“Among nephrologists, we are less reluctant to perform DXA now,” Dr. Evenepoel said. “There will be many more DXA scans being performed. So there will be many more patients referred for advice on what to do with a low DXA BMD result.”
The lumbar spine and hip are the first areas where BMD should be measured, according to Dr. Evenepoel. But the distal forearm is also a good measurement site, because it’s almost purely cortical bone, and could help better define a patient’s fracture risk.
Get information on bone turnover when an elevated risk is identified. Clinicians need insight into whether a patient has high, normal or low bone turnover (i.e., the process of resorption followed by new bone replacement with little change in shape). Low turnover can lead to decreased bone toughness, and high turnover can lead to more porosity in the cortical part of the bone, as well as other abnormalities that can lower bone quality and boost the risk of fracture.
The usual markers of bone turnover are not very reliable in patients with CKD, and those that work best—such as bone alkaline phosphatase, a protein on bone-forming cells, and trimeric P1MP, a peptide originating from bone-forming cells—are not typically used in daily practice, according to Dr. Evenepoel. So clinicians will often need to look at total alkaline phosphatase, which typically correlates well with the bone-specific form and can offer insight into bone turnover. They should also refer patients for a bone biopsy when appropriate.
Tailor treatments according to bone turnover results. For patients with a high total alkaline phosphatase level, clinicians should look for an increasing trend, together with a high parathyroid hormone (PTH) level and high calcium. Those factors will point to high bone turnover. These patients should be treated to control the high turnover; suppress PTH with calcimimetics to better control phosphate levels.
For patients with low bone turnover, clinicians could use a non-calcium phosphate binder, lowering calcium and allowing PTH to increase and normalizing bone turnover, said Dr. Evenepoel.
Patients with frank osteoporosis—with very low BMD scores—should be advised to exercise, quit smoking, take vitamin D and get enough calcium. If there’s a suspicion of low bone turnover, clinicians should consider anti-osteoporosis therapy—an anabolic therapy—and an anti-resorptive agent if turnover seems to be normal.
Final Thoughts
Dr. Evenepoel drew attention to the counterintuitive nature of PTH in chronic kidney disease patients. Although PTH is almost universally elevated in these patients, its usual effect of high bone turnover isn’t seen in this population. Instead, Dr. Evenepoel said, the majority of CKD patients actually have low or normal bone turnover because of a hypo-responsiveness to PTH. This is due to downregulation of PTH receptors, the presence of dysfunctional PTH receptors and other phenomena.