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Osteoporosis and chronic kidney disease are a growing concern in the elderly population. Over the past few decades, the ability to predict fracture risk has been significantly improved through diagnostic tools, such as the dual-energy X-ray absorptiometry (DXA) scan and the Fracture Risk Assessment Tool (FRAX). The aim of the study was to evaluate the prevalence of osteoporosis and its risk factors in a cohort of elderly CKD patients
Transversal study that included elderly patients (> 65 years old) with CKD G4-5 followed at the nephrology outpatient clinic of the Clinical Hospital of the Federal University of Paraná in Curitiba, Brazil. Glomerular filtration rate (GFR) was estimated by the CKD-EPI equation based on creatinine serum levels. Biochemical analysis of bone mineral metabolism measured were total alkaline phosphatase (AP), total calcium (Ca), phosphate (P), bicarbonate and intact parathormone (PTH). Bone mass and trabecular bone score (TBS) was evaluated by DXA. The diagnosis of osteoporosis was based on a T-score of ≤ −2.5 at the proximal radius 33%, lumbar spine or femur neck. The risk of bone fracture was further assessed by the FRAX calculation tool.
Forty-six patients (age 79.2 ± 7.9 years; male, 65.7%; 89.1% white race) were included. 22 of them (47,8%) had criteria for bisphosphonate treatment (osteoporosis or osteopenia with high-risk FRAX). 20 patients (43.4%) had diabetes mellitus. 52.3% of the patients were over 80 years old, 21 (45.7%) patients had frailty syndrome, 32.61% were on palliative care and had an average functionality of 70% (Palliative performance score). PTH was 171.8 ± 56.57 pg/mL; Ca was 9.35 ± 0.52 mg/dL; P was 3.66 ±0.67 mg/dL; AP was 81.57 ± 27.45 IU/L and Vitamin D was 28.42 ± 9.57 ng/mL. Nine (19.5%) patients reported a history of previous fracture. The mean eGFR was 23.4 ± 6.3 ml/min/1.73m2; most of the patients (85.4%) had CKD G4. Bone mineral density (BMD) at the femoral neck was on 0.682 ± 0.13 g/cm2. TBS was 1.25 ± 0.13. Although 52% of patients had osteoporosis, only 20.8% had high-risk FRAX. It was noticed a positive correlation between body mass index (BMI) and BMD at the femoral neck (r=0.39; P 0.007); whereas High-risk FRAX showed a significant association with previous fracture (p=0.0006). There was no difference among clinical, demographic, laboratory and densitometric characteristics between osteoporotic and non-osteoporotic patients.
Elderly patients with CKD present a high prevalence of osteoporosis, being the BMI the only risk factor associated with BMD. This finding highlights the importance of assessing BMD in CKD patients. Despite the high prevalence of osteoporosis, a well-known fracture risk assessment tool, FRAX might not be capable of identifying a high risk of fragility fracture in most of them. This discordance suggests this tool might underestimate the real risk of fracture in CKD elderly patients, suggesting that FRAX still requires improvement, considering the complexity of the interaction between CKD and the skeleton.