Q) A 53-year-old dialysis patient in my clinic says her nephrologist told her she did not need a DXA scan because it was not valid for kidney patients. Why not?
Osteoporosis is a condition of reduced bone mass, causing decreased bone strength and leading to increased risk for fractures. The World Health Organization definition of osteoporosis is based on bone mineral density (BMD). While there is some overlap between idiopathic osteoporosis and chronic kidney disease–mineral bone disorder (CKD-MBD), both conditions have different pathophysiologic backgrounds and require different treatments.1
There is not an accurate correlation between BMD as measured by DXA and the type of CKD-associated bone disease.2 Patients with CKD typically have lower bone density than the general population, making the interpretation of DXA (dual x-ray absorptiometry) scans more complicated. This is due to focal areas of osteosclerosis, the presence of extraskeletal calcifications, and the variable presence of osteomalacia.
The gold standard for assessment and diagnosis of bone disease in CKD patients is the iliac crest bone biopsy. However, it is not frequently performed due to the painful and invasive nature of the procedure and the limitations in access to centers where it is performed and to experienced pathologists.
KDIGO (Kidney Disease Improving Global Outcomes) guidelines3 recommend that in patients with CKD stages 3 to 5D (see chart for explanation), measurements of serum parathyroid hormone or bone-specific alkaline phosphatase be used to evaluate bone disease, because markedly high or low values predict underlying bone turnover.
Shelly Levinstein, MSN, CRNP
Nephrology Associates of York
York, PA
REFERENCES
1. Toussaint N, Elder G, Kerr P. Bisphosphonates in chronic kidney disease; balancing potential benefits and adverse effects on bone and soft tissue. Clin J Am Soc Nephrol. 2009;4:221-233.
2. Tanenbaum N, Quarles LD. Bone disorders in chronic kidney disease. In: Greenberg A, Cheung AK, eds. Primer on Kidney Diseases. 5th ed. Philadelphia, PA: Elsevier Saunders; 2009:487-498.
3. Moe S, Drueke T, Cunningham J, et al; Kidney Disease: Improving Global Outcomes (KDIGO). Definition, evaluation, and classification of renal osteodystrophy: a position statement from Kidney Disease: Improving Global Outcomes (KDIGO). Kidney Int. 2006;69:1945-1953.
4. Gilbert S, Weiner DE. National Kidney Foundation’s Primer on Kidney Diseases. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:330.