Gene expression of the secreted glycoprotein Dkk-3 is upregulated during cellular senescence in prostate basal epithelial cells and altered in age-related disorders of the human prostate. In order to quantify the influence of such age- and disease-related changes of Dkk-3 levels in body fluids, we established a highly specific and sensitive indirect IEMA. Results revealed a significant increase of Dkk-3 blood plasma levels in the elderly (1.17+/-0.36 vs. 1.61+/-0.61 nmol/L) indicating a non-negligible physiological role and its use as a marker for senescence not only in vitro but also in vivo.