THE UTILITY OF BONE HEALTH INDEX SDS SCORES IN MEASURING BONE DENSITY IN CHILDREN WITH END STAGE KIDNEY DISEASE

Abstract Background and Aims Decreased bone mineral density (BMD) is well recognised in patients on dialysis. Lower DXA-BMD predicts incident fractures in patients with CKD 3a-5D. However while bone age (BA) Xrays are routinely performed to assess delays in bone age and density, DXA scans are not available widely. We compared the utility of bone density findings using automated measurements performed on routine BA Xrays and DXA scans. Method In our tertiary paediatric renal unit, patients on renal replacement therapy are reviewed within a joint dialysis/endocrine clinic by an nephrologist and endocrinologist,with annual radiological bone health assessment using hand and wrist Xray using Bone Xpert™ software. This automates assessment of BMD on hand Xrays, correcting for delays in bone age and calculates bone health index standard deviation score (BHI-SDS) using measurements of cortical thickness and mineralisation of metacarpal bones. In any patient with abnormal BMD on BA Xray or uncontrolled hyperparathyroidism, DXA was performed (measured as whole body (minus head) and in lumbar spine (L1–L4)). DXA-BMD Z scores were automatically calculated using normative data. A review of the results obtained was performed to compare these investigations of bone mineralisation status in our paediatric dialysis patients. Results 14 patients with ESRD on renal replacement therapy had both BHI-SDS and DXA BMD Z scores measured. Median chronological age was 12.6 years at DXA densitometry (range 5.1-16.3 years) with median BA of 11.5 years (range 4.4-14.8 years). All patients where BA Xray was performed had evidence of renal osteodystrophy radiographically. Median BHI-SDS was -1.2 (range -3.56 to 1.5). Median lumbar spine Z-score was -0.5 (range-3.6-2.9) and median WBMH Z-score was -1.2 (range -2.6-1.5). Pearson correlation coefficients with BHI-SDS were 0.77 and 0.8 respectively. Only 4/15 (27%) who had DXA performed had reported low BMD. Only one had objectively measured loss of vertebral height on vertebral fracture assessment. However there were two patients with undiagnosed scoliosis and one patient with an anterior wedge shaped fracture identified on DXA. These patients were referred for orthopaedic management. Conclusion The utility of BHI- SDS to measure bone density in paediatric patients with ESRD has not been reported. There appears to be good correlation between BHI SDS scores and DXA scan Z score measurements in paediatric patients with ESRD on renal replacement therapy. The advantages of using BHI SDS is that it is less expensive, more easily performed, more widely available and takes into account the delay in bone age often found in these children. BHI-SDS is a measure derived from assessment of the peripheral skeleton, in contrast to DXA, which measures bone health in the total skeleton or spine. BHI-SDS appears to be a useful initial measure to quantify bone density in patients with radiological changes consistent with renal osteodystrophy in the peripheral skeleton. However all children with low BHI-SDS should proceed to DXA scan as this may detect spinal abnormalities in addition.