Objective <p>To establish whether the material in costal cartilages isoattenuating to urate on dual-energy CT is, in fact, urate.</p> Materials and methods <p>Under the Human Tissue Act, costal cartilage specimens from 12 donated embalmed cadavers were examined with DECT before and after storage in air, ethanol, and saline. Cadaveric tophi were examined as positive controls. The storage fluid was analyzed for urate. Raman spectroscopy was performed. The results were compared using Student <i>t</i>-tests and ANOVA.</p> Results <p>For cadavers 1–6, initial DECT isoattenuating volumes were 0.3–1.91 cm³ (mean 1.1). Three-month delayed volumes for those stored in air were 0.24–1.6 cm³ (mean 0.95). For those stored in ethanol, all volumes were zero (<i>p</i> = 0.009). For cadavers 7–12, initial volumes were 0.43–1.45 cm³ (mean 1.0). Three-month delayed volumes stored in distilled water were 0.13–0.62 cm³ (mean 0.3). Thirteen-month delayed volumes were 0–0.39 cm³ (mean 0.14, <i>p</i> = 0.001). Urate in the storage fluid for the costal cartilages was zero but that in the tophus storage fluid was high (1002 and 338 umol/L). The absent 632&#xa0;cm⁻¹ Raman spectra peak of costal cartilages 1 and 2 confirmed that no urate was present.</p> Conclusion <p>The isoattenuating material in costal cartilages on DECT is not urate, but other material that simulates the attenuation profile of urate under certain conditions. In clinical practice, isoattenuating material in costal cartilages on DECT can be regarded as artifactual.</p>