Submitted to: American Journal of Clinical Nutrition
Publication Type: Other
Publication Acceptance Date: December 1, 2003
Publication Date: May 1, 2004
Citation: Klevay, L.M. 2004. Chemical validation of X-ray absorptiometry [Letter to Editor]. American Journal of Clinical Nutrition. 79:887. Technical Abstract: Koo et al. (1) showed clearly that two, different dual-energy X-ray absorptiometers gave nearly identical results in both piglets and infants when estimates the bone mineral content, etc. were compared. Nearly all points fell on or near the lines in their graphs. They may have missed a golden opportunity to validate the use of radiology by the assessment of bone chemistry. Chemical analysis and radiodensity of bone have been compared only rarely (2). To illustrate, thirty-one vertebrae have been removed from 11 fresh cadavers, scanned by dual energy absorbtiometry, and converted to ash; radiologic measurements and ash were correlated (3). Both ash and calcium were correlated with radiologic measurements in six fetal, human femurs (4). Limited data from animals also revealed a correlation between radiologic measurements and bone ash (5-9). Ash is both non-specific and chemically complex. Calcium receives most radiological emphasis in this context because of its radiodensity; however, correlations from only six excised, fetal femurs do not inspire confidence. Bones are complex organs and it is important to provide evidence that radiodensity, which correlates well with fracture risk, correlates also with calcium, collagen or other proteins, phosphorus or even trace elements in bone. For the most part this evidence is lacking. Trace elements may be important because two supplementation trials (10,11) have shown benefits of copper in adult osteoporosis to complement numerous similar data on osteoporosis in children deficient in copper (for references see (2)). I hope that the authors (1) removed femurs, radii and vertebrae from the piglets for chemical analysis so that an important paper can be written to improve the validity of bone density measurements and to clarify mechanisms of bone pathology. Reference List 1. Koo WW, Hammami M, Hockman EM. Interchangeability of pencil-beam and fan-beam dual-energy X-ray absorptiometry measurements in piglets and infants. Am J Clin Nutr 2003;78:236-40. 2. Klevay LM, Wildman RE. Meat diets and fragile bones: inferences about osteoporosis. J Trace Elem Med Biol 2002;16:149-54. 3. Ho CP, Kim RW, Schaffler MB, Sartoris DJ. Accuracy of dual-energy radiographic absorptiometry of the lumbar spine: cadaver study. Radiology 1990;176:171-3. 4. Braillon PM, Salle BL, Brunet J, Glorieux FH, Delmas PD, Meunier PJ. Dual energy x-ray absorptiometry measurement of bone mineral content in newborns: validation of the technique. Pediatr Res 1992;32:77-80. 5. Kimmel DB, Wronski TJ. Nondestructive measurement of bone mineral in femurs from ovariectomized rats. Calcif Tissue Int 1990;46:101-10. 6. Griffin MG, Kimble R, Hopfer W, Pacifici R. Dual-energy x-ray absorptiometry of the rat: accuracy, precision, and measurement of bone loss. J Bone Miner Res 1993;8:795-800. 7. Hagiwara S, Lane N, Engelke K, Sebastian A, Kimmel DB, Genant HK. Precision and accuracy for rat whole body and femur bone mineral determination with dual X-ray absorptiometry. Bone Miner 1993;22:57-68. 8. Mitlak BH, Schoenfeld D, Neer RM. Accuracy, precision, and utility of spine and whole-skeleton mineral measurements by DXA in rats. J Bone Miner Res 1994;9:119-26. 9. Yamauchi H, Kushida K, Yamazaki K, Inoue T. Assessment of spine bone mineral density in ovariectomized rats using DXA. J Bone Miner Res 1995;10:1033-9. 10. Strause L, Saltman P, Smith KT, Bracker M, Andon MB. Spinal bone loss in postmenopausal women supplemented with calcium and trace minerals. J Nutr 1994;124:1060-4. 11. Eaton-Evans J, McIlrath EM, Jackson WE, McCartney H, Strain JJ. Copper supplementation and the maintenance of bone mineral density in middle-aged women. J Trace Elem Exp Med 1996;9:87-94.