Supplementary Material for: Association of Serum Bicarbonate with Bone Fractures in Hemodialysis Patients: The Mineral and Bone Disorder Outcomes Study for Japanese CKD Stage 5D Patients (MBD-5D)

Background/Aims: Bone fracture is often complicated in
hemodialysis (HD) patients. Metabolic acidosis is related to bone
disease and muscle wasting, but it is not known whether acid-base
disturbance is associated with the risk of bone fractures. The aim of
this study was to clarify the association of serum bicarbonate level
with bone fracture in HD patients. Methods: Using a
subcohort of the Mineral and Bone Disorder Outcomes Study for Japanese
CKD Stage 5D Patients (MBD-5D), 890 prevalent HD patients (age: 62 years
old, male: 62.8%, duration of dialysis: 8.3 years) with secondary
hyperparathyroidism were studied. After measuring predialysis serum
bicarbonate at a 2-day interdialytic interval, we prospectively followed
them every 3 months, and examined the occurrence of any type of bone
fracture or hospitalization due to fracture over a 3-year observation
period. Results: Seventy-four bone fractures and 47
hospitalizations due to fracture were observed during the follow-up
period. HD patients with serum bicarbonate <20 mmol/l had a 1.93 (95%
CI 1.01-3.71)-fold higher risk for all-cause fractures than those with
serum bicarbonate of 20.0-21.9 mmol/l. A higher bicarbonate level (≥22
mmol/l) was also related to an increased risk of bone fracture. A
restricted cubic regression spline disclosed that the higher or the
lower than 21.0 mmol/l of serum bicarbonate, the greater the risk for
bone fracture. Conclusion: Both a lower level and a higher
level of predialysis bicarbonate concentration were associated with
risk of bone fracture in HD patients with secondary hyperparathyroidism.