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A Reproducibility Study for a Fluoride Assay in Bone

¹ Department of Oral Health Policy and Epidemiology, Harvard School of Dental Medicine, Harvard Medical School, Harvard University, Boston, Massachusetts; ² Department of Oral Biology, School of Dentistry, Medical College of Georgia, Augusta, Georgia; and ³ National Cancer Institute, Epidemiology and Biostatistics Program, Bethesda, Maryland

Requests for reprints: Thomas R. Fears, NIH/National Cancer Institute, Biostatistics Branch, EPN 403, 6130 Executive Boulevard, MSC 7368, Bethesda, MD 20892-7368. Phone: 301-496-8827; Fax: 301-402-0081. E-mail: fearst{at}exchange.nih.gov

Osteosarcoma is a rare malignancy of largely unknown etiology. Although there is no consistent evidence for an association between fluoridation and cancer, some concerns remain about osteosarcoma. As part of the design of a collaborative study, bone samples were collected to allow for an evaluation of the association between osteosarcoma risk and individual fluoride exposure measured by levels of fluoride in bone. In this report, we provide the results of pilot experiments to consider issues that arose during the study design and to assess the reliability of the bone assays. Correlations of fluoride levels between normal bone near the affected area and iliac crest bone were strong and positive. The day-to-day laboratory analysis of fluoride in human and deer jaw bone yielded acceptable average coefficients of variation below 10% and an overall estimate of 5%. The intraclass correlation (ICC) is of particular importance to epidemiologists because it indicates the effect of measurement error on study results. Here, the estimated ICC is 0.86, and the estimated downward bias is only 14%. Hence, the ICC is strong enough so that the estimates of the relative risk will suffer little attenuation from lab measurements. (Cancer Epidemiol Biomarkers Prev 2006;15(5):1035–7)