Biochemical abnormalities related to CKD–MBD and bone mineral density in patients with chronic kidney disease stages 3–5: A cross-sectional study

ABSTRACT Background: Chronic kidney disease (CKD) is associated with disturbances in mineral metabolism and skeletal health that contribute to CKD–mineral and bone disorder (CKD–MBD). Assessment of biochemical abnormalities and bone mineral density (BMD) may help characterize these changes in patients with advanced CKD. Objectives: This study aimed to assess the frequency of study-defined biochemical abnormalities related to CKD–MBD, evaluate BMD, and examine the relationship between mineral metabolism parameters and BMD among patients with CKD stages 3–5. Materials and Methods: A hospital-based cross-sectional observational study was conducted among 128 adults with CKD stages 3–5 at a tertiary-care center. Clinical and demographic details were recorded. Serum calcium, phosphorus, alkaline phosphatase, 25-hydroxyvitamin D (25(OH)D), and intact parathyroid hormone (iPTH) were assessed. BMD was measured at the lumbar spine and femoral neck using dual-energy X-ray absorptiometry. The primary outcome was the proportion of participants with one or more study-defined biochemical abnormalities related to CKD–MBD. This operational definition was study-specific and was not intended to represent a formal Kidney Disease: Improving Global Outcomes diagnosis of CKD–MBD. Results: Overall, 113/128 participants (88.3%) met the study-defined biochemical criteria. Hyperphosphatemia was present in 87 (68.0%), hypocalcemia in 62 (48.4%), elevated alkaline phosphatase in 60 (46.9%), 25(OH)D <30 ng/mL in 110 (85.9%), and elevated iPTH (>65 pg/mL) in 111 (86.7%). Among the participants meeting the study-defined outcome criteria, 98 (86.7%) had three or more biochemical abnormalities. Serum phosphorus increased from 4.11 ± 0.79 mg/dL in CKD stage 3 to 5.66 ± 0.81 mg/dL in stage 5, while iPTH increased from 126.58 ± 64.34 to 745.14 ± 264.36 pg/mL and 25(OH)D decreased from 22.20 ± 7.55 to 10.19 ± 6.68 ng/mL (all P < 0.001). Lumbar spine BMD and T -scores differed across the CKD stages ( P = 0.001 and 0.004, respectively), whereas femoral-neck BMD and T -scores did not. In unadjusted analysis, iPTH showed a weak negative correlation with lumbar spine BMD ( r = −0.168, P = 0.057) and lumbar spine T -score ( r = −0.206, P = 0.020). In multivariable analysis, iPTH was not independently associated with lumbar spine BMD ( β = 0.000006 g/cm 2 per pg/mL, 95% confidence interval: −0.000052 to 0.000065, P = 0.832). Conclusion: A high proportion of adults with CKD stages 3–5 had one or more study-defined biochemical abnormalities related to CKD–MBD, particularly in advanced CKD. Differences in mineral metabolism and lumbar spine BMD were observed across the CKD stages. These findings support the importance of biochemical assessment of mineral metabolism in patients with advanced CKD, while prospective multicenter studies are required to clarify their longitudinal relationship with skeletal and clinical outcomes.