective study of patients with primary osteoporosis and eGFR<90 ml/min/1.73 m2 who had bone biopsy for clinical purposes for a time period of 8 years. CKD-EPI equation 2021 was used to calculate eGFR based on the mean serum creatinine readings. Bone biopsy samples were evaluated qualitatively using KDIGO TMV classification. Routine laboratory data were collected in addition to alkaline phosphatase, iPTH, cyclase activating (CAP) PTH, osteocalcin, bone specific alkaline phosphatase (BSAP), and N-telopeptide collagen (NTX). Results Study included 156 patients with mean age of 64.7 years. The majority of patients were females (93.6%). The mean BMI was 26.2 kg/m2. The mean eGFR was 70 ml/min with 78% of patients had eGFR from 60-90 ml/min/1.73 m2. CKD stage III was found in 19%, and 3% of patients had CKD stage IV. HTN was found in 47%, history of kidney stones in 9%, and fragility fractures in 77%. Bisphosphonates were the most used pre-biopsy bone specific medication (66%). Teriparatide was used in 10.9% and SERM was used in 7.7% of patients, while 31.4% of patients did not receive any bone anti-resorptive or anabolic medication “treatment naiive”. Bone cortical thickness and cancellous volume were low in 94.2%, while high bone turnover (HBT) was found in 42.9% and low bone turnover (LBT) in 57.1%. Mineralization was defective only in 9.6%, while osteoid thickness was increased in 5.8%. Figure 1 shows the distribution of bone turnover among study group. Baseline characteristics and routine laboratory data were not different between HBT and LBT. PTH, especially PTH CAP, and alkaline phosphatase tended to be higher in HBT but did not reach statistical significance. While BTMs (osteocalcin, BSAP and NTX) were significantly higher in HBT (Table 1). Using ROC curve analysis, the area under the curve (AUC) for BSAP, NTX and osteocalcin were 0.605, 0.660, 0.642, respectively. Combining the NTX with either BSAP or osteocalcin did not result in increasing the AUC. This was also the same when the three of them were combined. BTMs were able to discriminate bone turnover status only among patients with eGFR≥60 ml/min/1.73 m2 (Table 2). Conclusion Low bone turnover was found in 43% in treatment naïve patients with primary osteoporosis, with a higher prevalence among patients with eGFR≥60. In the study group, PTH and total alkaline phosphatase were not able to discriminate LBT from HBT, while BTMs showed a modest ability to discriminate the turnover status only among patients with eGFR≥60.