Toenail and Serum Measures as Biomarkers of Iron Levels

Abstract

BackgroundSerum iron is often assessed in epidemiologic studies, both as an exposure associated with diseases such as cancer and as an outcome indicating iron deficiency or overload. Toenails offer a convenient alternative to serum because of ease of collection, transport, and storage. Very few contemporary studies have examined the correlation between serum and toenail measures for trace metals.AimOur aim was to compare iron measures using serum and toenails on both a cross-sectional and longitudinal basis.MethodsUsing a subset of the US-wide prospective Sister Study cohort, we compared iron levels in toenails with three common serum biomarkers: iron, ferritin and percent transferrin saturation.ResultsAmong 146 participants who donated both blood and toenails at baseline, a subsample (59%) again provided specimens of both about 8 years later. Cross-sectional analyses included Spearman’s rank correlations between toenail and serum levels. We also considered maintenance of rank across time separately for toenails and for the serum measures. Overall, toenail values were not correlated with serum iron measures. Spearman correlations at baseline (follow-up) were 0.08 (0.09) for serum iron, 0.08 (0.07) for transferrin saturation, and -0.09 (-0.17) for ferritin. The Spearman correlation for toenail iron between the two time points was higher (0.47, 95% CI: 0.30, 0.64) than for serum iron (0.30, 95% CI: 0.09, 0.51) and transferrin saturation (0.34, 95% CI: 0.15, 0.54), but lower than that for ferritin (0.58, 95% CI: 0.43, 0.73).ConclusionBased on cross-sectional and repeated assessments, our evidence does not support an association between serum and toenail iron measures. Toenail iron measures did appear to be moderately repeatable but cannot be taken as a proxy for serum iron values and those exposure biomarkers may represent different compartments of iron storage.

Keywords: toenails, nails, iron, serum, comparisons