Overestimation of Lumbar Spine Calcium with Dual Energy X-Ray Absorptiometry Scanning due to the Prescription of Lanthanum Carbonate in Patients with Chronic Kidney Disease

Abstract

Background/Aims: Dual energy X-ray absorptiometry (DEXA) scanning is used to assess bone mineral content and diagnose osteoporosis. We had noted anecdotal cases of patients attending for DEXA scanning following recent ingestion of barium-containing radiocontrast media, resulting in spuriously increased bone mineral content. Lanthanum carbonate is prescribed to chronic kidney disease patients as a non-calcium-containing phosphate binder, and as lanthanum is denser than barium, we wondered whether this could affect DEXA scan bone mineral estimations. Methods: DEXA scan records were reviewed from a cohort of 169 chronic dialysis patients, 24 (14%) of whom were prescribed lanthanum carbonate. Results: Estimation of segmental bone mineral content by DEXA was similar between the groups for the arms, legs, ribs, thoracic spine, hips and pelvis, apart from the lumbar spine for which it was greater for the lanthanum group (1.05 ± 0.05 vs. 0.98 ± 0.01 gm/cm², p < 0.05). Similarly, T and Z scores were higher in the lanthanum group for the lumbar spine (T score: –0.2 ± 0.4 vs. –0.92 ± 0.1; Z score: 0.68 ± 0.4 vs. –0.01 ± 0.1; p < 0.05), but not different for the hip (T score: –1.108 ± 0.28 vs. –0.966 ± 0.09; Z: score –0.49 ± 0.25 vs. –0.3 ± 0.01). Conclusion: DEXA scanning in patients prescribed lanthanum can lead to an erroneously high estimation of bone mineral content in areas of the skeleton adjacent to the bowel when the electron beam meets lanthanum.