Using Kryofix as alternative for formalin results in more optimal and standardized immunostaining of paraffin sections.

Although used for over one century formalin has several disadvantages which Kryofix, an alternative fixative for paraffin blocks used in Leiden for 6 years, does not have. In this study the effects of Kryofix on tissue regarding immunohistochemistry are compared with those of buffered formalin. All markers studied showed enhanced staining in the Kryofix blocks after 4 hours of fixation, whilst in some cases the immunostaining of the formalin blocks was even negative. For all markers, the sera could be further diluted for the Kryofix sections, for some with as much as a factor 20, enhancing the cost-effectiveness of the method. We established that for formalin, the fixation time strongly influenced the results. For Kryofix there was no time factor: the immunostaining results of 1 hour fixation were identical to those after 3 months of fixation. This study shows that by this method of fixation, in which there is no cross-linking of proteins, immunostaining of paraffin sections is optimized and standardized.