The effects of formalin fixation and tissue embedding of bovine liver on copper, iron, and zinc analysis

Abstract

Veterinary analytical chemistry laboratories might be called upon to analyze formalin-fixed or paraffin-embedded tissue samples for trace minerals. The purpose of this study was to determine whether concentrations of copper (Cu), iron (Fe), and zinc (Zn) are comparable among fresh or frozen, formalin-fixed, and paraffin-embedded bovine liver samples on an as-received basis. Three liver sample subtypes (fresh or frozen, formalin-fixed, and paraffin-embedded) from 12 cows were collected and analyzed for Cu, Fe, and Zn concentrations. Concentrations were measured by using inductively coupled argon plasma atomic-emission spectroscopy. There was no significant difference in mineral measurements between fresh or frozen and formalin-fixed samples for Cu and Zn (both P ≥ 0.052). The median concentration of Fe was lower in the fresh or frozen samples than in the formalin-fixed samples. However, for every pair of fresh or frozen and paraffin-embedded samples for all 3 minerals, the fresh or frozen sample had a lower measurement than the paraffin-embedded sample (all P = 0.005). Differences in mineral measurements associated with tissue processing did not result in differences in classification (within or outside the reference range) for Fe. However, the classification of Cu and Zn was different up to 25% of the time with fresh or frozen versus formalin-fixed or embedded liver. Although Cu, Fe, and Zn concentrations attained from processed tissue may be useful, they must be evaluated with caution.